JP2008233376A - Method for evaluating electrostatic latent image, device for evaluating electrostatic latent image, optical scanner, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device to achieve high-resolution measurement of charge distribution or potential distribution made on the surface of a photoreceptor in micron order, which is extremely difficult in the conventional technology. <P>SOLUTION: The device for evaluating an electrostatic latent image includes: an irradiation means 2 irradiating a photoreceptor sample 17 with a charged particle beam ; a detection means 5 detecting the signal of the charged particle obtained by such irradiation; an image processing means 51 functioning as a measuring means for measuring the state of the charge distribution of the photoreceptor sample 17; an exposure means 3 forming a plurality of latent image patterns on the photoreceptor sample 17; and an LD drive part 21 and a control means 20 functioning as a light emission control means for controlling light emission by the light source of the exposure means 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a method and apparatus for evaluating an electrostatic latent image formed on a photoreceptor, an optical scanning apparatus to which the evaluation method is applied, a copying machine having the optical scanning apparatus, a printer, a facsimile machine, a plotter, and the like. The present invention relates to an image forming apparatus such as a multifunction peripheral provided with at least one of them.
The present invention can be applied to a measuring device for electrostatic characteristics of a photoconductor, a measuring device for surface charge distribution, a measuring device for surface potential distribution, and a measuring device for reciprocity failure phenomenon.

As a method for observing an electrostatic latent image using an electron beam, there is Patent Document 1 or the like. Samples are limited to samples that can store and hold LSI chips and electrostatic latent images.
That is, a normal photoconductor that causes dark decay cannot be measured. Since a normal dielectric can hold a charge semipermanently, even if measurement is performed over time after forming a charge distribution, the measurement result is not affected. However, in the case of a photoreceptor, since the resistance value is not infinite, the charge cannot be held for a long time, dark decay occurs, and the surface potential decreases with time.
The time that the photoconductor can hold the charge is at most several tens of seconds even in the dark room. Therefore, even if an attempt is made to observe in a scanning electron microscope (SEM) after charging / exposure, the electrostatic latent image disappears in the preparation stage.

Therefore, the present applicant has proposed in Japanese Patent Application No. 2002-103355 and Japanese Patent Application No. 2003-43587 a method for measuring an electrostatic latent image even for a photoconductor sample having dark decay.
If there is a charge distribution on the sample surface, an electric field distribution corresponding to the surface charge distribution is formed in the space. For this reason, the secondary electrons generated by the incident electrons are pulled back by this electric field, and the amount reaching the detector is reduced. Therefore, a portion where the electric field intensity is strong is dark and a weak portion is bright and contrasted, and a contrast image corresponding to the surface charge distribution can be detected.
Therefore, when exposed, the exposed portion is black and the non-exposed portion is white, and the electrostatic latent image formed thereby can be measured.

JP 03-49143 A Japanese Patent Laid-Open No. 03-29867 Japanese Patent No. 3009179 JP-A-11-184188 Japanese Patent Laid-Open No. 2004-77714 JP 2003-295696 A JP 2003-305881 A JP 2005-166542 A Japanese Patent Laid-Open No. 2003-241403

By the way, even if the total exposure energy density given to the photoconductor is the same, the photoconductor has a reciprocity failure phenomenon in which the latent image formation state differs when the relationship between the light amount and the exposure time is different.
In general, when the exposure energy is constant, the sensitivity (latent image depth) decreases as the amount of light increases, causing a change in the toner adhesion amount, resulting in a difference in image density. It is considered that the cause is that the amount of recombination of carriers increases and the amount of carriers reaching the surface decreases when the amount of light is strong. In the case of a multi-beam scanning optical system, as shown in FIG.

In addition, it has been found that the reciprocity failure phenomenon also occurs depending on the peripheral image. That is, depending on whether the adjacent or adjacent area is an exposed part or a non-exposed part, the latent image state affects the toner adhesion amount.
The reciprocity failure phenomenon depends on the CGL film thickness, carrier mobility, quantum efficiency, and carrier generation amount among the characteristic values of the photoreceptor. For this reason, it is desirable to provide an imaging system that includes a photoconductor and a scanning optical system in which reciprocity failure is unlikely to occur. However, the conventional measurement method can only obtain a spatial resolution of only a few millimeters and analyze the mechanism. However, sufficient accuracy could not be obtained.

An object of the present invention is to provide a method and an apparatus capable of measuring a charge distribution or a potential distribution generated on the surface of a photoconductor, which has been extremely difficult in the prior art, in a micron order with high resolution. An object of the present invention is to provide an apparatus for evaluating an electrostatic latent image on a photoreceptor.
It is another object of the present invention to provide a high-quality optical scanning device and image forming apparatus.
It is well known that the surface charge described here is spatially dispersed in the sample. For this reason, the surface charge refers to a state in which the charge distribution state is largely distributed in the in-plane direction compared to the thickness direction. Further, the charge includes not only electrons but also ions.
Further, there may be a state in which there is a conductive portion on the surface and a voltage is applied to the conductive portion, thereby causing a potential distribution on the surface of the sample or in the vicinity thereof.

  In order to achieve the above object, the invention according to claim 1 is directed to irradiating a photoconductor sample having a surface charge distribution or a surface potential distribution with a charged particle beam, and using the detection signal obtained by the irradiation, In the method of measuring an electrostatic latent image of a body sample, a plurality of latent image patterns are formed on the photoconductor sample, the electrostatic latent image measured by the measurement method is captured as an image, and each latent image pattern is extracted. An electrostatic latent image evaluation method characterized by evaluating variations in the plurality of latent image patterns.

  According to the second aspect of the present invention, there is provided an irradiating unit for irradiating a photosensitive sample with a charged particle beam, a detecting unit for detecting a signal of a charged particle obtained by the irradiation, and a charge distribution state of the photosensitive sample Measuring means for measuring the electrostatic capacity, exposure means for forming a plurality of latent image patterns on the photoreceptor sample, and light emission control means for controlling light emission of the light source of the exposure means. It is a latent image evaluation apparatus.

According to a third aspect of the present invention, in the electrostatic latent image evaluation apparatus according to the second aspect, the extracting means for extracting the electrostatic latent images of the plurality of latent image patterns acquired by the measuring means for each latent image pattern; And calculating means for calculating the latent image area of each latent image pattern, and comparing means for comparing the latent image areas calculated by the calculating means.
According to a fourth aspect of the present invention, in the electrostatic latent image evaluation apparatus according to the third aspect, the exposure control means for forming a plurality of latent image patterns by fixing the image surface light quantity, lighting time, and beam diameter of the exposure means. And the calculating means calculates a variance of the latent image pattern area at that time.

According to a fifth aspect of the present invention, in the electrostatic latent image evaluation apparatus according to the second aspect, a latent image pattern is formed on the photoreceptor sample in a vacuum chamber, and the exposure unit is disposed outside the vacuum chamber. It is characterized by being.
According to a sixth aspect of the present invention, in the electrostatic latent image evaluation apparatus according to the second aspect, the exposure unit includes a scanning optical system that deflects and scans light beams from a plurality of light sources by the light deflection unit, and the light deflection unit. It has a synchronous detection means for detecting the scanning beam.

According to a seventh aspect of the present invention, in the electrostatic latent image evaluation apparatus according to the sixth aspect, scanning is performed on different light deflection surfaces of the light deflection means in order to form a plurality of latent image patterns.
According to an eighth aspect of the present invention, there is provided an optical scanning device that scans a photosensitive member with a plurality of light beams emitted from a light source via an optical scanning element including a light deflecting unit, and the photosensitive member according to a peripheral latent image pattern. It has an exposure control means for changing the exposure energy density applied to.

According to a ninth aspect of the present invention, in the optical scanning device according to the eighth aspect, the exposure control means is more advantageous in forming a latent image of an isolated dot in which the neighboring area is not exposed than in forming a latent image in which the neighboring area is exposed. The exposure condition is controlled so that the exposure energy density is set low.
According to a tenth aspect of the present invention, in the image forming apparatus, a latent image is formed by scanning the photosensitive member using the optical scanning device according to the eighth or ninth aspect, and is developed and visualized. And

According to the present invention, since the causal relationship between the design parameters and exposure conditions of the optical scanning device and the latent image forming conditions can be clarified, it is possible to provide a high-quality and highly stable optical scanning device.
By forming multiple latent image patterns and measuring the latent image pattern area ratio at that time, the degree of latent image pattern variation due to uneven charging, photoconductor sensitivity, electrostatic characteristics, electrostatic fatigue, etc. can be determined. It is possible to grasp the latent image forming ability from the photoconductor / exposure to latent image formation.
By feeding back to the design, the process quality of each process is improved, so that high image quality, high durability, high stability, and energy saving can be realized.
As a result, the cause of image density unevenness and countermeasures can be taken, and the output image quality can be improved.

According to the present invention, a plurality of latent image patterns are formed under the conditions of laser power, LD lighting time, and beam diameter fixed, and the latent image pattern area ratio at that time is calculated, whereby the light beam spot diameter and image plane are calculated. Even if the amount of light and the lighting time are constant, the influence of the latent image area, that is, the toner adhesion amount can be evaluated by the surrounding latent image pattern, and parameters necessary for the exposure conditions for making the toner adhesion amount constant are set appropriately. It becomes possible to do.
By arranging the exposure optical system outside the vacuum to form a plurality of latent image patterns, it becomes possible to suppress the influence of the vibration of the deflector such as the polygon motor and the electromagnetic field of the optical scanning device. As a result, the trajectory of the electron beam can be prevented from being affected, and the measurement accuracy is improved.

According to the present invention, it is possible to form a two-dimensional latent image pattern by using a scanning optical system with a plurality of light sources as exposure means. As a result, various two-dimensional latent image patterns can be formed, and correspondence with actual toner images is facilitated. As a result, the output image quality can be improved.
By scanning with different deflection surfaces to form a latent image pattern, it is possible to analyze the influence on the image density caused by the reciprocity failure phenomenon. As a result, charging / exposure and development time can be set appropriately. As a result, the cause of image density unevenness and countermeasures can be taken, and the output image quality can be improved.

According to the present invention, in an optical scanning device having a plurality of light beams, a uniform static image can be obtained regardless of the state of the peripheral latent image pattern by changing the exposure energy density applied to the photoconductor according to the peripheral image pattern. An electrostatic latent image can be formed.
In the latent image formation of isolated dots where adjacent dots are not exposed, the adjacent dots are exposed by controlling the exposure conditions so that the exposure energy density is set lower than the latent image formation where adjacent dots are exposed. It is possible to make the areas of the isolated latent image that is not exposed and the latent image on which the adjacent dots are exposed, so that it is possible to provide a high-quality optical scanning device.
By using an image forming apparatus characterized in that a latent image is formed using the optical scanning device described above, developed and visualized, an image forming system that is less likely to cause uneven image density is formed. An apparatus can be provided.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows the configuration of an electrostatic latent image evaluation apparatus according to an embodiment of the present invention. The electrostatic latent image evaluation apparatus 1 includes a charged particle irradiation unit 2 as an irradiation unit that irradiates a charged particle beam, an exposure unit 3 as an exposure unit, a sample placement unit 4, primary inversion charged particles, secondary electrons, and the like. It has the detector 5 etc. as a detection means to detect.
As used herein, charged particles refer to particles that are affected by an electric or magnetic field, such as an electron beam or an ion beam. Hereinafter, an embodiment in which an electron beam is irradiated will be described.

The electron beam irradiation unit 2 includes an electron gun 6 for generating an electron beam, a suppressor electrode 7 and an extraction electrode (extractor) 8 for controlling the electron beam, and an acceleration for controlling the energy of the electron beam. A voltage 9, a condenser lens 10 for focusing the electron beam generated from the electron gun 6, a beam blanker (beam blanking electrode) 11 for turning the electron beam on and off, a gate valve 12, an electron beam An aperture (movable stop) 13 for controlling the irradiation current, a stigmator (astigmatism correction) 14, a scanning lens (deflection electrode) 15 for scanning the electron beam that has passed through the beam blanker 11, and a scanning lens It comprises an objective lens (electrostatic objective lens) 16 for condensing 15 again. A driving power source (not shown) is connected to each lens.
In FIG. 1, reference numeral 17 denotes a photoreceptor sample (hereinafter also simply referred to as “sample”), 18 denotes voltage application means, 19 denotes an entrance window, 20 denotes control means (microcomputer), and 21 denotes an LD driving unit. , GND indicates the ground.
In the case of an ion beam, a liquid metal ion gun or the like is used instead of an electron gun.

Details of the exposure unit 3 can be described as an embodiment of an optical scanning device, which is shown in FIG.
The exposure unit 3 includes a light source (multiple light sources) 22 such as an LD (laser diode) having a sensitivity with respect to the photosensitive member, a collimating lens 23, an aperture 24, a condensing lens 25, and the like. It is possible to generate a beam profile.
Further, an appropriate exposure time and exposure energy can be irradiated by the control means 20 and the LD driving unit 21. The control means 20 and the LD driving unit 21 are both light emission control means and exposure control means.
In FIG. 2, reference numeral 26 denotes a folding mirror, 27 denotes a polygon mirror as light deflecting means, 28 denotes a first scanning lens, 29 denotes a second scanning lens (long lens), 30 denotes synchronization detecting means, Each is shown.

In order to form a line pattern, a scanning mechanism using a galvano mirror or a polygon mirror shown in FIG.
By adding a scanning mechanism, an arbitrary latent image pattern including a line pattern can be formed in the bus line direction of the photoreceptor.
Further, in order to form a latent image pattern at a predetermined position, as shown in FIG. 2A, there may be provided synchronization detection means for detecting a scanning beam from the light deflection means. The shape of the sample 17 may be a flat surface or a curved surface.
When the sample is a cylindrical photoconductor, the configuration shown in FIG. 3 can be adopted. In FIG. 3, reference numeral 31 denotes a reflection mirror, and 32 denotes a static elimination unit.
First, the photosensitive member sample 17 is irradiated with an electron beam. By setting the acceleration voltage | Vacc | to an acceleration voltage higher than the acceleration voltage at which the secondary electron emission ratio is 1, the amount of incident electrons exceeds the amount of emitted electrons, so that electrons are accumulated in the sample 17 and charge-up is performed. Wake up. As a result, the sample 17 can be negatively charged uniformly. By appropriately performing the acceleration voltage and the irradiation time, a desired charging potential can be formed.
Thereafter, the amount of incident electrons is lowered so that the electrostatic latent image can be observed.

Next, the photosensitive member sample 17 is exposed by the exposure unit 3. The optical system of the exposure unit 3 is adjusted so as to form a desired beam diameter and beam profile. The required exposure energy is a factor determined by the photoreceptor characteristics, but is usually about 2 to 6 mJ / m2. For photoreceptors with low sensitivity, ten or more mJ / m 2 may be required. The charging potential and the necessary exposure energy are preferably set in accordance with the photoreceptor characteristics and process conditions.
Thereby, an electrostatic latent image can be formed on the photoreceptor sample 17.
The photoconductor sample 17 is scanned with an electron beam, the secondary electrons emitted are detected by a scintillator (detector 5), converted into an electric signal, and a contrast image is observed.

In this way, a bright and dark contrast image is generated where the charged portion has a large amount of detected secondary electrons and the exposed portion has a small amount of detected secondary electrons. The dark part can be regarded as a latent image part by exposure. The light / dark boundary at the time of one exposure can be set as the latent image diameter D of the one-beam spot latent image. Further, the area of the dark part can be set to the latent image area S by the one-beam spot latent image.
Similarly, the area of the dark part when the exposure is performed a plurality of times at different locations can also be set as the latent image area.
If there is a charge distribution on the sample surface, an electric field distribution corresponding to the surface charge distribution is formed in the space. For this reason, the secondary electrons generated by the incident electrons are pushed back by this electric field, and the amount reaching the detector 5 decreases. Accordingly, at the charge leak portion, the exposed portion is black and the non-exposed portion is white, and a contrast image corresponding to the surface charge distribution can be measured.

FIG. 7A illustrates the potential distribution in the space between the charged particle trap 34 of the detector 5 and the sample 17 in an explanatory diagram with contour lines. Since the surface of the sample 17 is uniformly charged in a negative polarity except for the portion where the potential is attenuated due to light attenuation, and the charged particle trap 34 is given a positive potential, In the “potential contour line group”, the “potential becomes higher” as it approaches the charged particle trap 34 from the surface of the sample 17.
Accordingly, the secondary electrons el1 and el2 generated at the points Q1 and Q2 in the figure, which are “negatively uniformly charged portions” in the sample 17, are drawn to the positive potential of the charged particle trap 34, and the arrow G1. And is displaced as indicated by the arrow G2 and is captured by the charged particle trap 34.
On the other hand, in FIG. 7A, the point Q3 is “a portion where the negative potential is attenuated by light irradiation”, and the arrangement of the potential contour lines is “as shown by the broken line” in the vicinity of the point Q3. “The closer to Q3 point, the higher the potential”. In other words, an electric force constrained on the sample 17 side acts on the secondary electrons el3 generated in the vicinity of the point Q3, as indicated by an arrow G3. For this reason, the secondary electron el3 is captured in the “potential hole” indicated by the broken line potential contour and does not move toward the charged particle trap 24.

FIG. 7B schematically shows the “potential hole”.
That is, the intensity of secondary electrons (number of secondary electrons) detected by the charged particle trap 34 is such that the portion with the high intensity is “the portion of the ground of the electrostatic latent image (the portion that is uniformly negatively charged FIG. 7 ( The portion having a low intensity corresponds to “the image portion of the electrostatic latent image (the portion irradiated with light” and the portion represented by the point Q3 in FIG. 7A). ) ”.
Therefore, if the electrical signal obtained by the detector 5 which is a secondary electron detector is sampled at an appropriate sampling time by the signal processing means 50 shown in FIG. Potential distribution: V (X, Y) can be specified for each “micro-region corresponding to sampling”, and the above-mentioned surface potential distribution (potential contrast image): V (X, Y) by the image processing means 51 as the measuring means shown in FIG. By constructing Y) as two-dimensional image data and outputting it with an output device, an electrostatic latent image can be obtained as a visible image.
For example, if the intensity of secondary electrons to be captured is expressed as “brightness or weakness”, the image portion of the electrostatic latent image is dark, the ground portion is bright and contrasted, and a bright and dark image corresponding to the surface charge distribution is obtained. It can be expressed (output). Of course, if the surface potential distribution is known, the surface charge distribution can also be known.

FIG. 4 shows the relationship between the latent image pattern by one light beam and the LD light emission pattern.
The horizontal axis of the light source emission condition is the time axis, and the vertical axis indicates the timing at which the LD emits light. (A) is a latent image of a 1-dot isolated pattern. For LD control, after detecting a synchronization signal, a delay is applied until the light beam reaches the latent image area. Then, an appropriate exposure amount and duty (exposure time) are set, and an appropriate exposure energy density is applied to the photoconductor. Thereby, a latent image is formed. Similarly, (b) is 1by1 which repeats ON / OFF for each dot, and (c) is a latent image formation pattern and an LD light emission pattern for one dot line.
By scanning a light beam on the charged photoreceptor sample in this way, a plurality of latent image patterns distributed in the in-plane direction of the photoreceptor and shifted in time are formed, compared with a beam diameter of several tens of microns. The electrostatic latent image can be measured with a sufficiently small resolution, and the electrostatic latent image can be evaluated.

The scanning optical system of the exposure unit 3 is preferably arranged outside the vacuum chamber so that the influence of the vibration of the deflector such as a polygon motor or the influence of the electromagnetic field does not affect the trajectory of the electron beam. By moving away from the position of the electron beam orbit, the influence of disturbance can be suppressed. The scanning optical system is preferably made incident through an optically transparent entrance window 19.
FIG. 5 is a cross-sectional view of a modified example of the electrostatic latent image evaluation apparatus. As shown in FIG. 5, an incident window 19 through which a light source can enter from the outside into the vacuum chamber is disposed at a position of 45 ° with respect to the vertical axis of the vacuum chamber 33, and a scanning optical system is disposed outside the vacuum chamber. The arrangement is arranged. In FIG. 5, a scanning optical system (exposure means) 34 has a light source section, a scanning lens, synchronization detection means, an optical deflector (polygon scanner 35 in the figure), and the like.
The optical housing 36 that holds the scanning optical system may be configured to cover the entire scanning optical system with a cover 37 and shield external light (harmful light) incident on the inside of the vacuum chamber.

The scanning lens has an fθ characteristic, and when the optical polarizer is rotating at a constant speed, the light beam moves at a substantially constant speed with respect to the image plane. Further, the beam spot diameter can be scanned substantially uniformly.
Since the scanning optical system is arranged away from the vacuum chamber 33, the vibration generated when driving an optical deflector such as a polygon scanner is less affected by being directly transmitted to the vacuum chamber. Further, although not shown in FIG. 5, if a damper is inserted between the structure 38 and the vibration isolation table 39, a more effective vibration isolation effect can be obtained.
In FIG. 5, reference numeral 40 is a folding mirror, 41 is an external light shielding cylinder, 42 is a labyrinth section, 43 is a light shielding member, 44 is an internal light shielding cylinder, 45 is an electron gun, 46 is a detector, 47 Indicates a sample, 48 indicates a vacuum sample stage portion, and 49 indicates a scanning beam.
When conducting a latent image experiment, various evaluations can be performed by determining the scanning frequency and linear velocity from the required writing density and using the beam spot diameter, exposure energy, and the like as parameters.

Next, FIG. 6 shows an example of a latent image pattern when two beams are scanned. (A) is a case of 1 dot lattice, (b) is a case of 2 dots isolated, (c) is a case of 2by2, and (d) is a case of 2 dot lines.
By scanning a plurality of light beams in this way, a two-dimensional latent image pattern can be formed.
The two-beam interval is configured such that the interval can be adjusted appropriately by rotating the two-beam light source unit with respect to the reference plane or one of the optical axes (FIG. 2B).
This makes it possible to form various latent image patterns and facilitates correspondence with actual toner images.

Next, FIG. 8 shows an embodiment in which an image pattern of 3 beams or more is formed.
For example, when a 1200 dpi resolution (about 21 μm) latent image is formed in a measurement area of 2 mm square, a latent image pattern of 100 × 100 dots can be formed.
In this way, various latent image images can be formed by a plurality of LDs and image patterns, and the latent image state in a state closer to a real machine can be measured. As a result, when there is a variation in the toner adhesion amount after conventional development, it is determined whether this is a phenomenon that has occurred in the process of development, transfer, or fixing, or whether the latent image has already varied in the state before development. It becomes possible to do.
As a result, it can help to optimize process conditions and optical parameters.

By the way, the latent image area correlated with the toner adhesion amount varies slightly depending on conditions such as uneven charging, photoreceptor sensitivity, electrostatic characteristics, and electrostatic fatigue. It is preferable to calculate the area variation for each latent image pattern as a scale for evaluating it.
A method for calculating the degree of variation in the latent image area when n latent image patterns are formed will be described.
n: number of latent image patterns, <S>: average latent image area, Si: i-th latent image area. The analysis flow at that time is shown in FIG. An example of a latent image pattern with N = 12 is shown in FIG.
The analysis flow is as follows.
(1) A plurality of latent image patterns are formed by the above method.
(2) The electrostatic latent image is measured by the above method, and the latent image is captured. Here, it is the image processing means 51 shown in FIG. 1 that measures the electrostatic latent image.
(3) Each latent image pattern is extracted by image processing such as binarization processing and contour extraction. The extraction of the latent image pattern is performed by the control unit 20 as an extraction unit.
When the captured image has a lot of noise such as density unevenness or abnormal signal, processing such as smoothing or background separation may be performed.
(4) The latent image area Si is measured for each of the plurality of latent images.
The latent image area can be calculated by counting the number of pixel data in the extracted region by image processing such as binarization processing or contour extraction. Alternatively, each latent image pattern may be approximated to an elliptical shape, and the major axis and minor axis diameters may be calculated to calculate the elliptical area. The latent image area is calculated by the latent image area calculating means 52 as the calculating means shown in FIG.
(5) An average latent image area <S> is calculated.
(6) The variation of the latent image area is calculated.

As a method of calculating the degree of variation of the latent image area, it is preferable to calculate an area difference or an area ratio by comparing the average latent image area <S> with each latent image pattern.
In this case, the calculation of variation is performed by the control unit 20 as a comparison unit. The control means 20 may also serve as the signal processing means 50, the image processing means 51, and the latent image area calculation means 52.
Further, a method of calculating the dispersion of the latent image area and the standard deviation may be used. The latent image area standard deviation is expressed as follows.

As the exposure conditions, it is ideal that the same latent image is originally formed if the light beam spot diameter, the image plane light amount, the lighting time, or the duty is constant, but it is actually different.
In addition to the influence of the charging condition and the photosensitive member condition, the exposure condition side has an influence of reciprocity failure.
That is, it also varies depending on the timing time difference when the light is applied and the latent image pattern.
In order to evaluate these, a plurality of latent image patterns are formed under the charging conditions of exposure conditions, image plane light quantity, duty, and beam diameter fixed conditions, and the degree of variation in latent image pattern area at that time is calculated. Thus, the latent image forming ability from charging exposure to latent image formation can be evaluated.

In order not to affect the image density unevenness, the latent image area standard deviation is desirably 10% or less when the light beam spot diameter is 30 to 80 μm.
Needless to say, this latent image pattern evaluation is not limited to the case of one dot, but can be similarly applied to evaluation in which one latent image pattern is formed by a plurality of exposures such as 2by2.
FIG. 9 shows LD light emission conditions for a latent image of a 1-dot lattice.
Condition 1 is an image pattern when LD1 and LD2 are scanned with the same light deflection surface. Condition 2 is that only LD1 is lit on the first surface of the light deflection surface, OFF in LD2, and the second surface of the light deflection surface. In this embodiment, LD1 is OFF and only LD2 is lit.
Even in an optical scanning device mounted in an actual image forming apparatus, the light emission timing of the light beam may differ depending on the light deflection surface, and an electrostatic latent image can be measured under such conditions.
This makes it possible to analyze and evaluate the reciprocity failure phenomenon.

As shown in FIG. 10A, a light beam emitted from a light source unit 22 including a semiconductor laser is deflected and scanned by a polygon mirror 27 via a collimating lens 23, a cylinder lens 25, and a folding mirror 26, and a scanning lens 28, 29. An image is formed on the photosensitive member 17 as a scanned medium by the folding mirror 55.
Print data for one line corresponding to each light emission point is stored in a buffer memory in the image processing apparatus that controls the light emission signal at each light emission point. The print data is read for each deflecting / reflecting surface of the polygon mirror 27, the light beam blinks on the scanning line on the scanned medium corresponding to the printing data, and an electrostatic latent image is formed according to the scanning line. .
Examples of the multi-beam scanning unit are shown in FIGS.
In the configuration example shown in FIG. 10B, the semiconductor laser array 22 in which four light sources are arranged is arranged in the direction perpendicular to the optical axis of the collimating lens 23.
FIG. 10C shows a configuration example of a light source unit of an optical scanning device including a surface emitting laser in which light emitting points are arranged in a plane in the x-axis direction and the y-axis direction. This configuration example is an example using a surface emitting laser 22 having a total of 12 light emitting points, 3 in the horizontal direction (main scanning direction) and 4 in the vertical direction (sub scanning direction). By applying this configuration example to the optical scanning device shown in FIG. 10A, scanning is performed by three light sources arranged in the horizontal direction on one scanning line, and four scanning lines in the vertical direction are simultaneously scanned. Can be configured.

By the way, it has been found that the latent image area is different depending on the surrounding latent image pattern even if the light beam spot diameter, the image surface light amount and the lighting time are constant as the exposure conditions. In particular, it has been found that the peripheral image influences the latent image pattern. This is because whether the peripheral potential is high or low affects the electric field strength at that location, that is, the toner adhesion amount differs.
Therefore, even if the light beam spot diameter and the exposure energy density are constant, the latent image diameter and the latent image area are strictly different between the periphery and the center. In order to solve this, it is desirable to appropriately set the exposure energy condition at that position in consideration of the peripheral image pattern.

FIG. 11 shows the relationship between the exposure lighting time and the latent image area. It is assumed that the image plane light quantity, beam diameter, and charging / photosensitive member conditions are constant. (A) is a latent image of an isolated dot whose periphery is not exposed, and (b) is a latent image exposed with 1 by1. When the LD lighting time is constant, the latent image is formed deeper in (a) than in the state (b), and the latent image area is formed larger. Therefore, in order to obtain the same latent image area, it is preferable to set the exposure energy density of one isolated dot low by shortening the lighting time. Alternatively, the amount of image surface light may be reduced by PM modulation.
Thus, by changing the exposure energy for each dot so that the latent image diameter of the latent image pattern is constant, a high-quality optical scanning device can be provided.
This becomes prominent when it is a high density condition such as 1200 dpi or 2400 dpi. Therefore, it is particularly effective for a high-density or small-diameter optical scanning device, and high-precision and high-speed optical scanning is possible.

An embodiment (laser printer) of an image forming apparatus according to the present invention will be described below with reference to FIG. The laser printer 100 has a “cylindrical photoconductive photosensitive member” as the image carrier 111. Around the image carrier 111, a charging roller 112 as a charging unit, a developing device 113, a transfer roller 114, and a cleaning device 115 are provided.
In this embodiment, a contact-type charging roller 112 that generates less ozone is used as the “charging means”, but a corona charger that uses corona discharge can also be used as the charging means. Further, an optical scanning device 117 is provided to perform “exposure by optical scanning of the laser beam LB” between the charging roller 112 and the developing device 113.

  In FIG. 14, reference numeral 116 denotes a fixing device, 118 denotes a paper feed cassette, 119 denotes a registration roller pair, 120 denotes a paper feed roller, 121 denotes a conveyance path, 122 denotes a paper discharge roller pair, and 123 denotes a paper discharge tray. When forming an image, the image carrier 111, which is a photoconductive photosensitive member, is rotated at a constant speed in the clockwise direction, and the surface thereof is uniformly charged by the charging roller 112. An electrostatic latent image is formed by the exposure by engraving. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed.

This electrostatic latent image is reversely developed by the developing device 113, and a toner image is formed on the image carrier 111. The paper feed cassette 118 containing the transfer paper is detachable from the main body of the image forming apparatus 100, and the uppermost sheet of the stored transfer paper is fed by the paper feed roller 120 when mounted as shown in the figure. . The fed transfer paper is nipped between the registration roller pair 119 at its leading end. The registration roller pair 119 feeds the transfer paper to the transfer unit at the same timing as the toner image on the image carrier 111 moves to the transfer position. The transferred transfer paper is superimposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer roller 114.
The transfer paper on which the toner image has been transferred is fixed on the toner image by the fixing device 116, passes through the conveyance path 21, and is discharged onto the paper discharge tray 123 by the paper discharge roller pair 122.
After the toner image is transferred, the surface of the image carrier 111 is cleaned by the cleaning device 115 to remove residual toner, paper dust, and the like.
By using an optical scanning device and a latent image carrier designed based on the evaluation by the electrostatic latent image evaluation apparatus according to the present invention, an image forming apparatus having excellent resolving power, high definition, high durability and high reliability is manufactured. can do.

It is a schematic block diagram of the electrostatic latent image evaluation apparatus which concerns on one Embodiment of this invention. (A) is an outline top view of an embodiment of an optical scanning device, and (b) is a perspective view of a light source part. It is a schematic block diagram of the modification of an electrostatic latent image evaluation apparatus. It is a figure which shows the relationship between the light source light emission conditions of 1 beam, and a latent image pattern. It is a schematic block diagram of another modification of an electrostatic latent image evaluation apparatus. It is a figure which shows a latent-image image pattern when scanning 2 beams. It is a principle model diagram of charge distribution / potential distribution detection by secondary electrons. It is a figure which shows a latent-image image pattern when scanning 3 beams or more. It is a figure which shows the exposure conditions and latent image pattern from which light emission timing differs. (A) is a perspective view of an embodiment of an optical scanning device, (b), (c) is a perspective view of a light source unit. It is a figure which shows the exposure conditions and latent image pattern from which light emission timing differs. It is a flowchart of latent image area calculation. It is a latent image pattern figure in the case of N = 12. 1 is a schematic configuration diagram of an embodiment of an image forming apparatus. It is a figure which shows the relationship between a beam spot diameter and a latent image diameter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrostatic latent image evaluation apparatus 2 Irradiation means 3 Exposure means 5 Detection means 17 Photoconductor sample 20, 21 Light emission control means 20 Extraction means 20 Comparison means 20, 21 Exposure control means 22 Light source 27 Light deflection means 30 Synchronization detection means 51 Measurement Means 52 Calculation means

Claims (10)

In a method of irradiating a photoconductor sample having a surface charge distribution or a surface potential distribution with a charged particle beam and measuring an electrostatic latent image of the photoconductor sample by a detection signal obtained by the irradiation,
Forming a plurality of latent image patterns on the photoconductor sample, capturing an electrostatic latent image measured by the measurement method as an image, extracting each latent image pattern, and evaluating variations of the plurality of latent image patterns; A method for evaluating an electrostatic latent image characterized by:   An irradiating means for irradiating the photosensitive sample with a charged particle beam; a detecting means for detecting a signal of a charged particle obtained by the irradiation; a measuring means for measuring a state of charge distribution of the photosensitive sample; An electrostatic latent image evaluation apparatus comprising: an exposure unit for forming a plurality of latent image patterns on a photoconductor sample; and a light emission control unit for controlling light emission of a light source of the exposure unit. In the electrostatic latent image evaluation apparatus according to claim 2,
Extracting means for extracting the latent images of the plurality of latent image patterns acquired by the measuring means for each latent image pattern, calculating means for calculating the latent image area of each latent image pattern, and calculating by the calculating means Comparing means for comparing the measured latent image areas, an electrostatic latent image evaluation device. In the electrostatic latent image evaluation apparatus according to claim 3,
The exposure means has exposure control means for forming a plurality of latent image patterns by fixing the image surface light amount, lighting time, and beam diameter, and the calculation means calculates the dispersion of the latent image pattern area at that time. An electrostatic latent image evaluation device. In the electrostatic latent image evaluation apparatus according to claim 2,
A latent image pattern is formed on the photosensitive sample in a vacuum chamber, and the exposure unit is disposed outside the vacuum chamber. In the electrostatic latent image evaluation apparatus according to claim 2,
The exposure unit includes a scanning optical system that deflects and scans light beams from a plurality of light sources by a light deflecting unit, and a synchronization detection unit that detects the scanning beams from the light deflecting unit. Latent image evaluation device. In the electrostatic latent image evaluation apparatus according to claim 6,
In order to form a plurality of latent image patterns, scanning is performed on different light deflection surfaces of the light deflection means, and the electrostatic latent image evaluation device. In an optical scanning apparatus that scans a photosensitive member with a plurality of light beams emitted from a light source via an optical scanning element including an optical deflection unit,
An optical scanning device comprising exposure control means for changing an exposure energy density applied to the photoconductor according to a peripheral latent image pattern. The optical scanning device according to claim 8.
The exposure control means controls the exposure conditions so that the exposure energy density is set lower in the latent image formation of the isolated dots in which the neighboring area is not exposed than in the latent image formation in which the neighboring area is exposed. An optical scanning device.   An image forming apparatus, wherein a latent image is formed by scanning a photosensitive member using the optical scanning device according to claim 8, developed, and visualized.

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