JP2005283712A - Charging apparatus, electrostatic latent image forming apparatus, image forming apparatus, and electrostatic latent image measurement device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize high image quality, high durability, high stability, etc., by measuring electrostatic latent image on a photoreceptor, within a short time after the formation of a latent image in an electrophotographic system, and by providing feedback on design, the quality for each process is improved. <P>SOLUTION: An electron beam B generated from an electron gun 1 is converged by an electronic condenser lens 2, passes through a scanning lens 4 and an objective lens 5, and scans the inside of the electrified area of a sample 6. The sample 6 is charged to a predetermined potential according to the relation between a back potential Vg applied to a conductor 7 and an acceleration voltage. A light beam L, emitted from a light source 10, such as an LD, is emitted to the sample 6 via a collimating lens 11, a cylinder lens 13, etc., and forms an electrostatic latent image on the sample 6. By stopping the light emission, changing the conditions again, and scanning with an electron beam, an output corresponding to the latent image can be obtained in a charge detector. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrostatic latent image forming apparatus and an electrostatic latent image measuring apparatus in an electrophotographic process. Further, the present invention relates to a technique that can be applied to a measuring method and apparatus for surface potential distribution, surface electric field distribution, and surface charge distribution of a dielectric sample.

In order to obtain an output image in an electrophotographic system such as a copying machine or a laser printer, the process factor and process quality in each process greatly affect the final output image quality. In recent years, in addition to high image quality, there has been an increasing demand for environmentally friendly imaging processes such as high durability, high stability, and energy saving, and it is necessary to improve the process quality of each process. For the image forming process, the electrostatic latent image on the photoreceptor accompanying exposure is a factor that directly affects the behavior of the toner particles, and it is necessary to grasp the behavior. For this reason, it is extremely important to evaluate the quality of the electrostatic latent image on the photoreceptor.
By measuring the electrostatic latent image of the photoreceptor and feeding it back to the design, the process quality of each process is improved. As a result, high image quality, high durability, high stability, and further energy saving can be expected.
However, at present, the electrostatic latent image is not measured at all, rather than being extremely difficult to measure.

As a method for observing an electrostatic latent image using an electron beam, there is Patent Document 1, but the sample is limited to an LSI chip or a sample that can store and hold an electrostatic latent image. 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 photoconductor, 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 an electron microscope (SEM) after charging and exposure, the electrostatic latent image disappears at the preparation stage.
Therefore, the present inventor has means for irradiating a charged particle beam to form an electrostatic latent image in an apparatus for performing measurement, and performing the measurement within a short time after the latent image is formed. The image distribution can be measured (for example, see Patent Document 2).

JP 03-49143 A JP 2003-295696 A

  In the method shown in Patent Document 2, it is necessary to change the acceleration voltage of incident electrons in order to control the charging potential, but it is difficult to control the acceleration voltage in fine steps. Further, in order to generate a high charging potential, it is necessary to increase the set voltage, which requires large power consumption. In addition, when the electrostatic latent image is measured, there is a problem that the acceleration voltage at the time of observation must be changed if the charging potential is different.

According to the first aspect of the present invention, there is provided a charging device that generates a charged charge on the sample by irradiating the sample with negative charged particles such as electrons or negative ions, the surface for charging the sample. When the surface opposite to the surface (hereinafter referred to as the back surface) is in a grounded state, an acceleration voltage of electrons that gives a secondary electron emission ratio of 1 is E ₀ (> 0), and a voltage for accelerating the charged particles is E ₁ (> 0), when the back surface potential applied to the back surface is Vg,
E ₁ > E ₀ -Vg
A desired negative charging potential is formed on the sample under the following conditions.

According to a second aspect of the present invention, in the charging device according to the first aspect, when the desired charging potential is Vs, | E ₁ −E ₀ + Vg | ≧ | Vs |
A back surface potential Vg that satisfies the following condition is applied.
According to a third aspect of the present invention, in the charging device according to the second aspect, the back surface potential Vg is further
| E ₁ −E ₀ + Vg | ≦ | Vs | +2 kV
It is characterized by satisfying.

According to a fourth aspect of the present invention, in the charging device according to any one of the first to third aspects, the charged charge is generated in a vacuum.
According to a fifth aspect of the present invention, in the charging device according to any one of the first to fourth aspects, the back surface potential Vg is set to a ground state after the generation of the charged charge is completed.
According to a sixth aspect of the present invention, in the charging device according to any one of the first to fifth aspects, the back surface potential Vg has means for setting a spatially different value with respect to the sample. Features.

According to a seventh aspect of the present invention, the charging device according to any one of the first to sixth aspects and an exposure optical system are provided, and the surface of the charged sample is irradiated by the exposure optical system. Then, an electrostatic latent image is formed on the surface of the sample by charge distribution.
The invention according to claim 8 is characterized in that the electrostatic latent image forming apparatus according to claim 7 is used.

According to a ninth aspect of the invention, there is provided the electrostatic latent image forming apparatus according to the seventh aspect, further comprising measuring means for measuring the electrostatic latent image on the sample surface by scanning the sample surface with an electron beam. It is characterized by that.
According to a tenth aspect of the present invention, in the electrostatic latent image measuring apparatus according to the ninth aspect, the measuring means detects emitted electrons from the sample.

  According to the present invention, the sample can be efficiently charged to a desired potential by appropriately setting the back surface potential Vg.

FIG. 1 is a diagram showing an embodiment of the present invention.
In the figure, reference numeral 1 is an electron gun, 2 is a condenser lens, 3 is a beam blanker, 4 is a scanning lens, 5 is an objective lens, 6 is a sample such as a photoreceptor, 7 is a conductor, 100 is a charged particle irradiation unit, and 200 is A sample placement part B represents an electron beam or an ion beam, respectively.
The present embodiment includes a charged particle irradiation unit 100 that irradiates a charged particle beam and a sample setting unit 200.
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 100 includes an electron gun 1 for generating an electron beam, a condenser lens 2 for focusing the electron beam generated from the electron gun 1, and a beam blanker 3 for turning the electron beam on and off (see FIG. And an electron optical system such as a scanning lens 4 for scanning the charged region with an electron beam and an objective lens 5 for condensing the scanning lens again. A driving power source (not shown) is connected to each lens. When the beam diameter corresponds to the charged region, the scanning lens 4 may not be provided.
A potential Vg can be applied to the surface opposite to the surface on which the sample is charged. The electron optical system and the sample portion are arranged in a vacuum so that electrons travel on an accurate trajectory.

The photoconductor sample 6 is irradiated with an electron beam B. Acceleration voltage E _{1 (>} 0), by secondary electron emission ratio δ is set to an acceleration voltage E _{0 (> 0)} than the high acceleration voltage of 1, electronic the incident electron amount is greater than than the amount of emitted electrons Accumulates in the sample and causes charge up. As a result, the sample 6 can be negatively charged. By appropriately performing the acceleration voltage and the irradiation time, a desired charging potential can be formed.
Here, the secondary electron emission ratio δ is
δ = emitted electron / incident electron, but more strictly speaking, it is necessary to consider transmitted and reflected electrons.
Emission electron = transmission electron + reflection electron + secondary electron is preferable. Note that when the lower surface of the sample is grounded (GND), the acceleration voltage of electrons at which the secondary electron emission ratio of the sample is 1 is E ₀ . E ₀ corresponds to the charging start voltage.

FIG. 2 is a diagram showing the relationship between the acceleration voltage and charging.
FIG. 3 is a diagram showing the relationship between the electron beam irradiation time and the charging potential.
FIG. 4 is a diagram showing the relationship between the acceleration voltage and the charging potential.
The secondary electron emission ratio δ depends on the energy of the electron beam, that is, the acceleration voltage, and generally has a relationship as shown in FIG. At an acceleration voltage E ₁ (> 0) at which δ = 1, charging does not occur and an equilibrium state is maintained. In the case of the acceleration voltage E ₁ > E ₀ , δ <1 and the number of emitted electrons is smaller than the number of incident electrons, so that negative charging is performed.
FIG. 3 shows the relationship between the acceleration voltage and the irradiation time. Immediately after the electron beam irradiation, charges are rapidly accumulated, but as time passes, incident electrons are decelerated due to the negatively charged potential of the sample. In the surface potential potential Vp (> 0), when the velocity (landing velocity) when the electrons reach the surface is v, the mass of the electrons and the charge amount are m and e, respectively,
v = {2e (E ₁ + Vp)}} ^1/2 (1)
Can be expressed approximately. Therefore, with the charge accumulation (negative charge), the landing speed decreases, the charge accumulation amount per unit time decreases, and E ₁ + Vp = E _0, that is,
Vp = E ₀ −E ₁ (2)
In this condition, the equilibrium stable state is reached, and no further charging occurs, that is, the saturation charging potential Vd is reached. An example of the relationship between the saturation charging potential and the acceleration voltage is shown in FIG.

The potential potential Vp on the surface is the sum of the potential Vs generated by the sample surface charge density Qs and the potential Vg on the surface opposite to the sample charge accumulation surface, that is, Vp = Vs + Vg (3)
It can be expressed as
However, Vs = Q / C = d / (S × ε ′ × ε0) × Qs
ε ′: relative dielectric constant, ε0: vacuum dielectric constant, Q: charge accumulation amount, S: unit area, d: sample thickness Here, since the characteristic value of the sample may be considered constant,
The relationship Vs Ｑ Qs is established.

FIG. 5 is a diagram showing a measurement result according to the present invention.
By applying and controlling the voltage Vg to the lower part of the sample, the back surface, etc., the potential Vs generated by the sample surface charge density Qs can be controlled.
The figure shows the measurement result of the saturation charging potential when the acceleration voltage is constant at 1.5 kV and the potential Vg on the lower surface of the sample is changed. At the measurement result, Vg = 0V. The unit is (-V). When Vg = 0V, the potential is −550V, and as a result, E _{0 of} this sample is −950V. When Vg is changed to the plus side, the incident electrons are relatively accelerated and easily charged, the charge accumulation amount is increased, and the charged potential is increased in the minus direction. Further, when Vg is changed to the minus side, the incident electrons are relatively decelerated and become difficult to be charged, the charge accumulation amount is reduced, and the charging potential is lowered. The relationship between the charging potential and the applied voltage is approximately established by the following relational expression.
Saturation charging potential Vd (-V)
= Acceleration voltage E ₁ (V) −Charge start voltage E ₀ (V) + Applied voltage Vg (V) (4)
Therefore, if the conventional Vg = 0, even a sample that could only be charged up to -550V with an acceleration voltage of 1.5kV can be charged to -850V by applying a voltage of Vg = 300V. is there. By applying a higher voltage to Vg, a higher charging potential can be obtained.

Since the charge accumulation amount changes with time as shown in FIG. 3, by controlling Vg and charging time, | E ₁ −E ₀ + Vg | ≧ | Vs |
It is possible to obtain a charging potential Vs that satisfies the following condition.
Compared to the conventional technology, the acceleration voltage can be kept low. Therefore, the power consumption is low and the environment is friendly, and the control is easy.
When the acceleration voltage is increased, the time to reach the target charged potential is shortened, so that it becomes difficult to control and damage to the sample cannot be ignored. Therefore, it is desirable that the desired charging potential can be formed with as small an acceleration voltage as possible.
| Vs | ≦ | E ₁ −E ₀ + Vg | ≦ | Vs | +2 kV (5)
Is appropriate.
In this sample (E ₀ = −950V), in order to charge Vs = −800V, when Vg = 0, E ₁ = 1.75-3.75 kV is an appropriate range, but Vg = 750V By setting, it can be realized with an acceleration voltage as low as E ₁ = _{1 to 3} kV.
In order to charge in a short time, the current density of the electron beam may be increased.
The charging means by applying the lower voltage can also be applied in the atmospheric charging method, but if it is in a vacuum, charged particles are not subject to interference by atmospheric particles, so that highly accurate charge formation can be performed.

FIG. 6 is a diagram for explaining an example of latent image formation and measurement.
FIG. 7 shows an example of an exposure optical system.
In FIG. 6, reference numeral 10 denotes a light source, 11 denotes a collimating lens, 12 denotes an aperture, 13 denotes a cylinder lens, 14 denotes a scanning lens, 15 denotes an LD control unit, 16 denotes a charge detector, and 300 denotes an exposure optical system.
In FIG. 7, reference numeral 20 is a light source, 21 is a collimating lens, 23 is a cylinder lens, 24 is a scanning lens, 26 is a first folding mirror, 27 is a polygon mirror, 28 is a second folding mirror, and 29 is a photosensitive drum. Each is shown.
The latent image forming means will be described.
After the photoconductor sample 6 is charged by a predetermined amount, the photoconductor sample 6 is exposed by the exposure optical system 300.
The exposure optical system 300 is adjusted so as to form a desired beam diameter and beam profile. It comprises a light source 10 such as an LD (laser diode) having a wavelength in the sensitivity range of the photoconductor sample 6, a collimate lens 11, an aperture 12, a cylinder lens 13, a scanning lens 14, and the like. Generate a profile. An appropriate exposure time and exposure energy can be irradiated by the LD control unit 15.
As shown in FIG. 7, by adding a scanning mechanism using a polygon mirror 27, an arbitrary latent image pattern including a line pattern can be formed in the generatrix direction of the photosensitive drum 29.
Thereby, an electrostatic latent image can be formed on the photoreceptor sample.

The condition is changed to the electrostatic latent image of the photoconductor sample, and the electron beam is scanned again. The emitted secondary electrons are detected by the charge detector (scintillator) 16, converted into an electric signal, and the potential contrast image is measured. .
If there is a charge distribution on the sample surface, an electric field distribution corresponding to the 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 16 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. When exposed, the exposed area is black and the non-exposed area is white. Therefore, the electrostatic latent image formed can be measured by scanning the sample surface with the electron beam and detecting the signal thereby.
The signal intensity on the detector may be corrected when it changes depending on the setting conditions. Further, calibration may be performed in advance. Moreover, you may detect a reflected electron instead of a secondary electron.
After the measurement is completed, residual charges can be removed by irradiating the entire sample surface with an LED or the like.
FIG. 6 shows the configuration of the control unit of the present invention.

FIG. 8 is a diagram for explaining an embodiment for measuring an electrostatic latent image of a cylindrical photosensitive member.
In the chamber, a cylindrical photoconductor sample 29, a charging unit 30 for irradiating the periphery of the photoconductor sample, an exposure unit 31 for forming a charge distribution, and a charge eliminating unit for erasing the charge. There are 32.
The photosensitive member 29 is attached with driving means that can rotate with respect to the central axis of the photosensitive member. Examples of the driving means include a stepping motor and a DC servo motor.
As charging means of the charging unit 32, there are charge injection charging such as charging by electron beam irradiation and contact charging.
There exist LED etc. as a static elimination part.

As an operation in this case,
1. The charging unit is configured to be able to apply a voltage Vg on the inner side of the photoconductor, that is, on the side opposite to the charging surface, and the photoconductor so that the surface of the photoconductor is at a desired potential with the voltage Vg applied. Is uniformly charged.
2. The voltage applied to the lower electrode of the photosensitive member is set to the ground state (GND).
3. In the exposure unit, the photosensitive member is irradiated with light to partially release the charges and form an electrostatic latent image.
4). In the measurement unit, the photosensitive member sample is scanned with an electron beam, and the emitted electrons are detected with a scintillator, converted into an electric signal, and a potential contrast image is observed.
5). In the static elimination unit, residual charges on the photoreceptor are erased by irradiating the LED or the like.
By using such a method, it is possible to measure the electrostatic latent image of the photoreceptor even in the cylindrical shape.
Although the applied voltage of the lower electrode of the photosensitive member is set to the ground state (GND), the voltage may be kept applied depending on the image forming means.

FIG. 9 is a diagram for explaining another embodiment.
In the figure, the symbol P indicates a counter electrode.
Since the photosensitive drum 29 as the dielectric portion rotates and the conductive portion to be applied is fixed, an independent voltage can be applied by providing a counter voltage for each application process.
The counter electrode P is fixed corresponding to the peripheral device of the photoconductor.
FIG. 10 is a diagram for explaining still another embodiment.
In the figure, the symbol p indicates a conductor portion forming a counter electrode.
By providing a gap in the insulating portion between the inner conductor portion p and the conductor portion p, it is possible to apply a desired voltage independent of each process. In this case, the conductor part p may be fixed corresponding to the peripheral device, or may be rotated integrally with the photoconductor.
FIG. 11 is a diagram for explaining still another embodiment.
12 and 13 are diagrams for explaining the charging means. FIG. 12 shows a corotron charger, and FIG. 13 shows a scorotron charger.
FIG. 14 is a diagram showing a photosensitive peripheral device used in a normal image forming apparatus.
A latent image is measured in a vacuum by charging in the atmosphere and using a differential pumping mechanism. As the atmospheric charging means, corona discharge can be used, and corotron charging and scorotron charging can also be used as shown in FIGS. 12 and 13. An effect can be obtained. In this case, the amount of ozone generated is small and environmentally friendly. Note that this charging method may be applied to a normal image forming apparatus as shown in FIG.

If the sample is a dielectric, the latent image forming unit may be a system that directly forms a charge distribution, such as an electrostatic recording system. In the case where the sample is a photoconductor, the latent image forming unit may be composed of a charging unit and an exposure unit.
When the sample is a cylindrical photoconductor, the configuration shown in FIG. 11 can be used.
By using such a method, it is possible to measure the electrostatic latent image on the photoreceptor in a state close to the actual use environment. In addition, it is possible to measure the distribution state of the electrostatic latent image of several hundred ms or less corresponding to the process speed.

It is a figure which shows the Example of this invention. It is a figure which shows the relationship between an acceleration voltage and charging. It is a figure which shows the relationship between the irradiation time of an electron beam, and a charging potential. It is a figure which shows the relationship between an acceleration voltage and a charging potential. It is a figure which shows the measurement result by this invention. It is a figure for demonstrating the example of latent image formation and a measurement. It is a figure which shows an example of an exposure optical system. It is a figure for demonstrating the Example which measures the electrostatic latent image of a cylindrical-shaped photoreceptor. It is a figure for demonstrating another Example. It is a figure for demonstrating another Example. It is a figure for demonstrating another Example. It is a figure for demonstrating a charging means. It is a figure for demonstrating a charging means. FIG. 3 is a diagram illustrating a photoreceptor peripheral device used in a normal image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electron gun 2 Condenser lens 4, 14, 24 Scan lens 6 Sample 10, 20 Light source 11, 21 Collimate lens 15 LD control part 27 Polygon mirror 29 Photosensitive drum

Claims (10)

A charging device for generating a charged charge on the sample by irradiating the sample with negative charged particles such as electrons or negative ions, the surface opposite to the surface for charging the sample (hereinafter referred to as a back surface) referred) is E the acceleration voltage of electrons secondary electron emission ratio is 1 when the ground state _{0 (>} 0), the voltage for accelerating the charged particles E _{1 (>} 0), the back surface When the back surface potential applied is Vg,
E ₁ > E ₀ -Vg
A charging device, wherein a desired negative charging potential is formed on the sample under the following conditions. 2. The charging device according to claim 1, wherein when the desired charging potential is Vs, | E ₁ −E ₀ + Vg | ≧ | Vs |
A charging device characterized by providing a back surface potential Vg that satisfies the following conditions. The charging device according to claim 2, wherein the back surface potential Vg is further
| E ₁ −E ₀ + Vg | ≦ | Vs | +2 kV
A charging device characterized by satisfying   4. The charging device according to claim 1, wherein the generation of the charged electric charge is performed in a vacuum. 5.   5. The charging device according to claim 1, wherein the back surface potential Vg is set to a grounded state after the generation of the charged charge is completed. 6.   6. The charging device according to claim 1, further comprising means for setting the back surface potential Vg to a spatially different value with respect to the sample.   A charging device according to claim 1, and an exposure optical system, wherein the surface of the sample charged by the exposure optical system is irradiated with light to distribute the charge on the surface of the sample. An electrostatic latent image forming apparatus, characterized in that an electrostatic latent image is formed.   An image forming apparatus comprising the electrostatic latent image forming apparatus according to claim 7.   8. The electrostatic latent image forming apparatus according to claim 7, further comprising measuring means for measuring the electrostatic latent image on the sample surface by scanning the sample surface with an electron beam. apparatus. 10. The electrostatic latent image measuring apparatus according to claim 9, wherein the measuring unit detects electrons emitted from the sample.

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