JPH06258368A - Surface potential measuring device - Google Patents

Abstract

PURPOSE:To obtain high sensitive and precision measurement by making an optical element, containing electro-optical effect, enduce electric charge corresponding to a detection part of an object to be measured, making light beam incident for measurement of out-going light quantity, performing Fourier transformation with the surface potential distribution of the object, while correction being made with broadening function of measuring area, and performing invert Fourier transformation. CONSTITUTION:Light beam L from a light source 26 is diffracted at an input diffraction grating 20, and it comes into an optical wave guide 14. In measuring the surface potential of an object S to be measured, the charged voltage of the object S is, through a probe 24, applied to a grid-like electrode 18, and the wave guide 14 is applied with the voltage corresponding to that, and its refractivity is changed by electro-optical effect for generation of a diffraction grating. The diffraction light and straight advance light of beam L, caused by that, is diffracted at an output diffraction grating 22, for out-going, and measured by a control part 38, to be outputted as a surface potential distribution. A calculation part 33 performs Fourier transformation with the result, then makes correction using a correction function generated from a spreading function of a measuring system, and then with the obtained correction data, invert Fourier transformation is made, so that the corrected result of surface potential distribution is calculated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring the surface potential of a charged body such as an electrophotographic photosensitive member on which an electrophotographic electrostatic latent image is formed. Specifically, the present invention relates to a surface potential measuring device capable of highly accurately and highly sensitively measuring a surface potential.

[0002]

2. Description of the Related Art Electrophotographic image recording is used in various image recording applications such as a plate making apparatus, a copying machine, and a laser plotter.

As is well known, for image recording by electrophotography, an electrophotographic photosensitive member having an optical semiconductor layer and a conductive support layer is used, and the optical semiconductor layer of the electrophotographic photosensitive member is uniformly made by corona charging or the like. After charging, image exposure is performed by light beam scanning, reflected light from the original, etc. to release the charged electric charge of the exposed portion on the optical semiconductor to form an electrophotographic latent image (hereinafter, electrostatic latent image). The electrostatic latent image is visualized by developing with toner charged in the opposite polarity to the electrostatic latent image.

In such an electrophotographic image recording, the basis of the formed image is the above-mentioned electrostatic latent image. To know the state of this electrostatic latent image, it is necessary to know the electrophotographic photosensitive member or the printing image. This is important for evaluating and analyzing individual printing processes (charging, exposure, and development), and also for evaluating and analyzing the entire recording system. Further, in recent years, image quality has been improved even in electrophotographic image recording, and there is an increasing need to measure an electrostatic latent image with high definition (high resolution).

The surface potential distribution of such an electrostatic latent image is conventionally measured by a surface potential meter using an induced current. However, in the surface potential distribution measurement by such a conventional measuring method, the resolution is low, and it is possible to measure only the potential of the entire surface within the range of 1 to 2 mm square. On the other hand, in image recording by light beam scanning, one scanning line (1 raster) is usually about 10 to 100 μm, so it is necessary to measure the surface potential distribution in such a minute portion. Such a measurement cannot be performed and a sufficient measurement result cannot be obtained.

Further, a method of utilizing an electron beam is known as a method of measuring the surface potential distribution with high precision, but this method cannot measure in the air, and also destructive inspection of the electrostatic latent image. In addition, the time from the charging of the electrophotographic photosensitive member to the measurement is long, and it is difficult to measure with an electrophotographic photosensitive member that applies zinc oxide or an organic photosensitive material and has a relatively large dark decay. There is also the problem that there are.

In order to solve such a problem, the applicant of the present invention invented a surface potential measuring device using an optical element having an electro-optical effect as a device capable of measuring the surface potential with high resolution and accuracy. I have proposed this earlier. For example,
In Japanese Patent Application No. 2-224860, a measuring head in which a nonlinear optical crystal is sandwiched between counter electrodes, and an electrostatic shield plate having fine holes between a counter electrode used for measurement and an object to be measured are arranged. Then, the other counter electrode has a configuration in which a bias power supply is provided, and a linearly polarized light beam is made incident on the nonlinear optical crystal, preferably in a direction orthogonal to the facing direction of the counter electrode, We have proposed a surface potential measuring device that measures the surface potential of the object to be measured from the change in the polarization of the light beam that has passed through.

Further, in Japanese Patent Application No. 4-281224, an optical waveguide having an electro-optical effect, a grid electrode formed on the optical waveguide, and a waveguide corresponding to the grid electrode are guided. A light source for injecting a light beam into the optical waveguide, a conductive probe whose one end side is connected to the grid electrode and the other end side is arranged in proximity to the DUT, and the portion corresponding to the grid electrode. And a photodetector for detecting the light quantity of a diffracted light beam or a non-diffracted light beam.

In these surface potential measuring devices, a shield plate which is close to or close to the counter electrode and has fine holes and which is close to the object to be measured, and a probe which is connected to the counter electrode are close to the object to be measured. By inducing a potential corresponding to the surface potential of this measurement region in a crystal having an electro-optical effect, the polarization, phase, and refractive index of the light beam passing through this crystal are changed, and the object to be measured is detected by detecting this. Measure the surface potential of.

In the surface potential measuring device utilizing such an electro-optical effect, the resolution of the surface potential measurement can be adjusted by the tip size of the probe and the size of the fine holes of the shield plate, and the high resolution of about several μm square. It is possible to measure the surface potential at.

[0011]

However, the resolution can be increased by reducing the tip size of the probe and the size of the fine holes of the shield plate, but the sensitivity of the surface potential measurement is also reduced accordingly. Therefore, in order to realize both high resolution and high sensitivity surface potential measurement while achieving both, there is a limit to miniaturization of the probe tip size and the like.

Further, in such a surface potential measuring device, in order to measure the surface potential with high resolution, it is preferable to dispose the object to be measured and the probe or the like as close as possible. However, if the two are brought too close to each other, the surface potential of the measured object leaks even if they are not in contact with each other. Therefore, the measured object is nondestructive, for example, an electrostatic latent image formed on an electrophotographic photoreceptor or the like. In order to perform non-destructive measurement and the like, some distance is required between the object to be measured and the probe or the like. In particular, since the surface potential of an electrostatic latent image formed on an electrophotographic photosensitive member is about several hundreds V, unless the distance between the object to be measured and the probe is kept above a predetermined value, the electrostatic latent image will be formed. Not only is it destroyed, but the measuring head using a crystal having an electro-optical effect is also destroyed.

Therefore, the measurement is performed with a predetermined gap between the object to be measured and the probe, but since there is a distance between them, the electric field detected by the probe from the object to be measured spreads. The measurement value of the surface potential distribution is blurred, and an error occurs in the measurement result of the surface potential distribution, resulting in a decrease in resolution.

An object of the present invention is to solve the above-mentioned problems of the prior art, and realizes extremely high resolution, high sensitivity and high accuracy of measurement as compared with the conventional surface potential measuring device utilizing an induced current or the like. An object of the present invention is to provide a surface potential measuring device using an optical element having an electro-optical effect, which can realize excellent surface potential measurement because of its resolution, sensitivity and accuracy.

[0015]

In order to achieve the above-mentioned object, the present invention provides an optical element having an electro-optical effect, an element electrically contacting the optical element, and an element electrically close to an object to be measured. Electrode, a light source for emitting a light beam incident on the optical element, a measuring unit for measuring the light amount of the light beam emitted from the optical element, and the measured object obtained from the light amount measured by the measuring unit. Fourier transform of the surface potential distribution of the object, after correcting the result of the Fourier transform by the spread function of the measurement region of the measurement system, and then inverse Fourier transform this to obtain a measurement result of the surface potential distribution. A surface potential measuring device is provided.

[0016]

INDUSTRIAL APPLICABILITY The present invention utilizes an optical element having an electro-optical effect such as a non-linear optical crystal, induces a charge corresponding to the detected portion of the charged body in the optical element, and passes the optical element. A surface potential measuring device for measuring the surface potential of a charged body by measuring changes in the polarization, phase, refractive index, etc. of a light beam. The obtained surface potential distribution measurement result is Fourier transformed and Fourier transformed. After correcting the result by the spread function of the measurement region by the measurement system, the result is inverse Fourier transformed to obtain the measurement result of the surface potential distribution.

A surface potential measuring device using an optical element having an electro-optical effect is obtained by adjusting the size of a probe or the like facing an electrified body which is an object to be measured and a distance to the object to be measured which is connected to an electrode. , It is possible to realize surface potential measurement with extremely high resolution, high sensitivity, and high precision as compared with the conventional surface potential meter using induced current. However, there is a limit to the improvement of resolution and sensitivity by these adjustments, and since the measurement is performed without contact with the charged body, the electric field detected by the probe or the like expands and the surface potential is increased. As described above, the measurement result of the distribution is blurred and causes the deterioration of the resolution and the sensitivity.

On the other hand, in the surface potential measuring apparatus of the present invention, the spread of the electric field, that is, the spread of the measurement region by the probe or the like is made into a function, and the measurement result is corrected by using this function and Fourier transform. . Therefore, the surface potential distribution can be measured with high resolution, high sensitivity, and high accuracy without blurring due to the spread of the electric field, and the electrostatic latent image formed on the electrophotographic photosensitive member can be measured with high accuracy. It can be carried out.

[0019]

EXAMPLES Hereinafter, the surface potential measuring device of the present invention will be described.
A detailed description is given based on the preferred embodiments shown in the accompanying drawings.

FIG. 1 is a side view of an example of the surface potential measuring device of the present invention, and FIG. 2 is a conceptual plan view of the same.
The surface potential measuring device 10 (hereinafter referred to as the measuring device 10) shown in FIGS. 1 and 2 basically includes a light source 26 that emits a light beam L as a measurement light and an optical element having an electro-optical effect. The measurement head 30 formed by using the photoelectric conversion element 32, the voltmeter 34, and the output of the voltmeter 34, which constitute the measurement means for measuring the light amount of the light beam L ₁ that has passed through the measurement head 30 and is refracted, It is composed of a control unit 38 having a calculation unit 36 for calculating the potential.

The measuring head 30 is basically a LiNb having an electro-optical effect, which is arranged in the crystal orientation shown in FIG.
O ₃ (lithium niobate) substrate 12 formed on a proton exchange optical waveguide 14 (hereinafter referred to as optical waveguide 14)
A buffer layer 16 made of a SiO ₂ film formed on the optical waveguide 14, a grid electrode 18 formed on the buffer layer 16, and a grid electrode 18 on the optical waveguide 14 in the traveling direction of the light beam L. A linear diffraction grating for optical input (hereinafter, referred to as LGC for input) 20 and a linear diffraction grating for optical output (hereinafter, referred to as LGC for output) 22 that are arranged so as to sandwich the two electrodes, and one end of the grid electrode 18. Are connected to each other, and the other end of the conductive probe 24 is arranged close to the object S to be measured S which is a charged body such as an electrophotographic photoreceptor. In the present embodiment, the conductive probe 24 of the grid electrode 18 (hereinafter,
The end on the side not connected to the probe) is grounded, but a bias potential may be applied depending on the measurement purpose.

In the measuring apparatus 10 of the illustrated example, a light source 26 such as a He-Ne laser that emits a light beam L has an end face 12 in which a light beam L that is parallel light is obliquely cut on a substrate 12.
a and then the optical waveguide 14 and the input LGC 20
It is arranged to be incident on. Therefore, the light beam L emitted from the light source 26 is diffracted by the input LGC 20 and enters the optical waveguide 14, and the optical waveguide 14 is indicated by the arrow A.
Proceed in the direction.

With this progress, the light beam L (guided light) is guided through the portion corresponding to the grid electrode 18 in the optical waveguide 14, but no voltage is applied to the grid electrode 18. Then, the light beam L travels straight in the optical waveguide 14 without being refracted and is emitted from the measuring head 30 as shown by the laser light L ₂ in FIG. On the other hand, when one end of the probe 24 is close to the measured object S when measuring the surface potential of the measured object S, a voltage according to the charging potential of the measured object S is applied to the grid electrode 18, A voltage corresponding to this is applied to the optical waveguide 14. When a voltage is applied to the optical waveguide 14, the optical waveguide 14 having an electro-optical effect changes its refractive index according to the applied voltage, and a diffraction grating corresponding to the grid electrode 18 is formed. It is diffracted by this diffraction grating.

In this manner, the light beam L ₁ diffracted (refracted) in the optical waveguide 14 and the light beam L ₂ (0th order light) that has not been diffracted and travels straight are diffracted downward by the output LCG 22. , Is emitted from the measurement head 30 via the end surface 12b of the substrate 12 that is obliquely cut.

Light beam L ₁ emitted from the measuring head 30
Is measured by the control unit 38 and output as the surface potential measurement result of the object S to be measured. The control unit 38 basically
A photoelectric conversion element 32 such as a photodiode, a voltmeter 34,
It is composed of a calculation unit 36, a power supply 40, and a resistor 42.

In the control unit 38, the light beam L ₁ emitted from the measuring head 30 is received by the photoelectric conversion element 32. One end of the photoelectric conversion element 32 is connected to the power source 40,
The other end side is connected to a voltmeter 34, which constitutes a measuring means together with the photoelectric conversion element 32, and a resistor 42. The voltmeter 34 measures the voltage between the photoelectric conversion element 32 and the resistor 42. This voltage corresponds to the amount of light of the diffracted light beam L ₁ , and this amount of light corresponds to the voltage applied to the grid electrode 18, that is, the surface potential of the measured object S. Therefore, the surface potential of the measured object S can be measured from the measurement result of the voltmeter 34.

The measurement result obtained by the voltmeter 34 is calculated by the calculation unit 36.
Transferred to. The calculation unit 36 calculates the surface potential distribution of the measured object S from the measured value from the voltmeter 34, corrects the calculated surface potential distribution using a correction function and Fourier transform, and calculates the measured surface potential of the measured object S. Output as surface potential distribution. In addition,
In the present invention, the voltmeter 34 may calculate the surface potential distribution of the measured object S and transfer it to the calculation unit 36.

In the measuring system for measuring the surface potential of the object S to be measured and the probe 24 in a non-contact manner like the measuring apparatus 10 of the present invention, the electric field spreads in the gap between the probe 24 and the object S to be measured. That is, the measurement area of the probe 24 is expanded, and even if a complete line is measured, the line width is slightly expanded. In the present invention,
A correction function is created from the spread function of the line image (FIG. 3) in the measurement system of the measurement device 10, and the measurement result is corrected. The spread function of the measuring system of the measuring device 10 as shown in FIG.
nction) can be obtained.

The correction function is created by Fourier-transforming this spread function to obtain a function as shown in FIG. 4 and taking the reciprocal thereof. When the spread function of FIG. 3 is Fourier-transformed, it becomes a function showing the responsivity at each (spatial) frequency of this measurement system as shown in FIG. 4, that is, to which frequency can be separated. In such a non-contact measurement system, due to the spread of the electric field,
Regions above a certain frequency cannot be measured (transmitted) at all. In other words, the area narrower than a certain line width (area with high frequency) cannot be measured.

Here, as described above, the function of FIG. 4 shows the response to the frequency in this measurement system, that is,
It is shown that even if a uniform signal is input in the entire frequency range, such an output signal is obtained at each frequency. Therefore, since the reciprocal of this function should be the original input signal, by taking the reciprocal of this function, it is possible to create a correction function corresponding to the spread of the measurement region in this measurement system.

In the measuring device 10 of the present invention, the correction of the surface potential measurement result using such a correction function is performed as follows. As described above, in the calculation unit 36, the measurement result of the surface potential distribution before correction is obtained from the measurement result of the voltage by the voltmeter 34. Here, the measured object S
Has a surface potential distribution as shown in FIG.
When the measured measurement result before correction is as shown in FIG. 6, the calculation unit 36 Fourier transforms this result, and the horizontal axis as shown in FIG. 7 becomes the frequency. Get the function. The function shown in FIG. 7 is multiplied by the above-mentioned correction function to obtain the correction data 1 as shown in FIG.

Since the function shown in FIG. 4 is 0 above a certain frequency, the correction data 1 shown in FIG. 8 obtained by multiplying the correction function obtained from this is noise in the high frequency region. Has been greatly increased. In order to correct this noise, the correction data 1 is multiplied by a (low-pass) filter as shown in FIG.
The correction data 2 shown in is obtained.

In the measuring apparatus 10 of the present invention, the shape of the filter for correcting the correction data 1 is basically rectangular, but in many cases noise and the like cannot be suitably cut, so cut & error. A good filter may be manufactured by examining a good shape by the above method.
In addition, a few kinds of filters may be prepared and appropriately selected and used according to the purpose.

By inverse Fourier transforming the correction data 2 thus obtained, the corrected measurement result (final output) of the surface potential distribution as shown in FIG. 10 is obtained.

In the measuring apparatus 10 of the present invention, the correction function does not have to be created every time the surface potential is measured, but the distance between the object S to be measured S and the probe 24 is changed, and the probe 24 is changed. If there is, a new correction function may be created. Further, the Fourier series in the Fourier transform when creating the correction function or correcting the measurement result may be appropriately determined according to the capability of the computer that performs the Fourier transform.

The measuring device 10 described above measures the surface potential of the object to be measured S by injecting the light beam L into the optical waveguide having the electro-optical effect and examining its refraction (diffraction). However, the surface potential measuring device of the present invention is not limited to the above-mentioned aspect, and charges corresponding to the surface potential of the detected portion of the object S to be measured are applied to the optical element having the electro-optical effect, and a light beam is applied thereto. It can be used for various surface potential measuring devices as a representative of various devices that measure the surface potential by being incident and examining changes in the refractive index, phase, polarization and the like.

Specifically, the non-linear optical crystal disclosed in Japanese Unexamined Patent Publication No. 4-105072 and the non-linear optical crystal are sandwiched from both sides, and one of them is arranged to face a charged body as an object to be measured. A counter electrode provided with a bias power source for the charged body on the other side, an electrostatic shield plate having a minute aperture arranged between the charged body and one of the counter electrodes facing each other, A surface potential measuring device having a means for emitting a linearly polarized light beam to the crystal and a means for measuring the polarization of the light beam that has passed through the nonlinear optical crystal;

A crystal having an electro-optical effect disclosed in Japanese Patent Application No. 3-211988 filed by the applicant of the present invention is used as a counter electrode arranged so that one of them faces a charged body as an object to be measured. The measurement heads sandwiched between them, a light source that emits a linearly polarized light beam in the same direction as the crystal axis direction in which the temperature dependence of the refractive index change of this crystal is small, and the light beam emitted from this light source An interferometer (Mach-Zehnder interferometer) that separates the measuring light that passes through and the reference light that does not pass through, and again combines the measuring light and the reference light after the measuring light passes through the measuring head to cause interference. Light intensity measuring means (phase detection)
And a surface potential measuring device configured to include a calculating means for calculating the surface potential of the object to be measured from the measurement result obtained by the light quantity measuring means;

A charged body in which one of a light source for emitting a linearly polarized light beam and a crystal having an electro-optical effect, which is disclosed in Japanese Patent Application No. 3-225946 by the present applicant, is an object to be measured. A resonator composed of a measuring head sandwiched by opposing electrodes arranged facing each other, and two semi-transparent mirrors arranged with the reflecting surface facing the measuring head and sandwiching the measuring head in the traveling direction of the light beam. (Fabry-Perot resonator)
A means for measuring the light quantity of the light beam transmitted through the semi-transparent mirror arranged on the downstream side in the traveling direction of the light beam, and a calculating means for calculating the surface potential of the object to be measured from the obtained light quantity measurement result. Surface potential measuring device configured to have;

By the back electrode and the measurement electrode electrically insulated from each other and the ground electrode grounded, which is disclosed in Japanese Patent Application No. 3-230306 by the applicant,
A measurement head with a nonlinear optical crystal sandwiched between it and a linearly polarized measurement light and a compensation light are emitted, the measurement light corresponds to the measurement electrode of the nonlinear optical crystal, and the compensation light corresponds to the ground electrode of the nonlinear optical crystal. A light beam optical system that makes the incident light incident, a light amount measuring unit that measures the light amounts of the measurement light and the compensation light that have passed through the nonlinear optical crystal, and a calculation unit that calculates the surface potential of the DUT from the difference in the light amounts of the two. Surface potential measuring device configured to have; Non-linear optical crystal sandwiched by a back electrode, a measurement electrode electrically insulated from each other, and a ground electrode disclosed in the specification. A head and a light beam optical system that emits linearly polarized measuring light and compensating light, and makes the measuring light incident on the measuring electrode of the nonlinear optical crystal and the compensating light incident on the ground electrode of the nonlinear optical crystal. Light quantity measuring means for measuring the light quantities of the measuring light and the compensating light that have passed through the nonlinear optical crystal, a voltage applying means for applying a voltage to the back electrode so that the light quantity of the compensating light is always a constant value, and a light quantity of the measuring light A surface potential measuring device configured to have a calculating means for calculating the surface potential of the object to be measured; a non-linear optical crystal formed by a measurement electrode facing the object to be measured and a back electrode disclosed in the specification. A sandwiched measuring head, a means for short-circuiting and grounding the measuring electrode and the back electrode, and a light beam light source for emitting a linearly polarized light beam to a nonlinear optical crystal,
A light amount measuring unit that measures the light amount of the light beam that has passed through the nonlinear optical crystal, and a calculation unit that calculates the surface potential of the non-analyte from the light amount difference of the light beam when short-circuited and when not short-circuited. A surface potential measuring device; a measuring head disclosed in the same specification, which comprises a measuring electrode facing an object to be measured, and a non-linear optical crystal sandwiched by a back electrode;
A means for short-circuiting and grounding the measurement electrode and the back electrode, a light beam light source for emitting a linearly polarized light beam to the nonlinear optical crystal, and a light quantity measuring means for measuring the light quantity of the light beam passing through the nonlinear optical crystal. A voltage applying means for applying a voltage to the back electrode so that the light quantity of the light beam at the time of short circuit is always a constant value, and a calculating means for calculating the surface potential of the object to be measured from the light quantity of the light beam at the time of non-short circuit. A surface potential measuring device having the same; and the like are preferably exemplified.

Although the surface potential measuring device of the present invention has been described above, the present invention is not limited to the above-mentioned embodiments, and various improvements and changes may be made without departing from the gist of the present invention. Of course.

[0042]

As described above in detail, according to the surface potential measuring device of the present invention, the measurement of remarkably high resolution, high sensitivity and high precision is made as compared with the conventional surface potential measuring device utilizing the induced current or the like. In a surface potential measuring device using an optical element having an electro-optical effect, the resolution,
It is possible to realize good measurement of the surface potential distribution due to both sensitivity and accuracy.

[Brief description of drawings]

FIG. 1 is a view conceptually showing a side surface of an example of a surface potential measuring device of the present invention.

FIG. 2 is a diagram conceptually showing a plane of the surface potential measuring device shown in FIG.

FIG. 3 is a graph of a spreading function of the surface potential measuring device shown in FIG.

FIG. 4 is a graph of a function obtained by Fourier transforming the function shown in FIG.

FIG. 5 is an example of a surface potential distribution of an object to be measured.

6 is a diagram showing the surface potential measuring device shown in FIG.
3 is a measurement result before correction when measuring the surface potential distribution of the measured object shown in FIG.

7 is a graph of a function obtained by Fourier transforming the measurement result shown in FIG.

8 is a graph of a function obtained by multiplying the function shown in FIG. 7 by a correction function.

9 is a graph of a function obtained by filtering the function shown in FIG.

10 is an example of a corrected surface potential measurement result in the surface potential measurement device shown in FIG.

FIG. 11 is an example of a filter used in the surface potential measuring device shown in FIG.

[Explanation of symbols]

 10 Surface Potential Measuring Device 12 Substrate 14 Optical Waveguide 16 Buffer Layer 18 Lattice Electrode 20 Optical Input Linear Diffraction Grating (Input LGC) 22 Optical Output Linear Diffraction Grating (Output LGC) 24 Conductive Probe 26 Light Source 30 Measuring head 32 Photoelectric conversion element 34 Voltmeter 36 Calculation unit 38 Control unit 40 Power supply 42 Resistance L Light beam S Object to be measured

Claims (1)

[Claims] 1. An optical element having an electro-optical effect, an electrode electrically contacting the optical element and electrically proximate to an object to be measured, and a light source for emitting a light beam incident on the optical element. A measuring means for measuring the light quantity of the light beam emitted from the optical element, and Fourier transforming the surface potential distribution of the object to be measured obtained from the light quantity measured by the measuring means, and measuring the result of the Fourier transform. A surface potential measuring device, comprising: a correction unit that corrects the spread function of a measurement region included in the system and then performs an inverse Fourier transform on the spread function to obtain a measurement result of the surface potential distribution.