JP4950084B2 - Method for predicting abnormal image of photoconductor - Google Patents

Description

  The present invention relates to a method for predicting the breakdown of a latent image on an electrophotographic photoreceptor, and thus the breakdown of an image.

First, a description will be given of a technique for measuring a latent image in a minute area according to the present invention.
An electrophotographic method used in a copying machine or a laser printer includes a step of uniformly charging the surface of a photoconductor, and a step of exposing the charged surface of the photoconductor to form an electrostatic latent image on the surface of the photoconductor. Developing the electrostatic latent image with toner in the developer, transferring the toner image to paper or an intermediate transfer belt, fixing the transferred toner image, and on the photoreceptor after transfer It consists of a cleaning process for removing residual toner and a charge eliminating process for removing the electrostatic latent image on the photoreceptor.

  Since each process has an effect on the output quality of the final image, it is not easy to know the latent image quality in the exposure process from the final image. Estimate the quality of the latent image formed by measuring the post-potential and seeing how these characteristic values change in a temperature and humidity environment or after repeated charging and exposure cycles. I had to do it. However, in this method, evaluation of abnormal images such as background contamination, image blur (or image blur), which is degradation of the latent image, which is a deterioration of the latent image, is based on the fact that the surface electrometer measures a wide area on the photoconductor (photoconductor surface). Since the charging potential in the region of 10 to 15 mmφ with respect to the distance of 2 mm between the surface electrometer probe and the surface electrometer probe was measured macroscopically, it was impossible to know the abnormality of the latent image.

In the trend toward higher image quality, there is a need for a method of directly measuring an electrostatic latent image in a minute area and evaluating the state of the latent image. For this reason, several methods for directly evaluating an electrostatic latent image in a minute area have been proposed recently.
For example, (1) Cantilever method: mechanical displacement of a cantilever beam caused by a force F (electrostatic attractive force, etc.) acting between the photoreceptor surface and the probe, or a change in vibration state is applied to the back surface of the cantilever beam. A method of irradiating a laser beam, detecting the reflected light, and knowing the surface potential from the value of the amount of displacement (see Patent Document 1: Japanese Patent Laid-Open No. 5-119093, Patent Document 2: Japanese Patent Laid-Open No. 5-149988) ), (2) Electrometer method: a method in which an electrode having a certain area is disposed in the vicinity of the surface of the photosensitive member, and the electric potential induced in the electrode has a potential with respect to the ground (Patent Document 3: Japanese Patent Laid-Open 11-184188, Patent Document 4: JP-A-11-184189, Non-Patent Document 1: W. Hillen et al, SPIE Vol. 914 Medical Imaging II (1988) p253, Non-Patent Document 2: Enrique Garcia et al. , IEEE Transaction Devices 38 (5) (1991) p1077), (3) Displacement current method by light attenuation (inductive current method): An electrode placed close to the surface of the photoconductor, irradiating a charged surface of the photoconductor with a very small light spot, Method of measuring the amount of electric charge (induced current) induced in the electrode and knowing the surface potential (Non-patent Document 3: Takeshima Motoharu et al., Japan Hardcopy 2001 Proceedings, B-32, 281 pages, Non-Patent Document 4: JARowlands et al, Med. Phys. 18 (3), May / Jun 1991, p421).

  In the method (1), the cantilever and the photosensitive member come into contact with each other with an electrostatic force at a charging potential of several hundred volts as in the photosensitive member. Further, if the distance is set so as not to contact, the spatial resolution is lowered, and there is a problem that sensitivity deterioration cannot be avoided if a material having a bending force that does not contact the distance as it is is used for the cantilever beam.

In the method (2), it is necessary to induce an amount of charge corresponding to the amount of charge in a predetermined region on the surface of the photoreceptor on the electrode, and it is necessary to narrow the gap between the photoreceptor and the electrode. In general, in this method, when A (μm) is required as the spatial resolution of measurement, the gap must be within A (μm), and the electrode size must be within A (μm) × A (μm). (See Non-Patent Document 2). Therefore, in order to realize a spatial resolution of 10 μm, it is necessary to make a gap of 10 μm or less with a small electrode of 10 × 10 μm ² or less. In this method, since the charged photoconductor moves and the displacement current induced when the charge on the surface of the photoconductor crosses the electrode is measured, it is necessary to always maintain this minimum gap. Is extremely difficult. In Patent Document 3 and Patent Document 4 adopting this method, there is a description that means for keeping the distance between the surface of the photoreceptor and the detection portion of the potential sensor constant is provided. To provide a mechanism to maintain a constant interval mechanically, or to monitor the interval using a laser gap sensor or an eddy current displacement sensor and control with a motor or the like to always maintain a constant interval Are listed. However, if the spacer is sandwiched between the gap between the surface of the photoreceptor and the electrode, it is obvious that the surface is scratched with the movement of the photoreceptor surface, which is not preferable. In addition, the eddy current method for monitoring distance has a problem of responsiveness of distance measurement, and the laser method absorbs light by the photoconductor and the reflected light becomes small and an error is likely to occur. It can be said that it is not preferable to use the photoconductor as a counterpart because it causes unnecessary photodegradation. In Non-Patent Document 1, 32 microelectrometers (electrodes) each having a size of 0.2 × 0.2 mm ² are arranged in the drum axis direction at a pitch of 12 mm, and the average gap with the photoconductor is 0.1 mm ± 0. .02mm is realized. The error is assumed to be due to the placement error of each electrode and the rotational deviation of the photosensitive drum, and there is no description of a specific mechanism for maintaining the gap with high accuracy. Non-patent document 2 uses a CCD array (5 × 5 μm ² ) as an electrode. However, it is described that the target of a gap of 5 μm can be controlled and maintained only to about 20 μm by using a bearing of a pneumatic bearing. Yes. Details about the mechanism are unknown. In any case, the electrode must be made small for spatial resolution, the signal obtained is small because it is small, and a mechanism for maintaining a minimum gap on the order of μm is prepared. Measurement is difficult and measurement is not easy.

  In the method (3), an electrode in which a transparent conductive film is formed on transparent glass is used, and light irradiation is performed from the back side. In principle, the spatial resolution depends only on the size of the spot light to be irradiated. The electrode size is arbitrary. The distance (gap) between the surface of the photoconductor and the probe is also arbitrary up to about 2 mm (however, as a matter of course, the detection signal decreases as the gap increases). By the way, according to Non-Patent Document 3, a 10 μm-sized beam spot is irradiated from the back surface of the transparent glass electrode, an induced current (displacement current) due to a change in optical attenuation potential generated in the 10 μm region is detected, and the magnitude of the signal From this, the potential before spot light irradiation is known, and the measurement position is sequentially changed to obtain a latent image profile (one-dimensional profile in the sub-scanning direction), but one line of latent image is obtained with a beam of 80 μm width (sub-scanning direction). The latent image width at the time of writing is measured to be a width (μm) which is about twice as large as 80 μm width, and this is a method that is technically excellent, but this method is also a method for which further improvement is desired.

  Non-Patent Document 4 also relates to the method of (3), and mentions the principle of measurement using the light attenuation characteristics of the photosensitive member. However, the X-ray fluoroscopic image of the human body is not a silver halide film. Instead, it describes a technical problem related to X-rays of a device that projects onto a charged inorganic photosensitive member (Se) and reads a two-dimensional electrostatic latent image formed on the surface of the photosensitive member as electronic data to a computer.

  Non-Patent Document 5 (DSWeiss, et al. “Analysis of Electrostatic Latent Image Blurring Caused by Photoreceptor Surface Treatments” J of IS & T 40, No. 4, 1996) is a model model of diffusion with the photoreceptor surface resistance as a parameter. Is described with respect to time. Although closely related to the present invention, there is no mention of predicting image distortion without combining the actual measurement data of the latent image and the model formula and without generating an image. Also, in order to see the change in image width after repeated use due to the presence or absence of an overcoat layer, exposure is performed from an analog voltage signal when xenon lamp light (non-Gaussian distribution) is exposed from a wide slit of 0.25 cm width through a monochrome filter. It is a macro that looks at the boundary between the area and the non-exposure area, and it is difficult to say that it is well suited for measuring a latent image in a minute area.

In addition to this, there are those related to measuring a latent image of a minute region using an electron beam (Patent Documents 5 to 8).
Patent Document 5: Japanese Patent Laid-Open No. 2006-84434 describes that the insulation resistance is evaluated with an accuracy of the order of μm, and Patent Document 6: Japanese Patent Laid-Open No. 2006-10430 includes a detection means. Patent Document 7: Japanese Patent Application Laid-Open No. 2005-166542 discloses that surface potential distribution is measured with extremely high accuracy without using secondary electrons. Patent Document 8: Japanese Patent Application Laid-Open No. 2004-251800 describes a method for accurately measuring the surface charge distribution by setting the irradiation current of the charged particle beam to a size that does not cause the surface charge distribution to disappear. ing.
However, when the sample is measured in a vacuum, and it is desired to evaluate the electrostatic latent image created on the deteriorated sample, the surface has something to be attached by taking time and taking the vacuum. If so, it is possible that it will be removed and the degradation state will change. Therefore, the present invention differs from the present invention in configuration, technical problem, and purpose. Patent Document 9 is a publication of an already-invented invention related to the present inventor, and the present invention corresponds to the improved application invention of Patent Document 9.
Patent Document 9: Japanese Patent Laid-Open No. 2006-38666 describes that in the measurement of displacement current due to a change in optical attenuation potential, the S / N ratio of the detection signal is improved while ensuring the spatial resolution in the sub-scanning direction. .

Japanese Patent Application Laid-Open No. 5-119093 Japanese Patent Laid-Open No. 5-149988 JP-A-11-184188 JP-A-11-184189 JP 2006-84434 A JP 2006-10430 A JP 2005-166542 A JP 2004-251800 A JP 2006-38666 A W. Hillen `` A selenium-based detector system for digital slot-radiograph '' SPIE Vol.914 Medical ImagingII, P253,1988 Enrique Garcia “CCD Arrays for Readout of Electrophotographic Latent Images” IEEE TRANSACTIONS ON ELECTRON DEVICES 38, NO.5, P1077, 1991 Takeshima, Aizawa "1DOT Latent Image Potential" Japan Hardcopy 2001 Proceedings p281 J. A Rowlands et al. `` X-ray imaging using amorphous selenium: A photoinduded discharge readout method for digital mammography '' Med.phys 18 (3), 1991 D.S.Weiss, et al. `` Analysis of Electrostatic Latent Image Blurring Caused by Photoreceptor Surface Treatments '' J of IS & T 40, No. 4, 1996

The present inventors have already proposed (Japanese Patent Application No. 2007-184847) an application technique of the method belonging to the prior art (3). Since this method is measurement in the atmosphere, the initial state of the photoreceptor and the deterioration state due to the load are not impaired, and the electrostatic latent image on the photoreceptor is directly evaluated to know the resistance of the photoreceptor to the load. Specifically, a latent image measuring device is provided, and specifically, a charger, an exposure device (1) (latent image writing means), a transparent conductive electrode, and a back surface thereof are arranged around a cylindrical photosensitive member. The exposure device (2) (detection light exposure means) and the static eliminator are arranged in this order, and the exposure device (1) forms a latent image pattern on the surface of the photosensitive member, and the pattern is a transparent conductive electrode portion. , The rotational movement of the photosensitive member is stopped, one-shot pulse exposure is performed by the exposure device (2), and a signal induced in the transparent conductive electrode is collected along with the light attenuation of the charge on the photosensitive member. Step the photoconductor over the beam width (thickness) in the circumferential direction of the exposure device (2). In a measuring apparatus that moves and repeats signal sampling in the same manner, the exposure unit is such that the latent image pattern formed by the exposure unit (1) is a line pattern of at least 2 lines / mm or more in the photosensitive member rotation direction. The present invention relates to a minute area latent image measuring device whose content is to control (1). However, it has been found that when the latent image measuring device measures the “displacement” of the latent image, the image forming device may not recognize the “displacement” of the image when the image is output by the image forming apparatus. . That is, there are cases where the result of the micro area latent image measurement and the result of image output do not correspond. As a result of pursuing the cause, in the latent image measurement, a latent image pattern was formed on the charged photosensitive member by exposure, and it took more than 1 second until the pattern reached the transparent electrode portion and the measurement was started. In addition, in the image forming apparatus, it was found that the time from exposure writing to development is around 0.1 seconds, and this point is different. This suggests that when the surface resistance of the photosensitive member is deteriorated by a load, there is a great difference in how the latent image is broken at a certain resistance level after 0.1 seconds from the formation of the latent image and after 1 second or more. However, it is difficult for the inventors to measure the latent image of a minute area from the latent image formation to the start of measurement in about 0.1 seconds due to the limitations of the measuring apparatus. However, it is difficult to output the image after 1 second or more after the latent image is formed, and it is difficult to match the result of the latent image measurement of the deteriorated photoconductor and the image output result at the same time. there were. This means that it is difficult to directly confirm the influence of time on the latent image.
In view of the above, the present invention combines a latent image measurement result on a photoconductor and a numerical calculation result of a model formula relating to a latent image potential, and can accurately predict an image output result in an image forming apparatus when the photoconductor is used. Is to provide a method.
[Purpose 1]
Means for measuring the shape of the electrostatic latent image as an electric potential with respect to the electrostatic latent image formed on the surface of the photosensitive member, and the surface resistance of the surface of the photosensitive member as the movement of the electric charge in the electrostatic latent image In a method for specifying the surface resistance of the photoconductor by combining with a means for calculating by numerical calculation of a model formula using elapsed time as a parameter, the time required from the exposure writing to the start of measurement in the measurement is written in the numerical calculation. The surface resistance value of the photosensitive member is determined from the measurement result of the latent image shape and the numerical calculation result of the latent image shape using the surface resistance of the photosensitive member as a parameter. An object of the present invention is to accurately predict image distortion in an image forming apparatus by using the time from exposure to development of an image forming apparatus on which a body is mounted and calculating the shape of a latent image under the conditions. To do.
[Purpose 2]
When the means for measuring the shape of the latent image is a means that can evaluate the resolution of 1 line / mm or more in the atmosphere, even if the surface of the photoconductor is deteriorated by a load, the state is impaired. Since the measurement resolution is 1 line / mm or more, the shape of the latent image has high measurement accuracy, and the correspondence with the numerical calculation result can be determined with high reliability. .
[Purpose 3]
The means for measuring the shape of the latent image is a measuring method using the light attenuation function of a photoconductor, thereby providing means for specifically achieving the object 2.

The above-mentioned subject is achieved by the present invention as follows.
(1) “Measuring means for measuring the shape of the electrostatic latent image as a potential with respect to the electrostatic latent image formed on the surface of the photosensitive member; Is a method for specifying the surface resistance of the photosensitive member by combining with a means for calculating the surface resistance and elapsed time of the model equation as parameters, and is required from the exposure writing in the measurement to the start of the measurement. The time is used as the elapsed time from writing in the numerical calculation, and the photosensitive member surface resistance value is determined from the measurement result of the latent image shape and the numerical calculation result of the latent image shape using the photosensitive member surface resistance as a parameter. Using the surface resistance value and the time from exposure to development of the image forming apparatus on which the photoconductor is mounted, the shape of the latent image under the conditions is calculated, and the image distortion of the photoconductor in the image forming apparatus is calculated. How to predict ",
(2) “The means for measuring the shape of the latent image is a means capable of evaluating a resolution of 1 line / mm or more in the atmosphere”. How to predict breakup ",
(3) “Method for predicting image distortion according to item (1), wherein the means for measuring the shape of the latent image is a measurement method using a light attenuation function of a photoconductor” .

According to the first aspect of the present invention, it is possible to accurately predict the image distortion in the image forming apparatus from the combination of the latent image measurement result and the numerical calculation result based on the charge diffusion model formula.
Further, according to claims 2 and 3, the accuracy of the latent image measurement is improved, and the object of claim 1 is easily achieved.

  In the present invention, a charged photosensitive member is exposed to form a rectangular latent image pattern in a minute area within a width of 1 mm, and the latent image is subjected to one-shot exposure with a line beam laser to change the surface potential due to light attenuation. Measure the change in the amount of charge induced by the electrode placed close to the photoreceptor due to the change in potential, that is, the induced current (displacement current), and measure the level of the surface potential before exposure from the magnitude of the signal. The charge on the photoconductor, that is, the latent image potential as a substitute characteristic, is based on the results of measuring the shape of this latent image potential and the model of the latent image potential. This is a method for accurately predicting the state of an image when an image forming apparatus outputs an image by combining numerical movement results of movement.

  Until now, a measuring instrument for measuring the surface potential of a photosensitive member has been used in a system called a vibration capacity type. A commercial product of this surface potential measuring instrument is Trek Model 344. The gap between the photoconductor and the surface electrometer probe is usually 1 mm to 3 mm in many cases. At this time, the area detected by the probe of the surface electrometer is 5 mmφ to 20 mmφ, and the gap is 0.5 mm. However, the detection area is 2 mmφ, and it is impossible to measure the latent image with high accuracy from the viewpoint of spatial resolution. Therefore, various techniques described above have been studied, but there are problems that are difficult to put into practical use, and diligent development efforts continue. In the present invention, since the latent image measurement is based on a method using light attenuation of the photosensitive member, the latent image potential in a region of 1 mm width or less on the photosensitive member is accurately evaluated from the viewpoint of spatial resolution. In addition, when the surface of the photoconductor is contaminated with corona discharge products due to corona charging and the surface resistance is deteriorated, measurement in the atmosphere is possible, and it takes a lot of time to prepare for the measurement. Therefore, the latent image formation state under the condition can be measured without impairing the deterioration state.

Next, as a writing pattern in latent image measurement, it has been found that forming two or more V-shaped potential patterns in a width of 1 mm makes it easy to discriminate the latent image potential. Yes. However, in the present invention, in order to determine whether the image output is lost when the measurement result of the latent image potential on the photosensitive member is broken, numerical calculation of the diffusion and movement of the latent image potential is performed based on the model formula. become. Although the model formula will be described later, the starting point of the model formula is a partial differential equation, and in order to solve this easily, the latent image potential pattern is preferably a rectangular pattern (= well type potential). Therefore, the writing pattern in the latent image measurement is also a rectangular pattern.
The method of exposing a rectangular pattern to a charged photoreceptor moving (rotating) at a linear velocity v is as follows:
(I) When a rectangular pattern having a width A is exposed for a very short time, for example, when A is 0.5 mm wide and the photosensitive member linear velocity v is 50 mm / s, the formed width A has an error of 1% or less. The exposure is performed at least at 0.5 × 0.01 ÷ 50 = 0.0001 s (= 100 μs) or less. In this case, the exposure pattern is required to have as uniform illuminance within the width A as possible.
In another method, (ii) a pattern having an exposure width of 1/10 or less of the width A is irradiated for a time of A ÷ v = 0.5 / 50 = 0.01 s. In order for the latent image to be formed to have a rectangular width A, it is preferable that the exposure width pattern be as narrow as possible and that the illuminance be uniform within that width.
In the micro area measurement used in the present invention, a linear beam is used in the method (ii), and its width (thickness) is 45 μm. In addition, the illuminance distribution in the width direction is a Gaussian distribution, and there is an influence of the tail cut, and ideal exposure is not achieved. However, the method (i) is also extremely difficult to expose with a uniform illuminance distribution.

  Here, a model equation for the movement / diffusion of electrostatic charges on the surface of the photoreceptor, and hence the movement / diffusion of the latent image potential, will be described. If the potential is V, it is expressed by the following partial differential equation in one dimension as a function of position and time.

ここに、Ｄは拡散係数

Where D is the diffusion coefficient

（Ｒ_ｓｑは表面抵抗、Ｃは単位面積当たりの静電容量である。）
矩形の潜像電位パターン（＝井戸型ポテンシャル）は、その中央をｘ＝０、幅を２ａとすると、
初期条件はｔ＝０のとき、ｘ＝０ではＶ＝Ｖ_ｅｘｐ（露光直後の電位）、
ｘ＝ａ ｏｒ −ａではＶ＝Ｖ_０（初期帯電電位）となり、これを解いて（２）式が得られる。

(R _sq is the surface resistance, and C is the capacitance per unit area.)
A rectangular latent image potential pattern (= well-type potential) has a center of x = 0 and a width of 2a.
The initial conditions are t = 0, V = V _exp (potential immediately after exposure) when x = 0,
When x = a or −a, V = V ₀ (initial charging potential) is obtained, and the equation (2) is obtained by solving this.

ここに、ΔＶ_０＝Ｖ_０−Ｖ_ｅｘｐ、
Erf は「誤差関数」であり、次式（３）のように表わされる。

Where ΔV ₀ = V ₀ −V _exp ,
Erf is an “error function” and is expressed as the following equation (3).

（*）は非特許文献５より引用

(*) Is cited from Non-Patent Document 5.

As can be seen from the equation (2), V is a function having the surface resistance (R _sq ) and the capacitance (C) as parameters.
The results of numerical calculation using this equation under the following conditions are shown in FIGS. 7-1, 7-2, 7-3, and 7-4.
a = 200 μm (width: 400 μm)
V ₀ = 800V
ΔV ₀ = 400V
Time after exposure: 0.1 s, 1 s, 10 s
Surface resistance: 1 × 10 ¹⁶ Ω / □, 1 × 10 ¹⁵ Ω / □, 1 × 10 ¹⁴ Ω / □, 3 × 10 ¹³ Ω / □
Capacitance: 100 pF / cm ²
The calculation was performed using spreadsheet software (Microsoft Corporation, Excel2000).
The reason why the data of 0.1 s is not plotted when the surface resistance is 1 × 10 ¹⁶ Ω / □ is that the calculation cannot be performed.

From the numerical calculation, it can be seen that when the surface resistance of the photosensitive member is about 3 × 10 ¹³ Ω / □, there is a large difference in the latent image pattern after exposure 0.1 s and after 1 s. Since the latent image is broken from the data after 1 s, it is easily imagined that the image output is also broken, but if the image forming apparatus is developed after 0.1 s from the exposure, the image It can be read from the data of 0.1 s that the deformation is almost unnoticeable. That is, it can be seen that it is not possible to determine what kind of result is obtained with respect to the state of the image only from the measurement result of the latent image. In order to predict the output result of an image without displaying the image, it is necessary to consider diffusion depending on the latent image time.

  Therefore, the shape of the rectangular electrostatic latent image on the surface of the deteriorated photoconductor is measured, and the surface resistance of the equation (2) is changed variously in the time required for this measurement, so that the shape (displacement) of the latent image is roughly determined. The matching surface resistance value is defined as the surface resistance of the photoconductor, and then the surface resistance value and the time from exposure to development in the image forming apparatus on which the photoconductor is to be mounted are used to calculate the latent image from equation (2). It is effective to calculate the potential and predict whether the image output will be lost from the shape of the latent image potential.

  So far, it has been explained that the agreement between the measurement result of the electrostatic latent image and the result of numerical calculation with various surface resistances is judged in the form of the latent image, but the judgment criterion is not limited to this, and the rectangular potential is not limited to this. It is preferable to judge in consideration of specific values such as the potential before exposure of the pattern, the potential (minimum value) level after exposure, the exposure width, and the like. This will be described later.

  A commercially available surface electrometer may be used for latent image measurement, but this is not preferable in terms of performance of spatial resolution. For the purpose of predicting whether or not an image will be lost without outputting the image of a deteriorated photoconductor, the image loss may be “weight”, “blur”, or “flow” at the edge of the image. These are abnormalities expressed by the above, and these are phenomena that appear within a width of 1 mm. Therefore, the latent image measurement is preferably performed with a measuring instrument having a spatial resolution capable of measuring a latent image within a width of 1 mm.

The latent image measurement used in the present invention will be described.
In the latent image measuring device, the exposure unit used for forming the latent image pattern can be realized by an imaging optical system, a beam scanning type writing optical system, or the like. However, in the method used in the present invention, the line pattern needs to have a width of 1 mm in the rotation direction of the photosensitive member and a length (20 mm) or more of the detection light (line beam) in the axial direction of the photosensitive member. Although exposure with uniform illuminance is required in the direction, it is difficult to realize the optical system design because it requires some ingenuity. In addition, although exposure with a constant illuminance in the axial direction is easy with a beam scanning type exposure device, the polygon of the polygon is determined from the linear velocity of the photosensitive member, the resolution in the sub-scanning direction of writing (dpi), the number of mirror surfaces of the polygon, and the like. It is necessary to determine the number of rotations (rpm) and set the timing of the exposure start beam in the main scanning direction, and it is necessary to set the beam intensity for each line in the main scanning direction. Incorporation into a measuring device is difficult to use, for example, it is necessary to carry out with the same accuracy as the control of the writing optical system. For this reason, it is preferable that a line beam laser is separately prepared and used as the exposure device used for forming the latent image pattern, similarly to the exposure device used as the detection light. In this case, a length is already secured in the photosensitive member axial direction (main scanning direction), and in the rotating direction (sub-scanning direction), the exposure width of the exposure unit is adjusted to 1 mm in accordance with the photosensitive member linear velocity. By determining the lighting time and controlling the optical power within this time, a latent image pattern is easily formed.

  This is the reason for using a line beam for the detection light in the measurement device. In the conventional technology using light attenuation, the measurement position is changed in a minute step in the direction of rotation of the photoconductor, and the beam spot is exposed. . The measurement is repeated at different positions, and finally a one-dimensional profile of the latent image is obtained. However, in order to secure the spatial resolution of the measurement, it is necessary to reduce the beam used for potential detection. There is a problem in that the area where the occurrence of noise occurs is small, the signal obtained is small, and measurement is impossible. Possible solutions to this problem include (1) improvement of the signal processing circuit (amplifier circuit), (2) improvement of the S / N ratio by bringing the electrode closer to the photoconductor. In (1), there is known a means for repeatedly capturing the same signal with respect to a minute signal and superimposing it to ensure an S / N ratio, but it can be applied to a one-shot signal (meaning a single signal). However, this method is difficult due to the principle of measurement. The method (2) is effective, but even if the electrode-photoreceptor distance of 1 mm is 0.5 mm, it is only about twice as high, and the effect is small when the signal is buried in noise. Since the measurement method measures a one-dimensional profile of the latent image in the photoconductor rotation direction (sub-scanning direction), the detection light exposure size in the axial direction (main scanning direction) of the photoconductor is increased, that is, the potential changes. By enlarging the region where this occurs, the spatial resolution in the sub-scanning direction is ensured (the resolution in the main scanning direction is ignored), and the S / N ratio of the signal is improved.

  All measurements were performed with the apparatus configuration shown in FIG. The conductive electrode member is preferably formed by forming a transparent conductive thin film on transparent glass, which can be irradiated with light through the electrode when the glass electrode is opposed to the photoreceptor sample. Ease of use improves. The transparent glass may be general glass, but BK-7, quartz glass, and the like have a wide pass wavelength range and are preferable for measurement. In addition, ITO is generally used as the transparent conductive thin film, but there is no problem with other than this. The transparent conductive film can be formed on the entire surface of one side of the glass or in a mesh shape with a fine line (≦ 1 mm) using a pattern mask. Moreover, when the light to pass is a laser, it is preferable to attach an antireflection film to the glass on the laser incident side. This is to prevent so-called return light noise, in which the laser beam reflected from the glass surface on the laser incident side returns to the light emitting portion, forms a composite resonator, and the laser beam fluctuates. When this transparent electrode is placed opposite to the sample, the closer the distance to the sample, the greater the signal, which is preferable. However, the reflected light from the surface of the photoreceptor is reflected on the glass electrode surface and is expected to enter again. It is desirable to provide an antireflection film on the surface facing the photoconductor. The effect of reducing the spread of light can be expected.

More specific description will be given below.
<Configuration of latent image measuring device>
The measuring apparatus has the configuration shown in FIG. 2, and operates by rotating the photosensitive drum, charging (using a scorotron charger), and writing using the exposure device (1) (exposure time = target writing width / photosensitive linear velocity). When the formed latent image arrives at the electrode part, the charging / rotation is stopped, and the exposure device (2) (line beam laser (main scanning direction) 20 mm × (sub-scanning direction) 24 μm−655 nm−) is irradiated as detection light. To do. When the induced current (displacement current) due to potential decay is measured, the photosensitive drum is rotated and moved (50 μm) to the next measurement position, and the next detection light is irradiated to measure the induced current (displacement current). This measurement is repeated until the entire latent image width is measured (FIGS. 2 and 3). The relationship between the charging potential and the magnitude of the induced current (displacement current) is investigated in advance, and the charging potential at that time is determined from the measured magnitude of the induced current (displacement current). This is used as the latent image width. By plotting against this, the one-dimensional profile of the latent image can be known.

<Example 1>
The experimental apparatus shown in FIG.
・ Charger: High voltage power supply for mains Trek 610C
Power supply for grid bias Matsusada Precision Co., Ltd. HJPM-1.5
・ Surface potential meter: Trek Model 344
Exposure unit (1): Global Laser Lyte-MV laser line generator module, radiation angle 30 °, wavelength 635 nm,
Focal length Adjust the optical system in the module so that it is 83mm from the laser output end of the module. Exposure power control Linear modulation DC0 ~ 1V (at DC ~ 200kHz)
The output optical power is attenuated by the neutral density filter 1/125, and then 0 to 0.5 VDC
It lights in the range of (see FIG. 15).
Exposure time control (Latent image pattern width to be formed / Photoconductor linear velocity) + Adjust exposure time, Exposure power
Is controlled by an arbitrary waveform generator (Agilent Technology HP33220A)
According to the installation position Installed at an angle of 45 ° to the horizontal

Exposure unit (2): Ricoh Optical Co., Ltd. line beam laser wavelength 655 nm
Line thickness 24μm
Line length 20mm
Focal length Distance between laser emitting end and photoconductor 74 mm-unique value of this exposure device (fixed)
Exposure energy Set by laser power x laser lighting time. Laser power is LD drive power
By flow. Here, the surface potential of 800 (-V) is attenuated to 100 (-V) as defined above.
“Necessary exposure energy” is exposed and the laser lighting time is 2 μs.
The laser power was set according to the sensitivity characteristics of the photoreceptor. All this
Exposure is performed under the following conditions.
・ Transparent conductive electrode: Substrate:
Quartz glass 10mm × 30mm × 1mmt
Surface facing the photoconductor Conductive electrode with antireflection film:
ITO (102.8) / SiO ₂ (103.15)
Back side (laser incident side) antireflection film:
Ta ₂ O ₅ (25.49) / SiO ₂ (38.15) / Ta ₂ O ₅ (86.74) / SiO ₂ (111.65)
Figures in parentheses are film thickness units in nm
All gaps with the photoreceptor were 0.1 mm.
・ Exposure device (2) trigger: Arbitrary waveform generator (Agilent Technologies HP33120A)
One shot pulse was generated and used as a trigger.
The generated pulse width was 2 μs.
Mounting position Horizontal position / Signal processing system: Current amplifier (KEITHLEY 428) + Oscilloscope (Yokogawa DL708)
-Controller: PC (self-made software), control of measurement device, data processing-Drum rotation device: Suruga Seiki Co., Ltd. precision rotation stage KS432-75
Driver D220
Resolution 0.0025 ° / pulse
Positioning accuracy 0.03 °
The rotation speed was set to 50 ° / s.
Photosensitive drum: A laminated OPC (organic optical semiconductor) drum manufactured by our company 60 mmφ × 334 mm long, and the exposure energy required for the potential attenuation from 800 (−V) to 100 (−V) is approximately 0.3 μJ at 655 nm. / Cm ² around.

Use this device,
(1): First, calibration curve data was measured for the photosensitive drum (unused product) to be measured.
The scorotron grid bias of the charger and the high voltage applied to the wire were sequentially changed. When the charging unit reached the electrode unit, the rotation was stopped and the detection light was irradiated. The detection light was irradiated six times, the first two data were discarded, and the average value of the remaining four data was used as the signal intensity obtained at the charged potential. The target charging potential is as follows. An example of the measured signal data is shown in FIG. 4, and an example of the obtained calibration curve data is shown in FIG. The measurement was performed at the timing shown in FIG. 3 with the exposure device (1) “latent image writing” disabled.
The following is the target charging potential.
900 (-V), 800 (-V), 700 (-V), 600 (-V), 500 (-V), 400 (-V), 300 (-V), 200 (-V), 100 ( -V)

(2): FIG. 6A and FIG. 6B show voltage data for controlling the optical power of the exposure device (1). In FIG. 6A, the horizontal axis is the time axis. In FIG. 6B, this is converted into data on the surface of the photosensitive member using the photosensitive member linear velocity data. The exposure time was about 3.75 ms, and the control width on the exposure surface was 98 μm. In this case, since a rectangular exposure width is formed by a linear beam having a thickness of 45 μm (= width), the beam exposure control width is made smaller than the target exposure width of 300 μm in consideration of the influence of the thickness of the linear beam, the tail cut and the like.
Charging is started, and when the head of the charging unit is rotated by 270 °, the exposure device (1) is controlled by the data shown in FIG. When the exposure start position reaches the horizontal position where the electrode is located, the rotation is stopped, and exposure is performed from the back surface of the transparent electrode by the exposure device (2) in 2 μs, and the current induced in the transparent electrode is detected. The time from exposure to measurement start was 5 s. The signal that has passed through the current amplifier is acquired by a digital oscilloscope. The measurement position was moved in 50 μm steps (0.0955 ° rotation for a 60φ drum), and the measurement was repeated. The exposure device (2) was exposed 21 times. The first two batches were discarded, and the 19 measurement data were applied to the calibration curve data shown in FIG. 5 to read the corresponding surface potential. The results are shown in FIG. The width of the rectangular pattern of the latent image was aimed at 300 μm. In FIG. 8, it is measured at about 300 μm. Since the measurement position is changed in steps of 50 μm, it can be said that it is almost accurate if measured in the range of 300 μm ± 50 μm. However, the power of a 45 μm thick (= width) linear line (see FIG. 15) is changed to expose a rectangular pattern, and the formed latent image is not a complete rectangle. Therefore, when comparing the measured result with the shape of the latent image of the numerical calculation based on the model formula, in addition to the overall shape, the exposure width, the potential before exposure, the level of the potential after exposure, etc. are taken into consideration. .
Note that the reason for discarding the first two data during calibration curve data measurement and latent image pattern data measurement is that the circumferential size of the line beam of the exposure unit (2) is 24 μm, but the tail is completely cut off. This is because it affects 100 μm ahead.

In the experimental apparatus used, the rotation speed was set to 50 ° / s, and it was known at the preparation stage of the experiment that an average of 1.5 s was required from the writing of the rectangular latent image pattern to the start of measurement. This time is a constraint condition of this experimental apparatus. In this experimental apparatus, the measurement control software can specify the waiting time until the measurement is started, and the measurement result is obtained by setting the waiting time from writing to the measurement to be 5 s.
Next, in order to match this measurement result, in the formula (2), time t = 5 s and the value of the surface resistance R _sq was changed to perform numerical calculation. FIG. 9 shows the result of numerical calculation using this equation under the following conditions.
a = 150 μm (width 2a = 300 μm)
V ₀ = 800V
ΔV ₀ = 400V
As shown in FIG. 9, it was determined that the surface resistance close to the measurement result of FIG. 8 was 2 × 10 ¹⁶ Ω / □.

  Next, using this surface resistance value and the time of 0.11 s from exposure to development of the prepared image forming apparatus, equation (2) was calculated, but calculation was not possible, so calculation was made using time 1 s. The results are shown instead (see FIG. 10). The result which is not largely different from the calculation result of 5s was obtained. It can be seen that the shape of the latent image does not vary greatly after 1 s from writing, and therefore after 0.11 s and after 5 s, and the image does not break with this surface resistance.

<Example 2> Including Comparative Example A photoconductor obtained by repeating image formation about 10,000 times with an image forming apparatus was placed in an ozone bac tester (concentration: 5 ppm), and bacterized for 5 days. The latent image measurement of this photoconductor was performed in the same manner as in Example 1. However, the time from writing to the start of measurement was 2 s. The result before ozone bakuro and the result after bakuro are shown in FIG. 11 and FIG.
Next, numerical values were calculated by changing the value of the surface resistance R _sq with the time t = 2 in the equation (2) so as to coincide with the measurement result (FIG. 12). As shown in FIG. 13, the surface resistance close to FIG. 12 was a surface resistance of 1 × 10 ¹⁴ Ω / □.
Next, using this surface resistance value and a time from exposure to development of the prepared image forming apparatus of 0.11 s, the calculation shown in FIG. 14 yielded the result shown in FIG. The result was significantly different from the calculation result of 2s, and it was expected that a normal image was obtained. From the latent image measurement result (FIG. 12), it was determined that a normal image could not be obtained, but when the image was output by the image forming apparatus, there was no problem (see FIGS. 16-1 and 16-2). This coincided with the prediction of the calculation result (FIG. 14) using the time from exposure to development of the image forming apparatus of 0.11 s.
It can be seen that the image output result can be accurately predicted by combining the latent image measurement and the numerical calculation based on the model formula.

It is a figure which shows the flow of the measuring method in this invention. It is a block diagram of the micro area | region latent image measuring device used by this invention. It is a figure explaining the timing of the latent image measuring device used by this invention. It is a figure which shows the example of the signal obtained with the latent-image measuring apparatus used by this invention. It is a figure which shows the example of the calibration curve data used with the latent image measuring apparatus used by this invention. It is a figure which shows the example of the optical power control voltage of the line beam for latent image pattern formation of the latent image measuring device used by this invention. (The horizontal axis is the time axis.) It is a figure which shows the example of the optical power control voltage of the line beam for latent image pattern formation of the latent image measuring device used by this invention. (The horizontal axis is replaced with the “position” on the photoconductor.) It is a figure which shows the calculation result of the latent image electric potential obtained by the model type | formula in this invention. Photoreceptor surface resistance 1 × 10 ¹⁶ Ω / □ It is a figure which shows the calculation result of the latent image electric potential obtained by the model type | formula in this invention. Photoreceptor surface resistance 1 × 10 ¹⁵ Ω / □ It is a figure which shows the calculation result of the latent image electric potential obtained by the model type | formula in this invention. Photoreceptor surface resistance 1 × 10 ¹⁴ Ω / □ It is a figure which shows the calculation result of the latent image electric potential obtained by the model type | formula in this invention. Photoreceptor surface resistance 3 × 10 ¹³ Ω / □ It is a figure which shows the shape of the latent image obtained with the latent image measuring apparatus used by this invention. Measurement data after 5 seconds from exposure to start of measurement. It is a figure which shows the calculation result of the latent image electric potential obtained by the model type | formula in this invention. Calculation results after 5 seconds from exposure. (Photoreceptor surface resistance is used as a parameter). It is a figure which shows the calculation result of the latent image electric potential obtained by the model type | formula in this invention. Calculation results after 1 second from exposure. It is a figure which shows the shape of the latent image obtained with the latent image measuring apparatus used by this invention. Measurement data after 2 seconds from exposure to start of measurement (before ozone back). It is a figure which shows the shape of the latent image obtained with the latent image measuring apparatus used by this invention. Measurement data after 2 seconds from exposure to start of measurement (after ozone flashing). It is a figure which shows the calculation result of the latent image electric potential data obtained by the model type | formula in this invention. Calculation results after 2 seconds from exposure. (Photoreceptor surface resistance is used as a parameter). It is a figure which shows the calculation result of the latent image electric potential obtained by the model type | formula used by this invention. Calculation result after 0.11 second has elapsed after exposure. (Photoreceptor surface resistance is 1 × 10 ¹⁴ Ω / □). It is a figure which shows the example of the optical power profile (thickness direction) of the line beam for latent image pattern formation of the latent image measuring device used by this invention. The image output result of the photoconductor used in Example 2 of the present invention before ozone bubbling. The image output result after ozone bubbling of the photoreceptor used in Example 2 of the present invention.

Claims (3)

Means for measuring the shape of the electrostatic latent image as an electric potential with respect to the electrostatic latent image formed on the surface of the photosensitive member, and the surface resistance of the surface of the photosensitive member as the movement of the electric charge in the electrostatic latent image A method for specifying the surface resistance of the photoreceptor in combination with means for calculating by numerical calculation of a model formula using elapsed time as a parameter,
The time required from the exposure writing to the start of measurement in the measurement is used as the elapsed time from the writing in the numerical calculation, and the numerical calculation of the latent image using the measurement result of the latent image and the photoreceptor surface resistance as parameters. A photoreceptor surface resistance value is determined from the result, and the surface resistance value and the time from exposure to development of the image forming apparatus on which the photoreceptor is mounted are used to calculate the shape of the latent image under the conditions, A method for predicting image breakage in an image forming apparatus of a photoreceptor. The method for predicting image distortion according to claim 1, wherein the means for measuring the shape of the latent image is a means capable of evaluating a resolution of 1 line / mm or more in the atmosphere. 2. The method for predicting image distortion according to claim 1, wherein the means for measuring the shape of the latent image is a measurement method using a light attenuation function of a photosensitive member.

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