JP5332705B2 - Image evaluation method and apparatus / image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achive an image evaluation method which evaluates an electrostatic latent image formed in accordance with input information, in relation to the input information. <P>SOLUTION: The image evaluation is performed as follows. An optical image is written to a charged photoconductive photoreceptor 157 on the basis of input information having at least information about the shape and area of an input pattern, to form a corresponding electrostatic latent image 161 corresponding to the input pattern, and the area of the corresponding electrostatic latent image 161 is measured, and an area difference between the area of the input information and the area of the corresponding electrostatic latent image 161 is measured. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an image evaluation method and apparatus / image forming apparatus, and more particularly to an electrostatic latent image and a toner image in image formation using an electrophotographic process, and improvement of image formation using these evaluations.

  Conventionally, image formation using an electrophotographic process has been widely performed as an image forming apparatus such as an optical printer such as an analog copying machine, a digital copying machine, or a laser printer.

  In the electrophotographic process, a “photoconductive photosensitive member” is used to explain the image forming by the optical scanning that has become the mainstream recently and the optical writing using the light emitting diode array.

  The surface of the photoconductive photoconductor is uniformly charged, and “optical image writing” is performed on the uniformly charged photoconductor surface by optical scanning or the like.

  In the photoconductor portion irradiated with light by this optical image writing, “photoconductivity” occurs, the charging voltage is attenuated, and “electrostatic latent image” is formed on the surface of the photoconductor as “potential distribution corresponding to the written image”. It is formed.

The formed electrostatic latent image is visualized as a “toner image” by development using fine particles called toner.
The toner image obtained by visualizing the electrostatic latent image is generally transferred onto a sheet-like recording medium (hereinafter referred to as “recording sheet”) and then fixed to the recording sheet.

  The quality of image formation is determined by how well an image to be written (referred to as an original image) is reproduced as a toner image. In this case, “good reproduction” does not necessarily mean that “the formed image is faithful to the original image”.

  For example, considering the case where an original document to be copied is read by a scanner to generate an image signal, and an electrostatic latent image is formed by optical scanning with this image signal, the original document image is not necessarily “ideally good. The image is not necessarily an “image”, and there are an image that is rubbed or dirty, and an image that is not sufficiently dark.

  In such a case, the read image information signal is appropriately processed to generate an image signal so as to improve the image quality of the original image, and image writing is performed using this image signal.

  Thus, an image signal used to form an electrostatic latent image is called “input information”.

  Then, the quality of image formation is determined by “how faithful an image can be formed with input information”. The formed image is called an “output image”.

  Between the input signal and the output image, a process for forming an electrostatic latent image, a development process for using the formed electrostatic latent image as a toner image, and a transfer / fixing process for transferring and fixing the toner image on a recording sheet These processes affect the quality of the output image finally obtained. However, the greatest influence on the quality of the output image is the quality of the electrostatic latent image and the quality of the toner image.

  Therefore, in order to achieve good image formation, in the electrophotographic process, “how faithful the electrostatic latent image formed in response to the input signal is with respect to the input signal” and “ It is preferable to evaluate how faithful the toner image that has been visualized is.

  However, at present, only “comparison between input information and output image (toner image)” remains.

  The electrostatic latent image formed on the photoconductive photoreceptor in the electrophotographic process is, as the name suggests, a latent image that cannot be seen directly with the naked eye, but is visualized as a toner image. Visible.

  Although the electrostatic latent image is not directly visible with the naked eye as described above, the applicant first displays the electrostatic latent image on a display so that the latent image can be visually confirmed, and the potential of the electrostatic latent image is also reduced. A technique capable of measuring distribution and the like has been proposed (Patent Document 1).

  Evaluation of the reflection characteristics and gradation of the toner image on the recording sheet is known from Patent Documents 2, 3 and the like.

  The present invention has been made in view of the above-described circumstances, and realizes an image evaluation method capable of image evaluation of an electrostatic latent image formed according to input information in relation to input information, and further, a toner as an output image. Realization of an image evaluation method capable of evaluating an image in relation to an electrostatic latent image, realization of an image evaluation apparatus for implementing these methods, and utilization of image evaluation realized in this way for image formation Let it be an issue.

According to the first aspect of the present invention, there is provided an image evaluation method for performing a photo image writing on a charged photoconductive photoconductor on the basis of input information having at least information on a shape and an area of an input pattern and corresponding to the input pattern. A corresponding electrostatic latent image is formed, an area of the formed corresponding electrostatic latent image is measured, and an area difference between the area of the input information and the area of the corresponding electrostatic latent image is measured ”.

  As described above, the input information includes at least “input pattern shape and area information”.

The photoconductive photosensitive member is uniformly charged, and a “corresponding electrostatic latent image” having a shape and area corresponding to the “shape and area of the input pattern” is formed by optical image writing based on the input information.
As “optical image writing”, writing by optical scanning or image writing using a light emitting element array can be used.

  The “information constituting the input pattern” for writing the optical image, that is, “input information” can be generated by, for example, a computer. Alternatively, an image signal obtained by reading a visible pattern image having an area / shape set as input information with a scanner or a signal obtained by appropriately processing the image signal can be used as “input information”.

  In the image evaluation method according to the first aspect, as described above, the area of the corresponding electrostatic latent image formed manually according to the input pattern is measured, and the area of the input pattern (given as part of the input information). The area difference is measured.

  The closer the area difference is to 0, the more the corresponding electrostatic latent image is considered to be faithful to the input pattern.

  The area of the input pattern can be given as “one of the generated data” if the input information is generated by a computer or the like. In addition, when a predetermined pattern is read by a scanner and used as part of the input pattern information, the area is known by counting the number of light receiving elements constituting the pattern image on the scanner. Can do.

  The shape of the input pattern can be given as “emission information for each pixel” in optical image writing.

  The measurement of the area of the corresponding electrostatic latent image will be described later with reference to a specific example.

The image evaluation method according to the first aspect provides the input pattern with gradation.

That is, “ N corresponding electrostatic latent images corresponding to N (≧ 2) input patterns PI having different gradations I are formed, and the area of the corresponding electrostatic latent image MI corresponding to the input pattern PI: SI Then, the area difference of the input pattern PI from the area: SPI is measured for each gradation: I as follows.

That is, the area: SPI of the input pattern PI is linearly changed with respect to the gradation: I, and the area: SI of the corresponding electrostatic latent image MI: “area: SPI straight line” of “change with respect to the gradation: I”. Measure the "difference with respect to change".

An image evaluation apparatus according to claim 2 is an apparatus for performing the image evaluation method according to claim 1 , wherein the charging means, the input information generating means, the corresponding electrostatic latent image forming means, the area measuring means, Arithmetic processing means.
“Charging means” is means for charging a photoconductive photoreceptor. As the charging means, conventionally known non-contact type devices such as a corona discharger, contact type devices such as a charging brush and a charging roller, and “charged particle scanning method” which will be described later in the embodiment. Things "etc. can be used suitably.

  The “input information generating means” is means for generating input information of an input pattern to be applied to the photoconductor, for example, based on a computer that directly generates input information or a reading signal obtained by reading the above-described image with a scanner. A configuration that generates input information can be used as appropriate. Of course, the input information is generated including at least “information on the shape and area of the input pattern”.

  The “corresponding electrostatic latent image forming unit” is a unit that performs “optical image writing based on input information” on a uniformly charged photoconductor to form a corresponding electrostatic latent image corresponding to the input pattern. For example, an optical scanning device or the like can be used.

  “Area measuring means” is means for measuring the area of the corresponding electrostatic latent image. The area measuring means will be described in detail with reference to examples.

The “arithmetic processing means” uses the measured area of the corresponding electrostatic latent image and performs arithmetic processing including at least a difference from the area of the input pattern (given as input information).
The arithmetic processing performed by the arithmetic processing means is an operation for obtaining “ the area of the corresponding electrostatic latent image MI : the gradation of SI: the difference between the change with respect to I and the area: the linear change with SPI” .

The image evaluation method according to claim 3 is the following method.
An optical image is written on the charged photoconductive photoconductor based on input information having at least information on the shape and area of the input pattern to form a corresponding electrostatic latent image corresponding to the input pattern. Measure the area of the corresponding electrostatic latent image.
On the other hand, a visible-image electrostatic latent image is formed with the same input information as the input information, and the formed visible-image electrostatic latent image is visualized with toner to form a toner image. The area of the toner image Measure.

  Then, the difference between the area of the corresponding electrostatic latent image and the area of the toner image is measured.

  The corresponding electrostatic latent image and the visible electrostatic latent image are formed on the same photosensitive member or the same type of photosensitive member. The “same type of photoconductor” is a photoconductor that forms “corresponding electrostatic latent images of at least the same area” by optical image writing with the same input information, and is a different photoconductor. In this case, the input information when forming the corresponding electrostatic latent image and the input information when forming the visible latent image are “same in content”, but optical image writing is This is done for “different photoconductors”. At this time, since the contents of the input information are the same, the corresponding electrostatic latent image and the visible latent image have the same area and shape.

  In other words, the input information that makes the corresponding electrostatic latent images formed on the different photoconductors and the visible latent electrostatic image the same is the “contents that are identical in content”, If the latent image is visualized as a toner image, the visualized toner image is the same as the toner image obtained by visualizing the electrostatic latent image for visible image.

  In the case of “same photoconductor”, a corresponding electrostatic latent image is formed on the same photoconductor, and this corresponding electrostatic latent image can also be an electrostatic latent image for a visible image. Of course, the corresponding electrostatic latent image and the visible electrostatic latent image can be formed as separate electrostatic latent images using the same input information separately for the same photosensitive member. .

The image evaluation method according to claim 3 also forms N corresponding electrostatic latent images corresponding to N (≧ 2) input patterns having different gradations: I, and these N corresponding electrostatic latent images. MI area: SI is measured, and N visible image electrostatic latent images formed by input information having the same contents as the N input patterns are visualized with toner to obtain N toner images TI. The area: STI of the toner image TI can be measured, and the area: SI and STI can be measured for each gradation: I ( claim 4 ).

5. The image evaluation method according to claim 4 , wherein the input pattern PI is changed according to the gradation: I (N ≧ I ≧ 1), and the area: SI of the corresponding electrostatic latent image MI is linear with respect to the gradation: I. The N electrostatic latent images for visible image formed by the input patterns having the same contents are visualized with toner to obtain N toner images TI, and the area: STI of the toner images is measured. area: SI gradation: changes to the I, tonality area STI: can be configured to measure the difference with respect to changes to I (claim 5).

An image evaluation apparatus according to claim 6 is an apparatus for performing the image evaluation method according to any one of claims 3 to 5 , wherein the charging means, the input information generating means, and the corresponding electrostatic latent image forming means. And an area measuring unit, a visible image forming unit, a visible image area measuring unit, and an arithmetic processing unit.

“Charging means” is means for charging a photoconductive photoreceptor.
The “input information generating means” is means for generating input information of an input pattern that acts on the photoconductor.

  The “corresponding electrostatic latent image forming unit” is a unit that performs optical image writing on the photoconductor based on the input information to form a corresponding electrostatic latent image corresponding to the input pattern.

  “Area measuring means” is means for measuring the area of the corresponding electrostatic latent image.

  The “visible image forming means” forms an electrostatic latent image for visible image using input information having the same contents as the input pattern for forming the corresponding electrostatic latent image by the input information generating means. It is means for visualizing the electrostatic latent image as a toner image with toner.

  The “visible image area measuring unit” is a unit that measures the toner image area of the toner image formed by the visible image forming unit.

  The “arithmetic processing means” uses the corresponding electrostatic latent image area measured by the area measuring means and the toner image area measured by the visible image area measuring means, and at least “corresponding electrostatic latent image area and toner image area” "Calculation processing including difference between".

The image forming apparatus according to the present invention is an “image forming apparatus using an electrophotographic process”, and the image evaluation method according to any one of claims 1, 3 , 4 , and 5 , or claim 2 or 6 . The image forming conditions are adjusted and controlled according to at least one of the area difference information between the input information obtained by the image evaluation apparatus and the corresponding electrostatic latent image and the area difference information between the corresponding electrostatic latent image area and the toner image area. It has a control means to do ( claim 7 ).

As described above, according to the present invention, a novel image evaluation method, apparatus, and image forming apparatus can be realized.
According to the image evaluation method and apparatus of the present invention, in image formation using an electrophotographic process, the difference between the input information and the area of the corresponding electrostatic latent image corresponding thereto is measured, so that the relationship with the input pattern is obtained. Image evaluation of the electrostatic latent image becomes possible. Alternatively, the area of the corresponding electrostatic latent image and the area of the toner image obtained by visualizing the electrostatic latent image for visible image formed by the input pattern having the same input information as the input information for forming the corresponding electrostatic latent image Is measured, the toner image can be evaluated in relation to the corresponding electrostatic latent image corresponding to the input pattern.

  Such image evaluation can be used to improve the quality of image formation.

It is a figure for demonstrating one Embodiment of an image evaluation apparatus. It is a figure for demonstrating an example of a structure of a photoconductive photoconductor. It is a figure for demonstrating the optical scanning device as an example of an optical image writing means. It is a figure for demonstrating input information and a corresponding electrostatic latent image. It is a figure for demonstrating the area measurement of a corresponding electrostatic latent image. It is a figure for demonstrating optical image writing for forming a corresponding | compatible electrostatic latent image. It is a figure explaining an example of an input pattern. It is a figure explaining the relationship between the input information from which a gradation differs, and a corresponding electrostatic latent image. It is a figure which shows an example of an input pattern. It is a figure which shows mutually equivalent input information. It is a figure for demonstrating the relationship between a gradation and an area. FIG. 6 is a diagram for explaining area measurement of a toner image. It is a figure which shows the preferable example of the "lightness reproducibility" in gradation reproducibility. It is a figure explaining a response | compatibility with a corresponding electrostatic latent image and a toner image. It is a figure which shows the relationship between an electrostatic latent image area and a toner image area. 1 shows a system diagram of an example of an apparatus that performs image evaluation of a corresponding electrostatic latent image and a toner image with respect to input information. FIG. It is a diagram showing a process of searching for optimum and suitable values by feeding back the result of image evaluation to a control factor. FIG. 14 is a graph in which “brightness with respect to gradation: L *” shown in FIG. 13 is obtained by standardizing lightness L * with its maximum value. It is a figure which shows the graph which "normalized the area of the corresponding electrostatic latent image formed with this input information with respect to the gradation corresponding to input information" with the maximum value. It is a figure explaining a dot area rate. It is a figure for demonstrating an example of an image forming apparatus.

FIG. 1 shows an embodiment of an image evaluation apparatus.
Reference numeral 151 indicates a “casing in which the charging unit, the corresponding electrostatic latent image forming unit, and a part of the area measuring unit are accommodated”.

  In the casing 151, an electron gun 152, a condenser lens 153, a scanning lens 154, an objective lens 155, a light irradiation optical system 156, a sample stage 164, and an electron detector 163 are housed. Reference numeral 157 is a sample of “photoconductive photoreceptor”.

  Reference numeral 159 denotes a vacuum pump, reference numeral 158 denotes an interface, and reference numeral 160 denotes a control means. The vacuum pump 159 depressurizes the inner space of the casing 151 to a “low pressure state close to vacuum (hereinafter referred to as“ substantial vacuum state ”or simply“ vacuum state ”)”.

  The control unit 160 includes a computer and a display. The computer controls the entire apparatus via the interface 158, performs arithmetic processing related to image evaluation, and displays the calculation result on the display. In FIG. 1, reference numeral 161 schematically indicates “state of corresponding electrostatic latent image” displayed on the display.

  A sample 157, which is a photoconductive photoconductor, is formed in a flat plate shape in FIG. 1 and is planarly placed on the sample stage 164. The sample stage 164 causes three independent directions (vertical direction in the drawing, in the drawing). In the casing 151, the position can be adjusted three-dimensionally.

  The photoconductive photoconductor constituting the sample 157 can have various forms, but a general configuration is a configuration in which a photoconductive layer is formed on a conductive substrate. The photoconductive layer may have a single layer structure, or may be a so-called “function separation type” in which a charge generation layer and a charge transport layer (or a protective layer) are laminated. Further, it may be a single-layer photoreceptor using a material in which a charge generating substance and a charge transporting substance are mixed.

  The form of the photoconductive photoconductor as the sample is not limited to the flat shape shown in FIG. 1, but may be a drum shape or a belt shape. That is, “a drum-like one or a belt-like one actually used in the image forming apparatus” can be used as a sample as appropriate.

As an example of the photoconductive photoconductor as a sample, the function separation type will be briefly described with reference to FIG.
In recent years, the use of “organic photoconductive photoconductor (hereinafter referred to as“ OPC ”)” has become the mainstream from the viewpoint of low cost and easy processing.
In the OPC shown in FIG. 2, an intermediate layer (not shown) is provided on a conductive substrate 121, and a charge generation layer 122 and a charge transport layer 123 are formed thereon. It is the structure laminated | stacked in order.
In this configuration, the surface of the photoconductor is negatively charged, but a configuration in which the stacking order of the charge generation layer and the charge transport layer is reversed is also possible, in which case the surface of the photoconductor is charged to the positive polarity. .

  When the surface of the charge transport layer 123 is “negatively uniformly charged” and irradiated with light 124, the light 124 transmitted through the charge transport layer 123 is incident on the charge generation layer 122 and is positively coupled with electrons 126 in the charge generation layer 122. A hole 127 is generated.

  The generated electrons 126 are repelled by the negative charges charging the surface of the charge transport layer 122 and absorbed by the conductive substrate 121. At this time, a positive charge that balances with the negative charge that charges the surface of the charge transport layer 123 is induced in the “interface portion with the charge generation layer 122” of the conductive substrate 121, and the electrons 126 are attracted. To do.

  The hole 127 is attracted by the negative charge that charges the surface of the charge transport layer 122 and moves in the direction of the arrow 125 in the charge transport layer 123 to cancel the negative charge on the surface of the charge transport layer 123. A two-dimensional electrostatic latent image is formed on the surface of the photoreceptor by irradiating light 124 two-dimensionally and writing an optical image.

  The thickness of the charge generation layer 122 is generally about “sub-μm”, and the thickness of the charge transport layer 123 is generally “several tens of μm”. The pattern of the electrostatic latent image to be formed is a character / image, but “the minimum unit is a dot”.

  Returning to FIG. 1, the “charging unit” includes an electron gun 152, a condenser lens 153, a scanning lens 154, and an objective lens 155.

  As the electron gun 152 and the various lenses constituting the charging means, for example, those used for scanning electron microscope can be used. As the electron gun, an appropriate one such as a hot filament type or a field emission can be used.

In charging the surface of the sample 157 set on the sample stage 164, the inside of the casing 151 is sucked by the vacuum pump 159, and the inside of the casing is decompressed to a vacuum state.
In practice, a plurality of vacuum pumps 159 such as a rotary pump, a turbo molecular pump, and an ion sputtering pump can be used in combination depending on the degree of vacuum to be achieved.

The condenser lens 153, the scanning lens 154, and the objective lens 155 are all “magnetic lens” or “electrostatic lens”.
While the electron beam emitted from the electron gun 152 is converged on the surface of the sample 157 by the condenser lens 153, the scanning lens 154, and the objective lens 155, the electron beam is two-dimensionally scanned on the sample 157 by the scanning lens 154. The surface of 157 is uniformly charged.

Instead of the electron gun 152, an “ion particle beam” can be generated using an ion gun for charging. For example, if an ion gun that generates Ga ⁺ is used as ion particles that form an ion stream, the surface of the sample can be positively charged, and a photoconductive photoreceptor having a positive charge characteristic can be charged. .

  When the surface of the sample 157 is charged using the electron gun 152, the charged potential of the sample surface mainly depends on “electron acceleration voltage and irradiation time”. The higher the electron acceleration voltage, the higher the charged potential of the sample surface. .

  In order to evaluate the electrostatic latent image, the electrostatic latent image formed on the sample surface is equivalent to the electrostatic latent image formed in the actual “image formation using an electrophotographic process”. There is a need.

  In order to form an electrostatic latent image equivalent to such an “electrostatic latent image actually formed in image formation” on the sample 157, “acceleration voltage is about 1.0 to several kV”, “ Adjust the irradiation time in the range of tens of seconds to several tens of minutes. The charged potential of the sample charged in this way is a value measured by using a “general-purpose surface potential meter” of about “−600 to −1000 V (equivalent to the charged potential in an actual image forming apparatus such as a copying machine). "

  That is, the charging conditions are changed in advance to obtain charging conditions that can realize the above-described charging potential, and charging is performed under these conditions.

  Adjustment of the charging condition is performed by the above-described computer via the interface 158.

  The charging potential can be adjusted by adjusting the bias voltage by applying a “bias voltage to the sample” instead of changing the acceleration voltage or adjusting the acceleration voltage.

  “Light image writing” is performed on the uniformly charged sample 157 by the light irradiation optical system 176 to form an electrostatic latent image.

The light irradiation optical system 176 constitutes “corresponding electrostatic latent image forming means”.
As the light irradiation optical system 176, a known optical scanning device or “optical image writing device using a light emitting element array” can be used as appropriate.
As an example of the light irradiation optical system 176, a conventionally well-known optical scanning device will be described with reference to FIG.
Hereinafter, such a light irradiation optical system is also referred to as “optical image writing means”.

  As shown in FIG. 3, the optical scanning device causes the laser beam emitted from the light source 111 to enter the collimating lens 112 through an aperture (not shown) to be converted into a parallel beam, and is collected by the cylindrical lens 113 in the sub-scanning direction. The light is incident on the deflecting / reflecting surface of the polygon mirror 115 through the first mirror 114, and is formed in the vicinity of the deflecting / reflecting surface into a long line image in the main scanning direction.

  A deflected light beam obtained by rotating the polygon mirror 115 at a constant speed is condensed on a drum-shaped photoconductor 119 via a scanning imaging lens (so-called fθ lens) and a bending mirror 118 to form a light spot, The light spot is scanned with the bus direction of the photoconductor as the main scanning direction to perform “main scanning”. Further, sub-scanning is performed by rotating the photosensitive member 119 around the rotation shaft 1191 at a constant speed.

The surface of the photoconductor 119 is uniformly charged by an appropriate charging means (not shown), and a two-dimensional electrostatic latent image is formed by the optical scanning.
In FIG. 3, reference numeral 1192 indicates three types of “electrostatic latent images with dot patterns (one dot is exaggerated and drawn greatly)” on which an image is written by optical scanning.

  As the light source 111, a laser diode (LD) can be used, and a light emitting diode (LED) or a vertical surface emitting laser (VCSEL) can also be used.

  A VCSEL can be used to perform “multi-beam scanning with minute scanning line intervals”, and a high-resolution electrostatic latent image can be formed in a short time.

  In FIG. 1, the sample 157, which is a photoconductive photoconductor, is “flat” unlike the drum-shaped photoconductor 119 shown in FIG. Thus, two-dimensional scanning is realized by moving the sample 157 at a constant speed in a direction parallel to the surface of the sample and perpendicular to the main scanning direction of optical scanning.

  As described above, the form of the “photoconductive photosensitive member as a sample” is not limited to the flat shape shown in FIG. 1, but can be a drum shape or a belt shape. In this configuration, instead of the sample stage 164 and the sample 157, a drum-shaped photoconductor 119 and a rotation driving means for rotating the drum-shaped photoconductor 119 shown in FIG.

  When such a drum-shaped sample is used, the above-described general-purpose surface potential meter is incorporated in the casing 151, and the potential of the “sample surface charged by the charging means” is measured while rotating the sample. it can.

The light scanning condition is preferably, for example, an LD having a wavelength of 650 nm as a light source and an exposure energy density of “1 mJ / cm ² or less per dot”. By performing light scanning under such conditions, per dot Area: about 5000 μm ² can be written.

  In FIG. 1, the light irradiation means 156 is provided in the casing 151, but this portion is disposed outside the casing 151, an opening is formed in the casing 151, and the opening is sealed with glass having high transmittance. And you may make it perform optical scanning with the light from the outside through this glass.

  Next, the measurement of the electrostatic latent image will be described. For the measurement of the electrostatic latent image, the above-described charging means and the electron detector 163 are used.

  The current value from the electron gun 152 is reduced to “a few pA, which is about 1/1000 compared to the time of charging (several nA)”, and the surface of the sample 157 is two-dimensionally scanned with such a “weak electron beam”.

  The reason why the current value of the electron beam is reduced in this way is to prevent the electrostatic latent image from disappearing rapidly if the current value of the electron beam of the current value is large.

  The electron detector 163 is a “secondary electron detector”. When the sample 157 is two-dimensionally scanned with a weak electron beam for measuring an electrostatic latent image, secondary electrons are emitted from the sample 157. The amount of secondary electrons emitted is “the portion where the electrostatic latent image is formed”. However, it is often “parts where no electrostatic latent image is formed”.

  Therefore, the secondary electrons generated are detected by the electron detector 163 while two-dimensionally using a weak electron beam (the secondary electrons attracted into the electron detector 163 are applied to the phosphor to generate fluorescence, and the intensity of the fluorescence is reduced. To obtain a signal corresponding to the electrostatic latent image. This measurement is known from Patent Document 1.

  In this way, the detection signal from the electronic detector 163 is taken into the computer of the control means 160 via the interface 158, and data processing is performed to display the pattern of the electrostatic latent image on the display. FIG. 1 shows a state in which three types of electrostatic latent images 161 formed on the sample 157 are displayed on the display.

  A description will be given of a case where the image evaluation method according to claim 1 is performed by the image evaluation apparatus as shown in FIG. 1. After setting the sample 157 on the sample stage 164, each part of the apparatus is controlled by the computer of the control means 160. The casing 151 is evacuated by the vacuum pump 159, the surface of the sample 157 is uniformly negatively charged as described above, and an electrostatic latent image is formed by optical scanning (optical image writing) by the light irradiation optical system 156. .

  At this time, input information having “the shape and area of the input pattern” is generated in the computer of the control unit 160, and optical image writing by the light irradiation optical system 156 is performed using this input information as “optical image writing information”. By this optical image writing, a “corresponding electrostatic latent image” corresponding to the input information is formed.

An example of the input information and the corresponding electrostatic latent image is shown in FIG.
FIG. 4A shows an “input pattern having input information”, in which 16 “length of one side: a square” are arranged in 4 × 4 (4 rows × 4 columns), and four of them are black.
With respect to the total area of the input pattern: 16a ² , the total area of the black portion is 4a ² and the “area ratio of the black portion with respect to the total area: 16a ² ” is 25%.
When the total area: 16a ² is white, “gradation: zero”, and when the total area is black, gradation: 15, a total of 16 gradations can be expressed. The gradation in the case shown in FIG. 4 ".
Thus, “the input information includes at least the shape of the input pattern (an arrangement pattern of black and white portions) and area”.

  The length of one side of the square: a is arbitrary, but this is determined by “a desired resolution to be realized in image formation using an electrophotographic process”.

  For example, considering 600 dpi as the desired resolution, the length of one side of a square in the input pattern: a = 42.3 μm, resolution: 1200 dpi, a = 21.17 μm, and 2400 dpi resolution, a = 10.58 μm. Become.

  If the gradation to be expressed is 256 gradations, an array of at least 16 × 16 (= 256) squares is required. In order to express gradation more smoothly, a larger number of square arrays are required.

According to the input information of the input pattern shown in FIG. 4A, the electrostatic latent image formed on the sample 157 as described above is a “corresponding electrostatic latent image” corresponding to the input pattern. The electrostatic latent image is, for example, as shown in FIG.
In this example, the “electrostatic latent image portion corresponding to one black square” of the input pattern is an “elliptical shape”, but may actually be a circle, a shape close to a rectangle, or “ It may become a more complicated shape.

The size of the electrostatic latent image portion (line image portion corresponding to one black square in the input pattern in the corresponding electrostatic latent image) is also a square of one side: a as shown in FIG. In some cases, the size protrudes, and as shown in FIG.
The area of the electrostatic latent image portion: Sd is Sd> a ² in the case of FIG. 4C, and Sd <a ² in the case of (d).

Area of the electrostatic latent image portion: for a Sd ≠ a ^2, the gradation of the corresponding electrostatic latent image, a desired value: deviated from 4.

  Thus, “the gradation of the corresponding electrostatic latent image is different from the gradation in the input pattern” impairs “the gradation reproducibility of the visible image” when the corresponding electrostatic latent image is visualized as a toner image. It becomes a cause.

  In the corresponding electrostatic latent image, the size of the electrostatic latent image portion corresponding to “one black square portion” of the input pattern is the irradiation light intensity, irradiation time, photoconductor characteristics, charging potential, etc. in optical image writing. Therefore, the size of a dot (an electrostatic latent image portion corresponding to one black square portion) can be changed by changing the values of these control factors.

  Therefore, it is possible to improve gradation reproduction by feeding back the “area difference” between the area of the corresponding electrostatic latent image and the area of the input pattern to the electrophotographic process of image formation by image evaluation.

For example, in the case shown in FIG. 4A, the area information of the input pattern is given as the size of one “black square” of the input pattern: a ² . It is necessary to measure the area of the corresponding electrostatic latent image (the area of the “electrostatic latent image portion” corresponding to the one dot).

This area measurement will be described with reference to FIG.
In FIG. 5A, reference numeral 20 corresponds to “one side length: a square” in the input pattern shown in FIG. 4A, and reference numeral 21 denotes one dot in the corresponding electrostatic latent image. An outline of an electrostatic latent image portion (an electrostatic latent image corresponding to the one square) is shown.
Reference numeral 22 in FIG. 5A denotes one pixel representing “minimum unit of measurement resolution”.
One pixel is a square of one side length: p, and “p <a”.
In FIG. 5A, “a = 12p” is used. However, the present invention is not limited to this, and is suitable for expressing the shape of the corresponding electrostatic latent image (the shape of the one-dot electrostatic latent image portion in the example being described). Any number can be used.
In FIG. 5, the entire pixel has a pixel arrangement of “16 × 16”, but in this figure, “part of the corresponding electrostatic latent image” is cut out, and the whole is, for example, about 720 × 480 pixels. is there.
The resolution of the measuring device is such a resolution as long as it is a standard of NTSC (National Television Standards Committee) using a scanning electron detector.
FIG. 5 shows an “electrostatic latent image portion of only one dot”, but as shown in FIGS. 4 (a) and 4 (b), in the case of “simultaneously measuring surrounding dots”, at least 48 × 48 pixels are required.

  The detecting means (electronic detector) of the measuring device converts the intensity of the obtained physical quantity into gradations and outputs an image (for example, 256 gradations).

  As described above, the corresponding electrostatic latent image has gradation, and, for example, the number of gradations is different between the center and the periphery of the electrostatic latent image portion in FIG. Therefore, a threshold value is provided for gradation, and “binarization” is performed by setting the electrostatic latent image portion to zero and the background portion to one. By this binarization, the contour of the corresponding electrostatic latent image (part) can also be determined clearly.

  The area of the corresponding electrostatic latent image may be obtained by counting the number of pixels of “gradation: 0” in the corresponding electrostatic latent image binarized in this way. In the example of the electrostatic latent image portion shown in FIG. 5B, the area is 120 pixels.

  On the other hand, since the square of one side: a in the input pattern is composed of 144 pixels, the difference in the number of pixels from the number of pixels: 120 representing the area of the corresponding electrostatic latent image corresponding to this square is 24 pixels. .

That is, the area of the corresponding electrostatic latent image is an area ratio: 83.3% with respect to the area of the input pattern. Further, when 120 pixels corresponding to the area of the corresponding electrostatic latent image portion of 1 dot are converted into a square shape, one side of the converted square is “0.91a ² ”.

  If the area ratio of the corresponding electrostatic latent image: 100% is an ideal value, the actual corresponding electrostatic latent image is 16.7% smaller. Thus, by measuring the area of the corresponding electrostatic latent image corresponding to the input pattern, the difference between the input information and the corresponding electrostatic latent image can be grasped.

In the above case, the gradation of the corresponding electrostatic latent image is approximately 3.3 with respect to the gradation of the input pattern: 4, and the “gradation shift” of the corresponding electrostatic latent image with respect to the input pattern is reduced. Can be estimated.
FIG. 5B shows an “electrostatic latent image portion of 1 dot”, but “the above difference” is similarly obtained when the corresponding electrostatic latent image has 4 dots as shown in FIG. 4B. .

  In the case of having 4 dots, the difference between the input information and the corresponding electrostatic latent image may be “same in error range”, but may be different from the error.

  In the evaluation of all four dots, the difference can be obtained by taking the sum of the four dots or “taking the average value”. The same applies when the number of dots increases.

As shown in FIG. 6A, in an input pattern composed of 4 × 4 squares, an array of 16 squares is numbered as numbers 1 to 16 as shown.

Optical image writing is performed by “optical scanning in the order of squares 1 to 16”, and “1 (ON)” is set when light is irradiated, and “0 (OFF)” is set when no light is irradiated.
Then, on / off of the light irradiation at the time of optical image writing of the input pattern shown in FIG. 6B is “1,0,1,0,0,0,0,0,1,0,1,0, 0, 0, 0, 0 ".

  This is information that gives the shape of the input pattern. Of course, the actual total number of sequences is much more than 16.

  In the above description, the optical scanning device described as the optical image writing means has a single light source, and the optical scanning is performed by so-called “single beam scanning”, but the input is performed by multi-beam scanning using a plurality of light sources. Needless to say, a corresponding electrostatic latent image of the pattern may be formed.

  For example, using two light sources, the 4 × 4 input pattern is divided into odd and even rows, and the on / off signal of one light source is “1,0,1,0,1,0,1, 0 ", optical scanning of odd rows is performed, and the ON / OFF signal of the other light source is set to" 0, 0, 0, 0, 0, 0, 0, 0 ", and the input pattern of FIG. Can write. Four rows of optical scanning can be performed at a time by multi-beam scanning using four light sources.

  In the above example, the time required for optical scanning between adjacent dots is constant. When a laser diode (LD) is used as the light source and optical image writing is performed using a polygon mirror, the above time is determined by the light emission time of the LD and the rotation speed of the polygon mirror, which is one of the control factors of the electrophotographic process.

  In the electrostatic latent image measuring method described in Patent Document 1, only “dot evaluation” is evaluated. However, in the present invention, as in the above embodiment, the input of halftone dots constituting the input pattern is performed. The difference between the value and the area of the electrostatic latent image portion can be measured.

  When performing the above evaluation using the apparatus shown in FIG. 1, each means is controlled by the computer 160 via the interface 158. Detailed control of each means is performed by software in a computer.

The data / image processing described with reference to FIG. 5 is performed by a computer, and the difference from the area / area ratio / input pattern of the corresponding electrostatic latent image is obtained.
Operations such as data processing / image processing and “area difference calculation” are not special, and can be performed using general-purpose data / image processing software.

There may be “apparatus restrictions” for the image evaluation apparatus.
For example, there are constraints such as “the electron beam scanning range cannot be widened” or “the size of the sample (photoconductive photoconductor) is limited”.
Regarding the scanning range of the electron beam, it is possible to scan a certain range (several mm × several mm) at the expense of “resolution of several nm” compared to a general-purpose SEM, but it is actually used. Many photoreceptors have a “diameter: several centimeters, longitudinal direction: several tens of centimeters in the form of a drum”.
It is difficult to scan the entire surface of such a photoconductor at once, and the partial scan is repeated by moving the photoconductor. Further, if a photoconductor having such a size is used as a sample, the “part where the sample is set” becomes large and the vacuum chamber needs to have a large capacity. Therefore, it is necessary to devise measures such as measuring a part of an actual photoconductor by cutting out a sample. In this case, the scanning of the electron beam can be performed in a very narrow range.

"Concrete example"
A function-separated type “photoconductive photoreceptor” used in a commercially available electronic copying apparatus or laser printer was cut into “about 2 cm × 2 cm” and used as a sample.
The thickness of CTL is about 30 μm.

  The sample surface was uniformly charged with an acceleration voltage of the electron beam of 1.8 kV.

  As the “input pattern”, a “2 × 2 array of 1 side: a square” shown in FIG. 7 was adopted, and optical image writing was performed by an optical scanning device of the type shown in FIG. Optical images were written by multi-beam scanning in which two LDs having an emission wavelength of λ = 650 nm were used as light sources and two lines were scanned simultaneously.

The first row is written with the laser beam from one of the two LDs, and the second row is written with the laser beam from the other LD. Therefore, the light source on / off signal for writing the first row is “1,0”, and the light source on / off signal for writing the second row is “0, 0”.
The exposure energy density was 1 mJ / cm ² or less.

  The time required for writing one dot by the deflection by the polygon mirror: T is set to T / 2 (duty ratio: 50%).

The area measurement as described above was performed about 30 times, and the area of the corresponding electrostatic latent image (1 dot in the black portion) was determined to be “5600 ± 100 μm ² ”.
The area of the input pattern was 1792 μm ² with a resolution of 600 dpi as a target value, and the area difference from the corresponding electrostatic latent image was 3808 μm ² .

  As described above, the measurement of the “area difference between the input pattern and the corresponding electrostatic latent image” for a certain gradation is important for improving the gradation reproducibility. Since it is established between “different gradations”, it is necessary to grasp the difference between the different gradations.

  Referring to FIG. 8 (5), the upper diagram in FIG. 8 shows input information of “three input patterns with different gradations”, and a corresponding electrostatic latent image is formed based on this input information. As shown by the arrows, the order of formation may be the order of gradations: 4 (upper left figure in FIG. 8), 8 (middle figure in the same figure), 12 (right figure in the same figure), or vice versa.

  The formation position of the corresponding electrostatic latent image may be the same position or a different position on the photoconductive photoconductor as a sample. In the case of forming at the same position, a static eliminating means for erasing the previously formed corresponding electrostatic latent image is required.

  Static elimination can be performed, for example, by irradiating the entire surface of the sample with “light having the same wavelength as that used for optical image writing”. For example, a light emitting element (LED) is disposed close to the sample installation position and the entire surface of the sample is disposed. May be irradiated with light. The emission wavelength of the LED may be set to λ = 650 nm, for example, in consideration of the photosensitivity characteristics of the sample. After neutralization, the sample is charged again and a corresponding electrostatic latent image is formed by optical image writing.

  The lower diagram of FIG. 8 shows corresponding electrostatic latent images corresponding to the three types of input patterns shown in the above diagram. The areas of the three types of corresponding electrostatic latent images thus formed are measured in the same manner as in the above example, and the difference from the area of each input pattern (determined for each input pattern as input information) is obtained. .

  In this way, in FIG. 8, the area difference is obtained for the input pattern of three gradations (the left diagram, the middle diagram, and the right diagram in the upper diagram of FIG. 8). In the example of FIG. 8, the number of gradations is set to “3” for simplicity of explanation. However, in the actual case, if the required number of gradations is, for example, 256 (16 × 16), the input pattern and its input There are 256 types of information, and the corresponding electrostatic latent image is formed and the area is measured 256 times.

  An input pattern having a large arrangement as shown in FIG. 9 is used. However, the required number of gradations may be thinned out to 128, 64, 32, 16 or the like.

Each of the input patterns in FIG. 8 is a 4 × 4 array, but the “8 × 2” array shown on the right side of FIG. 10 is also equivalent to the “4 × 4 array” on the left side of FIG.
If the input pattern is “8 × 2” shown on the right side of FIG. 10, each corresponding electrostatic latent image can be formed by one-line scanning using a multi-beam scanning method of two-line simultaneous scanning using two LDs as light sources.

  In this way, “evaluation of gradation reproducibility” becomes possible at the level of the corresponding electrostatic latent image.

The area of the input pattern (in the above example, “a set of black square portions”) linearly increases or decreases with respect to “the number of necessary gradations” in the input information of the input pattern.
FIG. 11 shows a graph created with the horizontal axis representing gradation and the area of the input pattern representing the vertical axis.
In FIG. 11, “input information” relates to an input pattern.

In this input information, “area (vertical axis)” is calculated with a resolution of 600 dpi. The slope of a straight line representing input information: 1792.1 is represented by the area / gradation of the input pattern, and the intercept is zero and passes through the origin.
If an ideal corresponding electrostatic latent image can be formed, the change in area of the corresponding electrostatic latent image with respect to the gradation coincides with this “straight line of input information”.
However, in practice, as described above, the dot (electrostatic latent image portion) area of the corresponding electrostatic latent image deviates from the area value of the input information. For example, as shown in FIG. 4D, when one dot of the corresponding electrostatic latent image fits in a square of one side: a and the area is “smaller than a ² ”, the area for the gradation The change is as shown by “electrostatic latent image 1” in FIG.

In this case, “the area of one dot of the corresponding electrostatic latent image” is 0.833a ² . The slope of this straight line is 1243.5, which is different from the slope of the straight line representing the input information. Therefore, this can be measured as “deviation of input information from a straight line”.
The straight line of the electrostatic latent image 1 in FIG. 11 passes through the origin.

Next, considering the case of the corresponding electrostatic latent image having the number of gradations of 12 shown in FIG. 8 (lower right diagram in FIG. 8), the area of one dot in the corresponding electrostatic latent image is “smaller than a ² ”. However, dots that are vertically adjacent to each other overlap each other. There are a total of 12 dots constituting the corresponding electrostatic latent image.
If the area of one dot is “Sd”, the total area: 12Sd is ideal, but since the dots overlap each other, the total area becomes “smaller than 12Sd”.
As the number of dots constituting the corresponding electrostatic latent image increases and “the number of overlapping dots increases”, the area of all dots constituting the corresponding electrostatic latent image decreases. Therefore, the relationship between gradation and area in this case is a graph line (broken line) like “electrostatic latent image 2” in FIG.
Strictly speaking, the graph line “electrostatic latent image 2” is not a straight line but an “approximate straight line”.

A straight line representing “electrostatic latent image 2” has an inclination of 1173.8, which is different from “inclination of a straight line representing input information (1792.1)”, and has an intercept of 1577.1 μm ² . Therefore, as “deviation from input information”, “intercept” can be measured in addition to “inclination”.

In FIG. 11, the correlation coefficient of the graph line of “input information” is 1 and is “straight line” (this is called “ideal straight line”).
Next, when the correlation coefficient of the graph line of “electrostatic latent image 1” is obtained, it is 1, which is also a straight line, but “inclination deviation” from the ideal straight line. The correlation coefficient of the graph line of “electrostatic latent image 2” is 0.9956, and it can be seen that it is slightly deviated from the straight line. This is also one form of “deviation between the input information and the area of the corresponding electrostatic latent image” and can be measured.

That is, in claim 1 , when the area: SPI of the input pattern PI is linearly changed with respect to the gradation: I, the area: SI of the corresponding electrostatic latent image MI “changes with respect to the gradation: I”. In this case, “the difference with respect to the linear change in the area SPI” is three of the inclination, the intercept, and the correlation coefficient of the approximate straight line (the electrostatic latent image 1 and the electrostatic latent image 2).

  When an image is printed on paper as a printed matter, “lightness: L *” is often used for tone reproducibility evaluation of the printed image. It is known that the “lightness difference between adjacent gradations” that can be perceived by human beings takes a constant value regardless of the lightness, and thus “change in lightness with respect to gradation is linear” is preferable. The same can be said for the area of the electrostatic latent image, and it is preferable that the area of the electrostatic latent image changes linearly with respect to the gradation.

A corresponding electrostatic latent image (FIG. 4B) is formed on the basis of the input pattern of FIG. 4A, and the corresponding electrostatic latent image is developed to form a toner image “finally output image on recording sheet” If the size of the toner particles constituting the “output image” is “extremely exaggerated”, the image is as shown in FIG.
Of course, since the particle diameter of the toner is 10 μm or less, the individual toner particles cannot be visually observed, and it does not mean that “a large number of large gaps are left between the toner particles” as shown in the figure.

The “dot-like toner image” as shown in FIG. 12A can be observed in detail using an optical microscope, a laser microscope, or the like. An imaging device such as a digital camera is attached to the microscope, and the observation image is converted into electronic data. Then, it becomes easy to perform subsequent data / image processing.
If general-purpose image processing software is used, the “area of the toner image” can be easily obtained.

For example, the area can be obtained by extracting the outline of the toner image, which is the “output image” obtained as shown in FIG. 12B, through the corresponding electrostatic latent image from the input pattern. The method for obtaining this area is the same as that described with reference to FIG.
An area difference: Δs between the “area of the toner image” thus obtained and the corresponding electrostatic latent image obtained as described above can be obtained (FIG. 12C).

The formation of the electrostatic latent image corresponding to the input pattern and the toner image are preferably “simultaneously performed”.
The formation of the corresponding electrostatic latent image and the toner image may be performed by different means.
For example, a toner image is formed as an output image on a recording sheet by an appropriate digital copying apparatus or printer, while a corresponding electrostatic latent image is obtained by using the apparatus shown in FIG. It can be formed under the same conditions as the latent image formation (charging conditions such as charging potential, optical image writing by a scanning optical system, etc.).

  Of course, the photoconductive photosensitive member used for forming the corresponding electrostatic latent image and the photosensitive member forming the toner image by development have the same physical properties (the same electrostatic latent image is formed by forming the electrostatic latent image under the same conditions). Those having characteristics as a photoreceptor on which an image is formed are used. Of course, the corresponding electrostatic latent image can be formed and developed on the same photoconductor.

  The case where the same photosensitive member is used will be briefly described. As the photosensitive member as the sample described above, a “drum-shaped photosensitive member that is actually used in a digital copying apparatus” is used. Set the charging conditions and optical image writing conditions, and form the corresponding electrostatic latent image corresponding to the registered pattern and measure the corresponding electrostatic latent image (area Etc.).

  After that, the “same photoconductor” is set in a digital copying apparatus, and an electrostatic latent image is formed with the same input information as the above input pattern according to the above charging conditions and optical image writing conditions. And developing and transferring the formed electrostatic latent image for visible image to obtain a toner image corresponding to the input information. Then, the area measurement or the like is performed on the toner image as described above.

  By doing so, in addition to the relationship between the input information of the input pattern and the corresponding electrostatic latent image, it is possible to know the relationship between the corresponding electrostatic latent image and the toner image that visualizes this.

  Here, the toner for forming the toner image and the recording medium for transferring and fixing the toner image will be described.

  As a method for developing an electrostatic latent image, there are a dry development method and a wet development method, but at present, a “dry development method” having excellent high-speed performance is mainly used. However, the implementation of the present invention is not limited to the dry development method, and it is of course possible to use a wet development method.

“One-component developer and two-component developer” are known as powder developers used in the dry development system, and “non-magnetic toner” and “magnetic toner” are included in the toner constituting the one-component developer. The two-component developer includes “toner particles and carrier particles”. In this case, the toner includes non-magnetic toner and magnetic toner.
The toner particles have a polymer as a main component and a colorant and the like, and have a particle size of several μm to several tens of μm. The carrier particles are a metallic material such as iron powder and have a particle size of several tens to several hundreds of μm.

  The recording sheet that will ultimately carry the toner image is generally transfer paper, but it can also be cardboard, OHP sheets (plastic sheets for overhead projectors), and the like.

  Conventionally, tone reproducibility of a toner image on a recording sheet such as paper is macroscopically measured by measuring “reflectance, density, brightness, etc.”.

In particular, it is preferable that the “lightness reproducibility” in the gradation reproducibility changes linearly with a change in gradation on the horizontal axis, as shown in FIG.
The correspondence between the corresponding electrostatic latent image (the electrostatic latent image for visible image) and the toner image will be described with reference to FIG.
The upper diagram of FIG. 14 shows three types of corresponding electrostatic latent images having different gradations. This corresponding electrostatic latent image is the same as that shown in the lower diagram of FIG. 8, and is formed as a “static latent image for visible image” by the three types of input information shown in the upper diagram of FIG. .

  The lower diagram in FIG. 14 is a toner image (“toner image” in the figure) corresponding to the electrostatic latent image in the above diagram.

  As described above, the area of the electrostatic latent image and the area of the toner image are obtained for each gradation, and the difference between the “electrostatic latent image area and the toner image area” is obtained.

  In FIG. 14, the number of gradations is set to 3 for the sake of simplicity of description, but it is needless to say that the number of gradations is not limited to 256 and may be 256.

For example, in the case of measuring input information of 256 gradations, for example, input information of “16 × 16 array” as shown in FIG. 9 may be used. In this example, the total area of the black square portion is a 48a ^2, total area: area ratio 256a ^2: 18.8%, the gradation: is 48.

As described above, the area of the corresponding electrostatic latent image deviates from the “area of input information”. Therefore, the area of the toner image formed using the corresponding electrostatic latent image is generally “further shifted” from the area of the input information.
Considering the case where the toner “ideally adheres to the electrostatic latent image” using “corresponding electrostatic latent image as a reference” instead of the input information, the toner image has the same area as the corresponding electrostatic latent image. This case is represented by a graph line represented by “A” in FIG.

  The horizontal axis in FIG. 15 represents the electrostatic latent image area, and the vertical axis represents the toner image area (“toner image area” in the figure). In the ideal case, since the electrostatic latent image area and the toner image area are the same, the slope of the graph line A is “1”, the intercept is 0, and the coordinate origin is passed.

  “Slope” is “area / area” and is dimensionless. In FIG. 15, the area is calculated by taking the case of resolution: 600 dpi as an example.

The area of the electrostatic latent image portion corresponding to one dot of the input image (one dot-like portion in the corresponding electrostatic latent image) was 83.3% of the area of the input information.
A graph line “B” in FIG. 15 shows a case where toner adhesion to the visible electrostatic latent image equivalent to the corresponding electrostatic latent image is small and the toner image area is 70% of the corresponding electrostatic latent image area. Show. The graph line “B” passes through the origin with an inclination of 0.7.

  Therefore, the difference in inclination between the graph line “A” and the graph line “B” with the inclination of 1 is “0.3”, which is one of the “difference between the corresponding electrostatic latent image and the toner image”.

  The graph line “C” in FIG. 15 shows the case of a toner image having “± several percent area variation” at random with respect to the corresponding electrostatic latent image. An approximate straight line obtained by approximating the graph line “C” with a straight line indicated by a broken line has an inclination of 1.0957, and a deviation (difference) of 0.0957 from the graph line “A” having an inclination of 1.

The intercept of the approximate line is −1412.2, which is one of the differences between the corresponding electrostatic latent image and the toner image.
In this way, the input pattern PI is changed according to the gradation: I (N ≧ I ≧ 1), the area: SI of the corresponding electrostatic latent image MI is linearly changed with respect to the gradation: I, and the same contents N visible image electrostatic latent images formed by the input pattern are visualized with toner to form N toner images TI, and the area: STI of the toner images is measured. The gradation of area: SI: The slope, intercept, and correlation coefficient can be measured as the difference from the change in I to the change in area STI.

  Conventionally, the “evaluation of gradation reproducibility” was based only on the linearity of the brightness of the toner image with respect to the input information. However, according to the present invention, the “deviation between the electrostatic latent image and the toner image in the gradation reproducibility” is used. High-precision measurement is possible.

  FIG. 16 shows a system diagram of an example of an apparatus that performs image evaluation of a corresponding electrostatic latent image and a toner image with respect to input information.

  In FIG. 16, portions denoted by reference numerals 141 and 145 perform image evaluation similar to that described with reference to FIG. 1, and are formed by forming a corresponding electrostatic latent image on the sample in the portion denoted by reference numeral 141. The area of the corresponding electrostatic latent image is measured in the same manner as in FIG.

  In FIG. 16, reference numeral 142 denotes an image forming unit that performs image formation by an electrophotographic process, and the “electrostatic latent image forming condition” is set to be the same as that of a sample on which the corresponding electrostatic latent image is formed and the area is measured. A photoreceptor is used.

  Input information related to the input pattern is generated by the computer 145 and displayed on the display. In this way, a corresponding electrostatic latent image is formed on the sample based on the input information, and its area is measured.

  On the other hand, the image forming unit 142 charges the photoconductor under the same conditions as the sample, performs optical image writing under the same conditions as the optical image writing on the sample, and generates an electrostatic latent image for visible image corresponding to the input information. A toner image formed and developed is transferred and fixed on a recording sheet such as paper and output as an output image.

  Therefore, the same electrostatic latent image as the “corresponding electrostatic latent image formed on the sample at the portion where image evaluation is performed” is formed on the photosensitive member of the image forming unit 142 and visualized as a toner image. The area of the corresponding electrostatic latent image formed on the sample is measured, and the difference from the area of the input information is taken. This difference in area is performed for each gradation having a desired number of gradations.

  As the image forming unit 142, a commercially available optical printer or digital copying apparatus may be used.

  In FIG. 16, reference numeral 146 denotes a toner image formed on the recording sheet in accordance with the input information. In the figure, three different gradations are illustrated, but it is needless to say that the number of gradations may be larger for the sake of simplicity.

  The toner image 146 in FIG. 6 depicts a macroscopic size of several mm to several cm. When viewed in a microscopic size such as several tens of μm, the toner image 146 is small as illustrated in FIG. It is made up of a set of dots.

  The evaluation of the pattern 146 using the toner image will be described.

The pattern 146 by the toner image is measured by two types of observation / measurement devices.
The first observation / measurement means 143 is an apparatus that “mainly measures the reflectance of the pattern”. Basically, it has a light source 148 and a detector 149, and the measurement sample 150 is irradiated with light from the light source 148, and the reflected light is detected by the detector 149.

  The measurement sample 150 is a recording medium having a toner image pattern 146. In this apparatus, the reflectance of the measurement sample 150 is measured, but instead of measuring the reflectance, “lightness” may be measured together with the reflectance.

  The second observation / measurement means 144 is a “microscope” and observes / measures the microscopic state of the same measurement sample 150. That is, the former in the first and second observation / measurement apparatuses performs “macroscopic observation / measurement”, and the latter performs “microscopic observation / measurement”.

  As described above, the input information specifying the input pattern is generated by the computer 145, the corresponding electrostatic latent image is formed and observed by the apparatus 141, the observation result is returned to the computer 145, and image formation is performed using the same input information. The toner image 146 is formed on a recording medium such as paper by the unit 142, the observation / measurement is performed by the first and second observation / measurement means 143, 144, the observation result is returned to the computer 145, and the computer 145 The area difference between the corresponding electrostatic latent image and the toner image is calculated. The formation of the corresponding electrostatic latent image and the formation and observation of the toner image may be performed simultaneously or with a time difference.

In this way, it is possible to measure and evaluate the input information and the corresponding electrostatic latent image, the corresponding electrostatic latent image and the toner image, and the difference / deviation between the input information and the toner image with high accuracy.
It is assumed that the function having input information is F ₀ , the corresponding electrostatic latent image corresponding to this is represented by F ₁ , and the toner image is represented by F ₂ .

At this time, the difference between the input information and the corresponding electrostatic latent image: ΔF ₁ is represented by F ₁ −F ₀ , and the difference between the corresponding electrostatic latent image and the toner image image: ΔF ₂ is represented by F ₂ −F ₁ . Is done.

Conventionally, a difference between input information and a toner image: ΔF ₀ = F ₂ −F ₀ has been obtained. Here, ΔF ₀ = ΔF ₁ + ΔF ₂ .
There are many control factors (parameters, conditions) in the electrophotographic process between the input information and the finally corresponding toner image. As in the prior art, if only the difference between the input information and the toner image: ΔF ₀ , the efficiency of searching for suitable control factors (parameters, conditions) for the electrophotographic process is poor.

ΔF ₁ is “difference between input information and corresponding electrostatic latent image”, and mainly relates to “control factor related to scanning optical system”. ΔF ₂ is “difference between corresponding electrostatic latent image and toner image”, and mainly relates to “control factor relating to development”.

In the image evaluation of the present invention, what was previously based on “ΔF ₀ only” can be evaluated by “using _two of ΔF ₁ and ΔF ₂ ”, and the process can also separate the scanning optical system and the development system. The efficiency of searching for control factors can be effectively improved .

Consider further gradation for the above function.
When a certain gradation is expressed as “i”, the above F ₀ , F ₁ , and F ₂ are F _0i , F _1i , and F _2i with respect to gradation: i. _These differences are ΔF _0i , ΔF _1i , and ΔF _2i , respectively, and F and ΔF may be obtained in the range of gradation: i (for example, 0 ≦ i ≦ 255).

  FIG. 17 is a diagram showing a process for feeding back the measurement result to the control factor and searching for the optimum / preferred value. Such a feedback means may be incorporated into the electrophotographic process.

  Further, if the system of FIG. 16 is applied, an inspection system for the image forming unit 142 can be obtained. Measurements, evaluations, and adjustments can be performed by fixing the parts other than the image forming unit 142 and sequentially changing the parts of the image forming unit 142.

  Thus, in addition to the input information and the toner image, the result of “evaluation including an electrostatic latent image” is reflected in the control factor, and thus an apparatus capable of forming such an image together with “an image with better gradation reproducibility” Can be realized.

"Concrete example"
FIG. 13 shows a preferable example of “lightness reproducibility” in the case of gradation reproducibility (when the lightness changes linearly with a change in gradation on the horizontal axis). FIG. 18 shows a graph in which the lightness of the key is “L *” and the lightness L * is “normalized by the maximum value”.
In FIG. 18, for example, it is assumed that a value 192 deviating from the straight line 191 is obtained at the gradation: 100, and “deviation from the straight line 191” of this value 192 is denoted as “ΔL * ′”.

ΔL * is “standardized brightness difference”.
FIG. 19 shows a graph in which the area of the corresponding electrostatic latent image formed by the input information is “normalized by the maximum value” with respect to the gradation corresponding to the input information.
This graph represents a case where the area of the corresponding electrostatic latent image “ideally increases with respect to gradation”.

  In this figure, it is assumed that, for example, at the gradation of 100, the area of the corresponding electrostatic latent image is “value shifted from the straight line 201: 202”. At this time, if the value “202” is “ΔS ′” as the “deviation from the straight line 201”, this “ΔS ′” is the ideal “standardized area of the corresponding electrostatic latent image area” at the gradation: 100. It is the difference from the value.

Further, when the difference between the brightness difference and the corresponding electrostatic latent image area: ΔL * ′ − ΔS ′ is obtained, this represents the contribution of toner image formation in the development process, and includes ΔF ₂ and measured as described above. Each value of the difference / deviation is combined with the evaluation method based on the brightness of the prior art.
The evaluation of the entire gradation is “ΔL _i * ′ − ΔS _i ′” where the gradation is i.

  Conventionally, gradation reproducibility is evaluated by plotting “the number of gradations on the horizontal axis and the measured value of lightness on the vertical axis” to perform linear approximation, and evaluating “excellence or inferiority of gradation reproducibility” by the value of the correlation coefficient However, there was a problem with the evaluation method because there was only one evaluation value.

  On the other hand, as in the present invention, in addition to the correlation coefficient, by adding “slope deviation of approximate line” and “intercept value (deviation from the origin)” to the evaluation value, a more accurate evaluation method Can be realized.

  In addition, by reflecting the obtained evaluation result on the control factor of the electrophotographic process, it is possible to realize an image quality with better gradation reproducibility and an image forming apparatus that forms the image quality.

  In the evaluation apparatus described with reference to FIG. 16, a case is considered where the reflectance of a toner image is measured to obtain a halftone dot area ratio: At.

As is well known, the tone reproducibility of a toner image expressed on a recording sheet is often evaluated by measuring the reflectance: R. When expressed by optical density: D, the relationship between reflectance: R and optical density: D is
D = log ₁₀ (1 / R)
It is represented by

  When there is no toner on the white recording medium, the density is “0”, and the density in a so-called “solid image” in which the entire recording medium is covered with toner often takes a value of about 2.0.

  The toner image formed by the electrophotographic process using optical image writing is a so-called halftone dot image by “a set of dots”, and the area ratio of the halftone dots is 0% with respect to density: 0 for a certain area. The solid image is 100%, and the number of gradations (the number of gradations) is determined by “how many different densities can be expressed” during this period.

  In FIG. 20A, assuming that the reference area is Ss and the dot image area in the toner image is Sd, the dot area ratio: At in the toner image is given by “At = Sd / Ss”.

  Conventionally, the halftone dot occupancy of the toner image is measured in the reflectance measurement. In this case, “optical dot gain (measurement light penetrates and diffuses into the recording medium paper). Or the reflection on the toner surface or multiple scattering inside the toner, which has the effect of increasing the measured halftone dot area).

  The relationship between the area gradation and the halftone dot area ratio is expressed by the “Murray-Davis equation”, and there is a Yule-Niesen equation in which the optical dot gain: n is corrected. In principle, the dot area ratio includes an optical dot gain.

In recent years, when a sentence / image is electronically created by a personal computer (PC) and an output image is output using a laser printer or a digital copying apparatus, generally 256 gradations (8 bits, 2) are used. ⁸ ) is used, and this is the number of required gradations, but it depends greatly on the performance of information equipment and electronic equipment and the level of image forming technology. For image formation for business use, a larger number of gradations is required, and it is considered that the number of gradations will further increase in the future.

  In the image evaluation apparatus as shown in FIG. 16, area measurement is performed not only on the toner image but also on the corresponding electrostatic latent image.

  As shown in FIG. 20A, the dot area ratio: At (= Ss / Sd) based on the reflectance of the toner image includes an optical dot gain: n. However, as shown in FIG. When the area of one dot image of the electrostatic latent image: Se is measured and the halftone dot area ratio: As (As = Se / Ss) with respect to the electrostatic latent image is obtained, the area measurement in this case is not an optical measurement. Area ratio: As does not include optical dot gain.

  Therefore, from the halftone dot area ratio measured optically: At and the halftone dot area ratio measured non-optically: As: (At-As) or ratio: (At / As), the optical dot gain: n can be obtained, and the dot area ratio: At can be corrected effectively.

  The image (toner image) formed by the electrophotographic process has control factors (parameters and conditions) such as the photosensitive member charging potential, light intensity and irradiation time when writing an optical image, and the amount of toner attached to the electrostatic latent image. Controlled by

  In the present invention, the area of the corresponding electrostatic latent image formed by the input information of the input pattern, which is the pattern to be imaged, and the dependency of this area on the gradation are measured. Since the area of the visualized toner image and its dependency on the gradation are measured, it becomes possible to set the control factors of the above-mentioned electrophotographic process more precisely and perform better control with these control factors. And good image formation can be realized.

  FIG. 21 is an explanatory view showing one form of the image forming apparatus.

  In FIG. 21, a photoconductor (OPC) 71 is uniformly charged by a charging charger 72 while rotating at a constant speed in the direction of an arrow, and an optical image is written by a scanning beam 73 to form an electrostatic latent image.

  The formed electrostatic latent image is visualized by a toner 74 to become a toner image, electrostatically transferred by a transfer charger 76 onto a transfer sheet 75 as a recording medium, and the transfer sheet 76 to which the toner image is transferred is transferred by a fixing device 77. The toner image is fixed and discharged outside the apparatus.

  The surface of the photoreceptor 71 after the toner image transfer is cleaned by a cleaner 78 and discharged by a charge removing lamp 79.

  By controlling the charging potential of the charger 72, the light intensity and irradiation time during optical image writing, the developing conditions such as the bias voltage and toner charge amount in the developing device, etc., according to the control factors determined as described above. Good image formation can be performed.

152 electron gun
153 condenser lens
154 Scanning lens
155 Objective lens
157 Sample (photoconductive photoreceptor)
159 vacuum pump
158 interface
160 Control means
165 Light irradiation optical system
164 Sample stage
163 Electronic detector

JP 2003-295696 A Japanese Patent No. 3865676 JP-A-2005-311952

Claims (7)

Based on input information having at least information on the shape and area of the input pattern on the charged photoconductive photoreceptor, optical image writing is performed to form a corresponding electrostatic latent image corresponding to the input pattern, In the image evaluation for measuring the area of the corresponding electrostatic latent image and measuring the area difference between the area of the input information and the area of the corresponding electrostatic latent image, N (≧ 2) pieces having different gradations: I N corresponding electrostatic latent images corresponding to the input pattern PI are formed, and an area difference between the area: SI of the corresponding electrostatic latent image MI corresponding to the input pattern PI and the area: SPI of the input pattern PI is defined as follows: Tone: An image evaluation method for measuring every I,
The area SPI of the input pattern PI is linearly changed with respect to the gradation I, and the area SPI of the corresponding electrostatic latent image MI is linearly changed with respect to the gradation I. An image evaluation method comprising measuring a difference with respect to. An apparatus for carrying out the image evaluation method according to claim 1,
  Charging means for charging the photoconductive photoreceptor;
  Input information generating means for generating input information of an input pattern to be applied to the photoreceptor;
  Corresponding electrostatic latent image forming means for performing optical image writing on the photoreceptor based on the input information to form a corresponding electrostatic latent image corresponding to the input pattern;
  Area measuring means for measuring the area of the corresponding electrostatic latent image;
  An image evaluation apparatus, comprising: an arithmetic processing unit that performs an arithmetic process including at least a difference from the area of the input pattern using the measured area of the corresponding electrostatic latent image. Based on input information having at least information on the shape and area of the input pattern on the charged photoconductive photoreceptor, optical image writing is performed to form a corresponding electrostatic latent image corresponding to the input pattern,
  Measure the area of this corresponding electrostatic latent image,
  Form an electrostatic latent image for visible image with the same input information as the input information,
  The formed electrostatic latent image for visible image is visualized with toner to form a toner image, the area of this toner image is measured,
  An image evaluation method comprising measuring a difference between an area of the corresponding electrostatic latent image and an area of the toner image. The image evaluation method according to claim 3,
  N corresponding electrostatic latent images corresponding to N (≧ 2) input patterns PI having different gradations I are formed, and the area: SI of these N corresponding electrostatic latent images MI is measured.
  The N latent images for visible image formed by the input information having the same contents as the N input patterns PI are visualized with toner to form N toner images TI. Measure and
  An image evaluation method, wherein area: SI and STI are measured for each gradation: I. The image evaluation method according to claim 4,
  The input pattern PI is changed according to the gradation: I (N ≧ I ≧ 1), the area: SI of the corresponding electrostatic latent image MI is linearly changed with respect to the gradation: I,
  The N electrostatic latent images for visible image formed by the input patterns having the same contents are visualized with toner to obtain N toner images TI, and the area: STI of the toner images is measured.
  A method of evaluating an image, comprising measuring a difference of a change in the area: SI gradation: I with respect to a change in the area STI. An apparatus for performing the image evaluation method according to any one of claims 3 to 6,
  Charging means for charging the photoconductive photoreceptor;
  Input information generating means for generating input information of an input pattern to be applied to the photoreceptor;
  Corresponding electrostatic latent image forming means for performing optical image writing on the photoreceptor based on the input information to form a corresponding electrostatic latent image corresponding to the input pattern;
  Area measuring means for measuring the area of the corresponding electrostatic latent image;
  A visible image that forms an electrostatic latent image for visible image using input information having the same contents as the input pattern by the input information generating means, and visualizes the electrostatic latent image for visible image as a toner image with toner. Forming means;
  Visible image area measuring means for measuring the toner image area of the toner image formed by the visible image forming means;
  Using the corresponding electrostatic latent image area measured by the area measuring unit and the toner image area measured by the visible image area measuring unit, an operation including at least a difference between the corresponding electrostatic latent image area and the toner image area An image evaluation apparatus comprising arithmetic processing means for performing processing. In an image forming apparatus using an electrophotographic process,
  Area difference information between the input information obtained by the image evaluation method according to claim 1, or the image evaluation apparatus according to claim 2, and a corresponding electrostatic latent image, An image forming apparatus comprising control means for adjusting and controlling image forming conditions according to at least one of area difference information between a corresponding electrostatic latent image area and a toner image area.

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