JP2011064722A - Image evaluation method, image evaluation device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image evaluation method for realizing uniformization of an electrostatic latent image, and an image evaluation apparatus and an image forming apparatus to which this evaluation method is applied.
SOLUTION: A plurality of light sources 11, drive means for emitting light sources 11, electrostatic latent image forming means for forming an electrostatic latent image on a photosensitive member with laser light emitted from the light source 11, and laser light Mean intensity and peak intensity correction means, an optical power meter 13 for measuring variations in the intensity of emitted light between a plurality of light sources 11 arranged, and a detector 13 are provided. The average intensity of the emitted light is corrected based on the intensity variation of the emitted light between the light sources 11, and a plurality of electrostatic latent images are formed on the photoconductor to evaluate the uniformity of the electrostatic latent image.
[Selection] Figure 1

Description

  The present invention relates to an image evaluation method for realizing uniformization of an electrostatic latent image, and an image evaluation apparatus and an image forming apparatus to which the evaluation method is applied.

  In an electrophotographic process applied to a digital copying machine, a laser printer, etc., a vertical surface emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser) in which a plurality of light sources are arranged for the purpose of achieving high definition of optical writing. It has come to be used. As a result, it is possible to form an image with a high resolution of 1200 dpi, 2400 dpi, and even 4800 dpi from a conventional resolution of 600 dpi (dot per inch), thereby realizing a high quality image to be printed on paper.

  FIG. 4 shows a schematic view of a vertical surface emitting laser in which a plurality of light emitting sources are arranged, viewed from the optical axis (perpendicular to the paper surface). In the figure, a black circle represents a light source (light source) of one vertical surface emitting laser. The light emission direction is a direction perpendicular to the paper surface if it is parallel light. Since the vertical surface emitting laser is manufactured monolithically on a semiconductor substrate using a semiconductor process, an array of light emitting sources can be easily formed. The interval between the light source and the light source is about several tens of μm. The emission wavelength (λ) is, for example, 780 nm, and light in the infrared region can be output. In the figure, 30 (5 × 6) light sources are arranged. These light sources can be independently controlled by electrical control.

  In this way, in the electrophotographic process using multiple light sources, even if multiple light sources emit light with the same input signal, the light emission characteristics for each light source, specifically the variation in the amount of light generated and the light response waveform, are generated. Resulting in. This main cause is considered to be due to a manufacturing error of the vertical surface emitting laser. When the light amount varies among the plurality of light sources, the formed electrostatic latent image also varies.

  In order to cope with such a problem, as shown in Patent Document 1, correction is performed to keep the light output of each light source constant.

  By the way, in a digital copying machine, a laser printer, or the like, light emitted from a light source reaches a photosensitive member through a scanning optical system, and at that time, light loss due to absorption or vignetting of the optical member occurs. . Therefore, it is preferable that the correction of the light amount is performed not on the basis of the light source but on the surface of the photoconductor as the latent image forming position.

  In addition, variations in the size of the electrostatic latent image are not only caused by variations in the light emission characteristics of the light source, but also due to variations in the properties of the photoconductor, particularly reciprocity law failure. There is a need to.

  The present invention has been made in view of the above-mentioned problems, and corrects the influence due to the difference in the properties of each light source and the influence due to the reciprocity failure of the photosensitive member, thereby effectively varying the shape of the electrostatic latent image. It is an object of the present invention to provide an image evaluation method for achieving uniform suppression of electrostatic latent images and an image evaluation apparatus and an image forming apparatus to which the evaluation method is applied.

  (1) The present invention uses a vertical surface emitting laser having a plurality of arranged light sources, driving means for emitting the vertical surface emitting lasers with continuous light or pulsed light, and laser light emitted from the plurality of light sources. The electrostatic latent image forming means for forming an electrostatic latent image on the body, the means for correcting the average intensity and peak intensity of the laser beam, and the variation in intensity of the emitted light among the plurality of light sources arranged An intensity measuring means for measuring at the formation position and an electrostatic latent image measuring means for measuring an electrostatic latent image are provided, and electrostatic charges formed on the photosensitive member are determined based on measurement results obtained by the intensity measuring means and the electrostatic latent image measuring means. An image evaluation method for evaluating a latent image, wherein each light source is corrected by a correcting unit based on variations in intensity of emitted light between a plurality of light sources measured by an intensity measuring unit while continuously emitting a vertical surface emitting laser by a driving unit. Of light emitted from The intensity is corrected, and then a plurality of electrostatic latent images are formed on the photosensitive member while emitting a vertical surface emitting laser with pulsed light by the driving means, and this is measured by the electrostatic latent image measuring means. The most important feature is to evaluate the uniformity of the.

  Although not particularly limited in the present invention, it is preferable that the correction of the average intensity of the emitted light can be performed in a plurality of stages according to the intensity of the input signals to the plurality of light sources.

  Although not particularly limited in the present invention, it is preferable to measure the response waveform of the pulsed light for each of the plurality of light sources and correct the peak intensity of the light source that needs to be corrected based on the measured response waveform.

  Further, although not particularly limited in the present invention, it is preferable that correction of peak intensity can be performed in a plurality of stages according to the intensity of input signals to a plurality of light sources.

  Further, although not particularly limited in the present invention, a deflecting reflecting surface having a plurality of reflecting surfaces is provided, and electrostatic latent images are formed using different numbers of reflecting surfaces, respectively, and formed using different numbers of reflecting surfaces. Preferably, the shape of the electrostatic latent image thus measured is measured, and the output of the light source that needs to be corrected is corrected based on the comparison result of the shape of the electrostatic latent image on each reflection surface number.

  Although not particularly limited in the present invention, when forming an electrostatic latent image, a strip-shaped electrostatic latent image that is long in the main scanning direction on the surface of the photosensitive member by repeatedly supplying a pulsed input signal to the light source. When forming the image and measuring the electrostatic latent image, it is preferable to evaluate the electrostatic latent image based on the length of the belt-like electrostatic latent image in the sub-scanning direction.

  (2) The present invention is also an image evaluation apparatus for executing the image evaluation method according to the present invention, and is a vertical surface emitting laser having a charged particle generator for generating charged particles for charging a photoreceptor and a plurality of light sources. An optical system provided between the light source and the photosensitive body on the optical path of the outgoing light, an outgoing light measuring unit that measures the intensity of the outgoing light from each light source after passing through the optical system, An electrostatic latent image measuring unit for measuring the shape of the electrostatic latent image formed on the body, the intensity of the emitted light measured by the emitted light measuring unit, and the electrostatic latent image measured by the electrostatic latent image measuring unit. And a correction unit that corrects the output of the light source that needs correction based on the shape of the image.

  (3) The present invention is also an image forming apparatus including a photosensitive member on which an electrostatic latent image is formed by light emitted from a plurality of light sources, and evaluates the electrostatic latent image formed on the photosensitive member. As an image evaluation apparatus for this purpose, an image evaluation apparatus according to the present invention is provided.

  According to the present invention, the influence due to the difference in the properties of each light source and the influence due to the reciprocity failure of the photoreceptor are corrected, and the variation in the shape of the electrostatic latent image is effectively suppressed. An image evaluation method for realizing uniformization, and an image evaluation apparatus and an image forming apparatus to which the evaluation method is applied can be provided.

The Example of the image evaluation method which concerns on this invention is shown, (a) is the schematic of the whole measuring apparatus, (b) is a graph which shows the dispersion | variation in the emitted light intensity for every light source, (c) is based on Ich5 The graph which shows the ratio of the dispersion | variation in the emitted light intensity of each light source which was done, (d) is a graph which shows the emitted light intensity of each light source after correction | amendment. 1A and 1B show signal waveforms input to the light source of FIG. 1, wherein FIG. 1A shows continuous light, FIG. 1B shows pulse light when overshooting is performed, and FIG. 1C shows signal waveform of pulsed light when no overshooting is performed. Indicates. FIG. 3 is a schematic diagram illustrating a correction unit of the image forming apparatus according to the exemplary embodiment of the present invention. FIG. 4 is a schematic diagram showing a vertical surface emitting laser in which a plurality of light emitting sources are arranged in the image forming apparatus of FIG. 3. 4A and 4B are graphs showing variations in emitted light intensity from a light source in the image forming apparatus of FIG. 3, (a) and (b) are examples of the emitted light intensity before correction, and (c) is an output light intensity after correction. An example is shown. FIGS. 4A and 4B are diagrams illustrating examples of the shape of an electrostatic latent image measured by the image forming apparatus of FIG. 3. FIG. 5A illustrates a shape of the electrostatic latent image before correction and FIG. It is a graph which shows the relationship between the intensity | strength of the input signal of a vertical surface emitting laser, and light intensity, (a) shows the case of a single light source, (b) shows the case of a plurality of light sources. In the graph which shows the intensity | strength of the said input signal, (a) shows the example of the difference of the intensity | strength of each input signal, (b) shows the intensity | strength of each input signal in the some light source shown to (b) of FIG. It is a table | surface which shows the corrected amount of each input signal shown in FIG. FIG. 8B is a diagram illustrating the shape of an electrostatic latent image at the intensity of each input signal by the plurality of light sources in FIG. 7B, where FIG. 7A is before correction of the input signal intensity, and FIG. 7B is after correction of the intensity of the input signal. The shape of the electrostatic latent image is shown. The structure and function of the response waveform measuring means in the image forming apparatus of FIG. 3 are shown. (A) is a schematic diagram of the response waveform measuring means and the waveform of the input signal, and (b) is the response waveform. 11 shows a measurement result by the response waveform measuring means of FIG. 11 when an input signal having overshoot is input to the light source, where (a) shows the waveform of the input signal having overshoot, and (b) shows the peak intensity of the overshoot. The measurement result when it is appropriate, (c) shows the measurement result when the peak intensity of the overshoot is inappropriate. It is a graph which shows the light emission characteristic of a several light source, (a) shows the intensity | strength of the response waveform of each light source before correction | amendment, (b) shows the intensity | strength of the response waveform of each light source after correction | amendment. It is a graph which shows a mode that the overshoot of the input signal with respect to a certain light source is changed, (a) shows the intensity | strength of each overshoot, (b) shows the response waveform intensity | strength of the output based on the input signal which has each overshoot. FIG. 3 is a schematic diagram illustrating a correction unit of the image forming apparatus according to the exemplary embodiment of the present invention. It is a graph which shows a mode that the response waveform of a several light source is corrected, (a) is the intensity | strength of the response waveform of each light source before correction | amendment, (b) is the intensity | strength of the overshoot for correcting the response waveform of each light source. , (C) shows the intensity of the response waveform after correction. It is a table | surface which shows the example of the correction amount of average intensity | strength with respect to each of a several light source, and peak intensity. It is a graph which shows a mode that the peak intensity of an input signal is changed in three steps. It is a figure which shows the shape of an electrostatic latent image when changing peak intensity, (a) is a rectangular electrostatic latent image serving as a reference, and (b) to (d) are static when the peak intensity is increased in order. The shape of the electrostatic latent image is shown. It is an example of a reference table when there are three light sources and the peak intensity can be changed in three stages. It is a figure which shows the relationship between a peak intensity | strength and the shape of an electrostatic latent image, (a) shows the case where an electrostatic latent image is formed in an ideal shape, (b) shows the case where distortion arises in the shape. It is a figure which shows the electrostatic latent image formed using the several light source, (a) is only 1 surface of a polygon mirror, (b) is formed by deflecting the emitted light from a light source using 2 surfaces. Shows an electrostatic latent image. FIG. 6A is a diagram showing a shift in the writing position by each light source when forming an electrostatic latent image using a plurality of light sources, FIG. 5A is a diagram showing the shape of the electrostatic latent image in a state where the writing positions are aligned, and FIG. Is the shape of the electrostatic latent image when the writing position is shifted, (c) is the shape of the electrostatic latent image formed in a band shape, and (d) is the band-shaped electrostatic latent image of (c). In this case, the continuous pulse light input is shown. It is a figure which shows the example of the shape of the strip | belt-shaped electrostatic latent image formed using the several light source, (a) is only one polarization surface of a polygon mirror, (b) is deflecting using two polarization surfaces. The shape of the electrostatic latent image formed by this is shown. It is the schematic which shows an example of the scanning optical system using a vertical surface emitting laser. It is sectional drawing which shows the image measuring apparatus which concerns on a present Example. FIG. 2 is a schematic diagram illustrating the principle of forming an electrostatic latent image on a photoreceptor. It is a flowchart which shows the image evaluation method which concerns on a present Example.

  Embodiments of an image evaluation method, an image evaluation apparatus, and an image forming apparatus according to the present invention will be described below with reference to the drawings.

<Image evaluation apparatus and image evaluation method using the same>
Embodiments of an image evaluation apparatus according to the present invention will be described. In this embodiment, the intensity of the vertical surface emitting laser is measured as shown in FIG. In FIG. 1A, 11 is a vertical surface emitting laser, 12 is an optical system, and 13 is an intensity measuring means.

  The vertical surface emitting laser 11 is depicted in a simplified manner and with the optical axis seen from the side, but actually, as shown in FIG. 4, a plurality of light sources are arranged.

  The optical system 12 is drawn with only one lens to avoid complication, but is actually a scanning optical system composed of a plurality of optical elements as shown in FIG. The scanning optical system includes an after-mentioned photoreceptor and constitutes an electrostatic latent image forming unit.

  Specifically, the intensity measurement means 13 is an optical power meter. The optical power meter may be a commercially available general-purpose product. The optical power meter receives the light emitted from the light source by the light receiver and outputs the intensity in units W. The signal input to the light source is a continuous signal having an average intensity I as shown in FIG.

  The intensity measuring means 13 is installed at a position equivalent to the electrostatic latent image forming position. However, when the intensity measuring means 13 is actually provided in the image forming apparatus, if the photosensitive member is present at the electrostatic latent image forming position, the intensity measurement is performed. The means 13 cannot be installed. For this reason, a mechanical stage (not shown) is provided for allowing the photosensitive member to escape during intensity measurement. In addition, when forming an electrostatic latent image on the photosensitive member, a mechanical stage (not shown) is provided for allowing the intensity measuring means to escape.

  Note that setting of the input signal, electrical transmission of the input signal to the light source, and the like are performed by driving means (not shown).

  When the average intensity is measured for a plurality of light sources in the vertical surface emitting laser 11, the measurement result varies for each light source as shown in FIG. Here, only nine light sources are drawn to avoid complications (described as ch1 to ch9 in the figure), but the same applies even if the number of light sources is 20, 40, or more. Despite giving the same input signal to any light source, the intensity of the emitted light varies.

  Here, assuming that the measurement is performed with the optical element 12 removed, the variation in the intensity of the emitted light is caused by a manufacturing error of the vertical surface emitting laser. On the other hand, when the optical element 12 is placed, the influence of the optical element is also included. In the complicated scanning optical system shown in FIG. 24, it is conceivable that the intensity of a specific light source decreases due to vignetting by the optical system, light absorption by each member constituting the optical system, or the like. Therefore, it is important to measure the intensity of the emitted light at the electrostatic latent image forming position via the optical system.

  Next, correction for reducing variations in emitted light intensity will be described. Specifically, the correction is performed by changing the intensity of the input signal for each light source. That is, the average intensity I of the input signal indicated by 10 in FIG.

  First, the light source used as a reference is determined. For example, in FIG. 1B, with reference to ch5, the emitted light intensity of other light sources is adjusted to this. Compared with ch5, the emitted light intensity of ch1, ch3, ch4, and ch7 is small, that of ch6, ch8, and ch9 is large, and ch2 is the same. The intensity of light emitted from each channel is expressed as Ichi (i is 1 to 9), and the intensity ratio is expressed as Ich5 / Ichi with Ich5 as a reference. This is the correction amount (correction coefficient). The correction amount of each light source in this embodiment is 1.2 for ch1, 1.0 for ch2, 1.1 for ch3, 1.1 for ch4, 0.8 for ch6, 1.2 for ch7, and 0 for ch8. .9, ch9 is obtained as 0.8.

  These correction amounts are reflected in the input signal of FIG. Assuming that I in FIG. 1 (a) is for ch5, these correction coefficients may be applied to I (FIG. 1 (c)). When the corrected input signal shown in FIG. 1C is used, the intensity of light emitted from each light source can be made uniform as shown in FIG.

  The variation in the emission intensity is mainly caused by manufacturing errors, but there is an advantage of improving the apparent light source production yield by performing such correction rather than reducing the manufacturing errors.

  The continuous light, pulsed light, average intensity, and peak intensity used in this embodiment will be described with reference to FIG. FIG. 2 shows a signal waveform input to the light source.

  FIG. 2A shows a continuous light input signal. Here, the average intensity is I. t0 is the light emission start time. The light emission duration t1 may be a time required for measuring the average intensity, and is, for example, several seconds to several tens of seconds.

  FIG. 2B shows an example of an input signal of pulsed light. Here, the average intensity is I, and the peak intensity is I + Iov. The light emission time is from several ns to several hundreds ns from t0 to t2. The light emission time t0 to t1 of the peak intensity is several ns to several tens ns. The peak intensity is a so-called overshoot. In the continuous light shown in FIG. 2 (a), the peak intensity can be set. However, since the entire light emission time is extremely longer than the light emission time of the peak intensity, it is ignored as compared with the average intensity.

  FIG. 2 (c) shows an example of an input signal when overshooting is not performed with pulsed light. The time from t0 to t1 is about several ns to several hundred ns.

  The intensity of each incident signal described above is proportional to the current injected into the light source.

  An example of the correction means according to this embodiment is shown in FIG. First, in the personal computer (PC) 32, a correction amount (correction coefficient) table 31 for each light source is created as an electronic file. In the PC 32, an operation for multiplying the reference signal intensity by the correction amount based on the table 31 is performed. Using this result as an input signal, the vertical surface emitting laser 34 is caused to emit light through an electric circuit 33 (interface) that controls the vertical surface emitting laser 34. In FIG. 3, 35 indicates a scanning optical system, and 36 indicates intensity measuring means (similar to FIG. 1A).

  Due to poor adjustment of the scanning optical system, vignetting, and the like, the emission intensity as shown in FIGS. 5A and 5B may be obtained. Adjustments that take into account the effects of However, if the image evaluation apparatus and the image evaluation method according to the present embodiment are used, appropriate correction can be performed even when the influence of such an optical system is significant, as shown in FIG. Thus, the emitted light intensity can be made uniform.

Next, the evaluation of the electrostatic latent image will be described.
An electrostatic latent image is formed on the charged photoreceptor by a scanning optical system (electrostatic latent image forming unit), and the electrostatic latent image is observed and measured by an electrostatic latent image observation unit. The measured electrostatic latent image is schematically shown in FIG. A dot-shaped electrostatic latent image is formed using pulsed light. The pulse used is pulsed light as shown in FIG.

  FIG. 6A shows an electrostatic latent image formed in a state in which the intensity of light emitted from each light source varies as shown in FIG. . In this case, it can be seen that variation occurs in the size (area) of the electrostatic latent image. However, variations in the size of the electrostatic latent image are exaggerated.

  FIG. 6B shows an electrostatic latent image formed after correcting the intensity of the emitted light. If the average intensity of each light source is appropriately corrected, the sizes of the electrostatic latent images are completely the same. However, the photoconductor is assumed to be completely uniform.

Here, the determination of the variation in the area of the electrostatic latent image in the present embodiment will be specifically described.
First, in this embodiment, the areas of nine electrostatic latent images formed from nine light sources are respectively determined, and the average value is S (average) and the standard deviation is ΔS. The evaluation of the uniformity of the electrostatic latent image in this embodiment is based on this ΔS. The allowable range and tolerance of this value are finally determined as appropriate from the image quality of the toner image on the paper. For example, it is assumed that ΔS is uniform within ± 10%. In order to realize a high-quality image, it becomes strict and uniform within ± 5%. However, the value is not limited to this.

  If the electrostatic latent image is uniform, it can be seen that the correction of the average intensity was appropriate. If the size of the electrostatic latent image is not uniform, it will cause variation in the average intensity of the remaining light source. Therefore, the average intensity is repeatedly corrected until the size of the electrostatic latent image becomes uniform. Further, even if the average intensity is sufficiently corrected, if the electrostatic latent image is still not uniform, there is a possibility that the photoreceptor is non-uniform. In this case, it is possible to know the variation of the photosensitive member from the variation amount of the electrostatic latent image.

  As described above, after measuring the intensity of light emitted from each light source, the average intensity of the input signal to each light source is corrected, whereby a uniform electrostatic latent image can be obtained.

  In the present invention, the present invention is not limited to this, and ΔS / S (average) obtained by dividing ΔS by an average value may be used for evaluating the uniformity of an electrostatic latent image.

  Moreover, what is used as a reference for determining variations in the electrostatic latent image is not limited to the area of each electrostatic latent image, and may be the diameter or radius of a circle of the electrostatic latent image. In addition, the electrostatic latent image may be a rectangle, a square, or a trapezoid instead of a circle. In this case, the area or the length of one side may be used as a reference.

The vertical surface emitting laser has a problem that the output is not linear with respect to the input. When the average intensity I of the input signal is changed, the emitted light intensity does not change linearly. This is shown in FIG.
If the input and output are linear, it is a straight line as shown by a broken line in FIG. 7A, but actually deviates from this and becomes a curve shown by a solid line. Here, in the graph of FIG. 7, the horizontal axis is input and the vertical axis is output. The input is the intensity of the input signal, actually the injection current to the light source, and the output is the light intensity measured with an optical power meter.

  In addition, this curve is different for each light source. This is shown in FIG. In order to avoid complication, a graph is drawn for only five light sources (ch1 to ch5), but the number of light sources is not limited to this, and may be 20, 40, or more. As is apparent from this graph, even if the intensity correction described above is performed at one point on the horizontal axis (for example, i2), the other points (i1, i3) are displaced.

  In this embodiment, correction is performed at a plurality of locations for each intensity of the input signal. In the present embodiment, the above-described correction is performed on i1, i2, and i3 shown in FIG. In the present invention, the intensity of the input signal to be corrected is not limited to these three points, and more detailed correction is possible when performed at many points.

  The intensity of the input signal is i1, i2, and i3, respectively, as shown in FIG. FIG. 8 (a) looks similar to FIG. 1 (c). However, it is assumed that Δi in FIG. 8A is larger than ΔI in FIG.

  When correction is performed at each of the points i1, i2, and i3, an input signal as shown in FIG. 8B is obtained. Here, the value of ch3 is used as a reference. FIG. 9 shows this in the same manner as the table 31 in FIG. Such a table is a so-called lookup table. When performing the evaluation, the average intensity is set, and necessary values are read from this reference table. This is done via the PC as shown in FIG.

  Further, when the input value is not in the lookup table, for example, linear interpolation or the like is appropriately performed between i1 and i2 using the values of i1 and i2. This can be sufficiently performed by processing with a PC.

  When an electrostatic latent image is formed without correction, the sizes are not uniform as shown in FIG. On the other hand, as shown in FIG. 10B, if the correction is appropriate, the sizes of the electrostatic latent images are completely the same. However, it is assumed that the photoreceptor is completely uniform.

  In this embodiment, three input values i1 to i3 and five light sources ch1 to ch5 are drawn, but in the present invention, the number is not limited to these. In this embodiment, the electrostatic latent image is drawn as a circle. However, in the present invention, the shape is not limited to this, and may be an ellipse or a rectangle. Thus, by appropriately correcting the average intensity of the light source, the size, for example, area of the electrostatic latent image can be made uniform.

  Here, the evaluation of the areas of the plurality of electrostatic latent images is performed by obtaining an average value S (average) of the areas and its standard deviation ΔS and using these values. In this embodiment, the uniformity of the electrostatic latent image is evaluated using this ΔS. In this embodiment, a value representing this uniformity is obtained for each average intensity set in stages.

  For example, in each stage, if ΔS is ± 10% or less, it is assumed to be uniform. The value is not limited to this, and when pursuing high image quality, ΔS is a small value such as ± 5% or less. This allowable range and tolerance are appropriately allocated from the toner image on paper, which is the final output.

In this embodiment, the standard deviation ΔS is used for the evaluation of the area of the electrostatic latent image. However, the present invention is not limited to this, and ΔS / S (average) obtained by dividing the standard deviation by the average value is used. May be. Further, the electrostatic latent image may be a circle, and its diameter or radius may be used for the evaluation of uniformity.
In the present embodiment, the electrostatic latent image is drawn as a circle, but is not limited to this, and may be an ellipse, a rectangle, a square, a trapezoid, or the like. In the case of a square, rectangle, or trapezoid, the uniformity of the electrostatic latent image may be evaluated based on the length of one side.

The response waveform measuring means used in the present embodiment will be described with reference to FIG.
The vertical surface emitting laser 11 is driven by an input signal as shown in FIG. In this figure, it is pulsed light, but it may be continuous light.
Here, the optical system 12 is depicted as a single lens in order to avoid complexity, but in reality, it is a scanning optical system as shown in FIG.

The detector 13 is a photodiode (PD), and preferably has high sensitivity and high response speed. In order to measure in detail using pulsed light, the time resolution of the detector 13 is preferably several picoseconds (ps) to several nanoseconds (ns).
The display device 14 is an oscilloscope. The oscilloscope may be a general-purpose commercial product.

  In this embodiment, the detector 13 and the display device 14 cooperate to operate as intensity measuring means. The intensity measuring means may be an interface, a PC having control software, and a display device such as a liquid crystal display.

  The intensity measuring means is installed at a position equivalent to the electrostatic latent image forming position. However, in an actual image forming apparatus, if there is a photoconductor at the image forming position, the intensity measuring means cannot be installed. Therefore, the image forming apparatus is provided with a mechanical stage that allows the photoreceptor to escape when measuring the strength, and a mechanical stage that allows the strength measuring means to escape when the electrostatic latent image is formed on the photoreceptor. It has been.

  Assume that the input signal is a rectangular pulse wave as shown in FIG. The response waveform of this light has a blunt rise (100 in FIG. 11B) as shown in FIG. 11B (however, the degree of this bluntness depends on the intensity I of the input signal). This is one characteristic of the vertical surface emitting laser. Further, the unit of the optical response waveform intensity on the vertical axis in FIG. 11B is volts (V). At the rising edge 100, the desired intensity is not reached, and therefore the desired electrostatic latent image cannot be formed in the end. I is the average intensity.

  In this embodiment, a general-purpose optical power meter is used for measuring the intensity of light emitted from the light source. Although an optical output (W) can be obtained with an optical power meter, the output of pulsed light in the order of nanoseconds (ns) cannot be measured with the temporal resolution of the optical power meter. For this reason, when pulse light is used in power measurement, the optical power meter has a problem of insufficient time resolution. The light emission time of the pulsed light is, for example, several tens to several hundreds ns, and when it is desired to measure the peak intensity, a time resolution of several hundreds ps (picoseconds) to several ns is required.

  On the other hand, the photodiode (PD) used for the response waveform measuring means in this embodiment has a high time resolution. Therefore, the response waveform can be measured in detail even for pulsed light of about ns. However, the output of the PD is a voltage (V), and the power cannot be known. Therefore, in this embodiment, it is necessary to keep the average intensity uniform.

  In order to eliminate the dullness of the applied waveform in FIG. 11 (b), an input signal having a so-called overshoot with a high intensity at the head is used as shown in FIG. 12 (a). In the present invention, Iov is called peak intensity. If the intensity of Iov is appropriate, the response waveform approaches a rectangle as shown in FIG. However, if Iov is too strong, a response waveform with a rising top is obtained as shown in FIG. When Iov is weak, a response waveform as shown in FIG.

  The plurality of light sources in the vertical surface emitting laser have variations in light emission characteristics, and even if the same input signal, for example, FIG. 11A is input, the response waveform obtained is as shown in FIG. The rise 131 and the portion 132 corresponding to the average intensity vary. In FIG. 13, a response waveform graph is drawn with the falling edges 133 aligned. Here, depending on each correction described above, the portion 132 corresponding to the average intensity can be aligned (FIG. 13B). However, the variation of the rise 131 remains.

Therefore, as will be described next, correction is performed so that the variation in the rise is made uniform by setting the peak intensity to an appropriate value for each light source.
For a certain light source, the average intensity I of the input signal is constant, the overshoot Iov is variable, and the Iov having a desired response waveform is found. For example, as shown in FIG. 14A, the value of Iov is changed little by little (Iov0, Iov1, Iov2, Iov3), and their response waveforms are acquired (FIG. 14B). At this time, the response waveform is close to a rectangle when it is Iov2, and this value is the optimum Iov. This is performed for a plurality of light sources, and an appropriate Iov is obtained for each light source. Create lookup tables for these values. This is reflected in the input signal to cause each light source of the vertical surface emitting laser to emit light. This is shown in FIG. In order to avoid complication, the number of light sources is three here, but the present invention is not limited to this. As shown in FIG. 16B, appropriate peak intensities are different from ch1 to ch3, respectively, but the corrected response waveform is uniform as shown in FIG.

  Further, when the correction of the average intensity and the correction of the peak intensity are simultaneously performed on the light source, the two types of correction amounts are combined as shown in FIG. Although the average intensity I has been constant so far, if this greatly changes beyond the correction amount, the peak intensity needs to be further corrected. That is, the correction amount of the peak intensity obtained at a certain average intensity cannot be used at another average intensity. For this reason, the average intensity is changed stepwise to obtain the peak intensity correction amount.

  A description will be given of the evaluation of the electrostatic latent image with reference to FIG. Here, a square electrostatic latent image is formed. It is assumed that an image is formed from the left to the right (t0 to t1) in the figure using the scanning optical system. If the peak intensity is strong, the shape of the electrostatic latent image changes immediately after writing (immediately after t0).

  FIG. 21A shows an ideal case where a square electrostatic latent image is formed. FIG. 21B shows a case where the shape is slightly corrected but is slightly distorted. It is assumed that the area S and the width d of the electrostatic latent image are the same in (a) and (b). Therefore, in area and width, there is no difference between (a) and (b).

  Therefore, the height h of (a) and (b) is compared. Based on (a) as a reference, the uniformity of the electrostatic latent image is evaluated by how much (b) is deviated therefrom. The values to be evaluated are Δh = h (b) −h (a), the change rate is Δh / d, Δh / Δt, the angle θ, and the like. (Where Δt = t1−t0) Δh may be twice that of 2Δh. The smaller the variation in these values among the plurality of light sources, the more uniform the electrostatic latent image.

In FIG. 21A, consider forming an electrostatic latent image of h = 100 μm, d = 100 μm, and S = 10000 μm ² . In addition, Δt (= t1−t0) = 100 ns. In this case, Δh = 0, Δh / d = 0, Δh / Δt = 0, and θ = 0 °.

  In FIG. 21B, it is assumed that d = 100 μm and Δt = 100 ns are the same as FIG. 20A and h = 110 μm. Δh = 5 μm, Δh / d = 0.05, Δh / Δt = 0.05 (μm / ns), and θ = 5.71 °. If the peak intensity is appropriately corrected for each light source, Δh, Δh / d, Δh / Δt, and θ are all ideally zero.

  Δh, Δh / d, Δh / Δt, θ and average values and standard deviations thereof are obtained between a plurality of light sources, and the uniformity of the electrostatic latent image is evaluated. Δh (average), Δh (standard deviation), θ (average value), θ (standard deviation), and the like. Here, the standard deviation or a value obtained by dividing the standard deviation by the average value is obtained from the evaluation of the uniformity of the electrostatic latent image.

  In this embodiment, the uniformity is evaluated from the average value and standard deviation of Δh. If the electrostatic latent image is uniform in this evaluation, it can be understood that the correction of the peak intensity was appropriate. If the size and shape of the electrostatic latent image are not uniform, it will cause variations in the peak intensity of the remaining light source.

  Note that the allowable range and tolerance of these evaluation values are determined from the image quality evaluation of the toner image on the paper. If these tolerances are not satisfied, the peak intensity is repeatedly corrected until it is satisfied. The tolerance is, for example, a value of ± several% to ± 10%. In order to improve the image quality, it is determined to be ± 1% or less.

  In FIG. 21, the electrostatic latent image is drawn as a square or trapezoid for convenience. However, the actual electrostatic latent image spreads due to scattering of incident light in the layer of the photoconductor, spreads due to electric charge diffusion during electron transport of the photoconductor, and seems to have rounded corners. It becomes a shape.

  Even in the case where the desired shape of the electrostatic latent image to be formed is not rectangular, this occurs in image formation. For example, the writing is intentionally fattened (trapezoidal shape). In this case, the peak intensity needs to be excessively increased.

  In FIG. 14A, the peak intensity is changed stepwise, but the interval between the peak intensities is small. If this interval becomes large, the above peak intensity correction amount will not match. This is probably because the output is not linear with respect to the input. Therefore, it is necessary to change the peak intensity step by step at a certain large interval, and obtain the correction amount for each step.

  FIG. 19 shows the case where the peak intensity is changed in three stages. At each stage, a peak intensity correction amount is obtained. Although indicated by Δi in the figure, this is, for example, approximately the same as Δi shown in FIG.

  Consider forming a rectangular or trapezoidal electrostatic latent image. In FIG. 18, an electrostatic latent image is formed from left to right (t0 → t1) using the scanning optical system. When FIG. 19A is a rectangular electrostatic latent image and the peak intensity is small, the result is as shown in FIG. 19B, and when the peak intensity is increased, the results become (c) and (d) sequentially. 18 corresponds to FIG. 18, and step 1 in FIG. 18 corresponds to (a) in FIG. 19, steps 2 and 3 in FIG. 18 correspond to (c) and (d) in FIG. 19, respectively.

  In this case, a correction amount is obtained for each stepped peak intensity for each light source, and a reference table is created. As an example of the reference table, FIG. 20 shows a case where there are three light sources and three stages. The number of light sources and stages is not limited to three. In FIG. 20, the correction amount is Iov1-1. However, the present invention is not limited to this, and may be a set value on the control device or a ratio with respect to a reference.

  Values to be evaluated are Δh = h (b) −h (a), Δh / d, Δh / Δt, angle θ, etc. as the rate of change (where Δt = t1−t0). Further, instead of [Delta] h, 2 [Delta] h that is twice as much may be used. It can be said that the smaller the variation of these values among the plurality of light sources, the more uniform the electrostatic latent image. For the variation, the standard deviation of these evaluation quantities or the average value divided by the standard deviation is used. These values are obtained at each of the set peak intensity stages.

  The allowable range and tolerance of these evaluation values are determined from the image quality evaluation of the toner image on the paper. If these tolerances are not satisfied, the peak intensity is repeatedly corrected until it is satisfied. The tolerance is, for example, a value of ± several% to ± 10%. In order to improve the image quality, it is determined to be ± 1% or less.

  In a vertical surface emitting laser, for example, four light sources are used to irradiate a photosensitive member with light from them adjacent to each other by a polygon mirror to form one dot-like electrostatic latent image (vertical in FIG. 21). A long rectangle is a pattern. The scanning optical system will be described later.

  In the scanning optical system, a polygon mirror is used, which has a plurality of mirror surfaces (for example, six surfaces; FIG. 22C). The surface of the polygon mirror to be used can be designated for each light source by electrical control of the scanning optical system. For example, only one of the six mirrors is used (mirror surface 1. case 1 (FIG. 22A)) to form an electrostatic latent image, or two surfaces (mirror surfaces 1 and 2). Case 2 (FIG. 22B)), an electrostatic latent image may be formed. The four light sources are the light source 1, the light source 2, the light source 3, and the light source 4. In the former case, the light emitted from the light source 1 by the light source 4 is deflected by using the mirror surface 1. In the latter case, for example, the light emitted from the light source 1 and the light source 3 can be deflected by the mirror surface 1, and the light emitted from the light source 2 and the light source 4 can be deflected by the mirror surface 2.

  In either case, the same dot-like electrostatic latent image is to be formed. However, depending on the type of the photoconductor used, there may be a difference between the two electrostatic latent images. A phenomenon in which a difference occurs in the formed latent images even though the emission intensity (exposure energy density on the photoreceptor) is the same is called reciprocity failure.

  The use of the mirror surface is not limited to one surface and two surfaces, and may be more than this. In FIG. 22, a certain dot is drawn so as not to overlap with an adjacent dot, but may overlap partially. When the resolution of the image to be formed is high and the dots are large, adjacent dots partially overlap. The degree of overlap depends on the resolution and dot size. For example, at a resolution of 4800 dpi, the pitch is 5.29 μm, but when a dot-like electrostatic latent image having a diameter of 50 μm is formed, they are mostly overlapped. Naturally, this overlap affects reciprocity failure.

  In case 1, there is almost no time difference in light emission of the light sources 1 to 4, and in case 2, the light sources 1, 3 and the light sources 2, 4 are different because the mirror surfaces used are different. This slight time difference gives a time difference to charge transport in the charge transport layer of the photoreceptor, and also causes a difference in the electrostatic latent image due to the sensitivity characteristics of the photoreceptor. Specifically, the difference means that the size of the electrostatic latent image is different between case 1 and case 2. The areas are obtained for Case 1 and Case 2, and are designated S (a) and S (b), respectively. If there is a reciprocity failure, S (b)> S (a).

  Note that the present invention is not limited to using four light sources and two mirrors. More light sources and more mirror surfaces may be used. The value to be evaluated is not limited to the area of the electrostatic latent image, and may be a width. Further, since the difference depending on the mirror surface used is caused not only by the size of the electrostatic latent image but also by the magnitude of the potential, the magnitude of this potential may be measured.

  In addition, what is important in evaluating the electrostatic latent image described above is that there is no variation in light emission intensity among a plurality of light sources. This is because the size of the electrostatic latent image changes even if there is a variation in light emission. For this reason, it is necessary to eliminate as much as possible variations in light emission intensity between light sources such as average intensity and peak intensity by the above-described corrections.

  Even if there is a reciprocity failure and S (b)> S (a) as described above, the difference can be quantitatively determined, so that correction is possible. For example, if S (b) = 1.1 × S (a), an electrostatic latent image may be formed by increasing the average intensity by 10% in FIG. The value is not limited to this, and depends on the photoconductor used, the scanning method for forming an image, and the like. In this way, a correction amount for reciprocity failure based on the electrostatic latent image forming method can be obtained.

  As described above, when one dot-shaped electrostatic latent image is formed using four light sources, the writing position of each light source becomes a problem. That is, if the write positions of the four light sources are ideally aligned, the result is as shown in FIG. However, in reality, as shown in FIG. 23B, the writing position may be slightly shifted in each channel (exaggeratedly depicted).

  Of course, if the electric control is performed, the writing position can be finely adjusted. However, if there is such a positional shift, the latent image spreads as if blotting on the photoconductor, and the area and the like may not be required more accurately.

  In this embodiment, a belt-like electrostatic latent image is used instead of a dot-like electrostatic latent image. This is because, as shown in FIG. 23C, even if the writing position of each light source is slightly shifted, there is little influence on the height direction h, and the value to be evaluated is h. Further, in order to form such a belt-like electrostatic latent image using the scanning optical system, it is sufficient to use pulse input signals continuously as shown in FIG. The direction of formation of the electrostatic latent image is from left to right in the figure.

  Moreover, the reciprocity failure is dependent on the latent image pattern to be formed. For this reason, the degree of reciprocity failure is different and the correction amount is different between the dot-shaped pattern described above and the band-shaped pattern described below. Therefore, it is necessary to evaluate with different electrostatic latent image patterns.

  The use of the mirror surface is not limited to one surface and two surfaces, and may be more than this. In FIG. 22, a certain strip-shaped electrostatic latent image and an adjacent strip-shaped electrostatic latent image are drawn so as not to overlap each other, but may partially overlap each other. When the resolution of an image to be formed is high and the electrostatic latent image is large, adjacent belt-like electrostatic latent images partially overlap. The degree of overlap depends on the resolution and dot size. For example, at a resolution of 4800 dpi, the pitch is 5.29 μm, but when a strip-shaped electrostatic latent image having a height (width) of 50 μm is formed, they are mostly overlapped. Naturally, this overlap affects reciprocity failure.

  Also, FIGS. 24A and 24B show how the electrostatic latent image is formed when only one surface of the polygon mirror and two surfaces are used. When the photoreceptor has a reciprocity failure, the height h is h (b)> h (a). In this case as well, it is necessary to arrange the average intensity and peak intensity as much as possible among a plurality of light sources.

  Even if there is a reciprocity failure and h (b)> h (a) as described above, the difference is quantitatively understood, and therefore correction is possible. For example, assuming that h (b) = 1.1 × h (a), an electrostatic latent image may be formed by increasing the average intensity by 10% in FIG.

  In this manner, a reciprocity failure correction amount based on the electrostatic latent image forming method can be obtained. In addition, by using a strip-shaped electrostatic latent image, it is possible to evaluate a reciprocity failure with high accuracy and stability.

  FIG. 25 shows a scanning optical system using a vertical surface emitting laser. The scanning optical system includes a light source 131, a collimating lens 132, a cylindrical lens 133, a first mirror 134, a polygon mirror 135, a first scanning lens 136, a second scanning lens 137, and a second mirror 138. .

  This is merely an example, and in the present invention, the configuration and arrangement of the scanning optical system are not limited to this. The polygon mirror 135 rotates at a high speed of about 10,000 rpm to several tens of thousands rpm (rpm: round per minute) around the rotation axis 1351, and scans light incident on the polygon mirror. This scanning direction is called the main scanning direction. This is the longitudinal direction of the photoconductor 139. In addition, the photoconductor 139 rotates around the rotation shaft 1391. This direction is called the sub-scanning direction. The electrostatic latent image formed by light irradiation on the photoreceptor is, for example, 1392. Here, a state in which a belt-like electrostatic latent image is formed on the photosensitive member is drawn with exaggerated size and change width. The writing direction is indicated by an arrow in the figure.

Note that the photoconductor itself may not be included in the scanning optical system. Although not shown, an opening (aperture) is provided immediately before the light source 131.
The light source 131 is a vertical surface emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser). The wavelength λ is, for example, 780 nm.

<Image measuring device>
FIG. 26 schematically shows an image measuring apparatus 141 according to an embodiment of the present invention. The basic configuration of the image measuring apparatus 141 includes an electron gun 142, a condenser lens 143, a scanning lens 144, an objective lens 145, a light irradiation optical system 146, a sample 147 (photosensitive member), a sample stage 1450, an electron detector 1430, and a vacuum. A pump 149, an interface 148, and an electronic computer (computer and display) 1410. Reference numeral 1440 is an exaggerated enlargement of an electrostatic latent image of an arbitrary pattern formed by light irradiation on a charged photoconductor. The display of the electronic computer 1410 displays input information and an observed electrostatic latent image. This shows how data and image processing are performed on a computer.

Means for generating charged particles for charging the photoconductor 147 are specifically the electron gun 142 and the lenses 143, 144, and 145.
The means for irradiating the photoconductor with light is specifically a light irradiation optical system 146.
Means for observing an electrostatic latent image of an arbitrary pattern formed on the photosensitive member is specifically an electron gun 141, lenses 143, 144, 145 and an electron detector 1430.
The electron gun 142 may be used in, for example, a scanning electron microscope (SEM). The electron gun includes a hot filament, a field emission, etc. Any of them may be used.

  Considering charging the photoconductor with electrons using the electron gun 142, it is necessary to place the electron gun, photoconductor, etc. in a vacuum. This is not unique to the apparatus and is similar to the SEM. Therefore, the entire apparatus is evacuated using the vacuum pump 149. In FIG. 25, only one vacuum pump is drawn for convenience, but a rotary pump, a turbo molecular pump, an ion sputtering pump, or the like may be used in combination depending on the degree of vacuum to be achieved.

The charged particle is generally an electron having a negative polarity. However, ions may be used like an ion gun used in FIB (Focused Ion Beam). For example, an ion species such as Ga ⁺ .

  The condenser lens 143, the scanning lens 144, and the objective lens 145 are all magnetic field lenses or electrostatic lenses. A charged particle beam is scanned two-dimensionally on the sample 147 by the scanning lens 144. Here, the sample 147 is a photoconductor.

  Electrons are preferably used for charging the photoreceptor. When electrons are used, the charged potential on the surface of the photoreceptor varies mainly depending on the electron acceleration voltage and the irradiation time. The higher the electron acceleration voltage, the higher the charged potential on the surface of the photoreceptor. In the present invention, it is necessary to make the conditions equivalent to those for electrophotography. The conditions are that the acceleration voltage (Vacc) is about 1.0 to several kV, and the time is about several tens of seconds to several tens of minutes. When the charging potential is measured using, for example, a general-purpose surface potential meter, a value of about −600 to −1000 V is obtained. The charging potential is equivalent to that of an actual copying machine or printer.

  Instead of changing Vacc, the charging potential may be adjusted by applying a bias voltage to the photosensitive member.

  The light irradiation optical system 146 is a means for forming an electrostatic latent image having an arbitrary pattern by irradiating the photosensitive member with light. Specifically, the scanning optical system shown in FIG. In FIG. 26, the optical system 146 is inside the apparatus, but may be outside (in the atmosphere). In this case, in order to maintain the vacuum, the light from the scanning optical system may be guided to the photosensitive member by providing a transparent window such as glass with high transmittance in the apparatus.

  In FIG. 26, the sample photoconductor 147 is drawn as a flat plate (or a sheet), but it may be a cylinder (or a drum, 139 in FIG. 25). The sample stage 1450 can move three-dimensionally in x, y, and z.

  The principle of forming an electrostatic latent image on the photoreceptor is shown in FIG. The means for observing the electrostatic latent image preferably uses electrons. This uses the electron gun 142 used for charging. However, the current value needs to be weakened. For example, assuming that the current value at the time of charging is several nA, the current value at the time of observation is several pA, which is about one thousandth. This is to prevent the electrostatic latent image from disappearing due to electron irradiation. This is because the electrostatic latent image disappears faster as the electron beam having a higher current value is irradiated.

  The electron detector is a secondary electron detector. The observation electrons reach the photoconductor and cause secondary electrons to be emitted from the photoconductor. The principle that the electrostatic latent image can be measured is that secondary electrons are not emitted so much from the place where the electrostatic latent image is formed, and are well emitted from the place where the electrostatic latent image is not formed. Secondary electrons are detected by a secondary electron detector 147. The secondary electron detector includes a phosphor that emits light when irradiated with electrons, a light guide, a photomultiplier that multiplies the emitted light, and the like. This is a scanning type detector, but follows the scanning of the electron beam on the photosensitive member.

  Each of the above means is controlled by the computer 1410 via the interface 148. Detailed control of each means is performed by software in a computer.

  Here, it is assumed that the electrostatic latent image is formed (1440 in FIG. 26). The observed electrostatic latent image is output on a computer display and subjected to various data / image processing (1420 in FIG. 26). These can also be performed using general-purpose data / image processing software.

  There are cases where there are restrictions on the image evaluation apparatus. For example, the scanning range of the electron beam cannot be widened, or the size of the sample (photosensitive member) is limited. With respect to the scanning range of the electron beam, it is possible to scan a certain range (several mm × several mm) if a resolution of several nm is sacrificed as compared with a general-purpose SEM. However, many photoreceptors are several centimeters in diameter and several tens of centimeters in the longitudinal direction. It is difficult to scan the entire surface of the photoreceptor at once. Partial scanning is repeated by moving the photosensitive member. If a photoconductor of this size is used as a sample, the sample stage becomes large and the vacuum chamber needs to have a large capacity. Therefore, it is necessary to devise such as cutting out and measuring the photoconductor. In this case, scanning may be performed in a very narrow range.

  FIG. 28 shows the concept of the operation of the image evaluation apparatus according to the present embodiment. First, variations in average intensity and peak intensity are measured and corrected using a dedicated measuring means. Next, an electrostatic latent image is formed using the light source after the intensity correction. If the electrostatic latent image is uniform, it is determined that the intensity correction is appropriate. If it is not uniform, the intensity correction is performed again. The intensity correction is repeated until the electrostatic latent image becomes uniform. Assuming that the electrostatic latent image becomes uniform, a correction amount for the average intensity and a correction amount for the peak intensity are obtained. This is given as a lookup table. This is output 1.

  Next, the reciprocity failure is evaluated using a plurality of light sources in which both the average intensity and the peak intensity are appropriately corrected. The reciprocity failure depends on the type of the photoreceptor used first, and secondly depends on the scanning method when forming the electrostatic latent image. Specifically, one that uses only one surface of a polygon mirror, one that uses two surfaces, and one that uses more surfaces. The intensity correction amount can be obtained from the change in the size of the electrostatic latent image. This is output 2. This is also given as a lookup table.

  Output 1 and output 2 are recorded and stored as electronic information in an internal storage device of an electrophotographic apparatus such as a laser printer or a digital copying machine. The internal recording device is an electronic electric circuit or a hard disk. This electrophotographic apparatus uses the same (or equivalent) vertical surface emitting laser, scanning optical system, and photoconductor as those used in the evaluation. When forming an image, the electrophotographic apparatus always refers to the correction amount recorded and stored in the internal recording device and forms an electrostatic latent image with an optimum light emission intensity. Formation is possible. Therefore, the toner image on the paper to be finally output also becomes high quality.

DESCRIPTION OF SYMBOLS 11 Vertical surface emitting laser 12 Optical system 13 Intensity measuring means 32 Personal computer 33 Electric circuit 34 Vertical surface emitting laser 35 Scanning optical system 36 Intensity measuring means

JP 2007-240682 A

Claims (8)

A vertical surface emitting laser having a plurality of light sources arranged, driving means for emitting the vertical surface emitting laser with continuous light or pulsed light, and a laser beam emitted from the plurality of light sources is used to form an electrostatic latent image on the photosensitive member. An electrostatic latent image forming unit that forms an image, an average intensity and peak intensity correcting unit of the laser beam, and a variation in intensity of emitted light between a plurality of arranged light sources are measured at an electrostatic latent image forming position. Intensity measuring means, and electrostatic latent image measuring means for measuring the electrostatic latent image,
An image evaluation method for evaluating an electrostatic latent image formed on the photoconductor from a measurement result by the intensity measuring unit and the electrostatic latent image measuring unit,
Based on the variation in the intensity of the emitted light between the plurality of light sources measured by the intensity measuring means while continuously emitting the vertical surface emitting laser by the driving means, the correction means calculates the average intensity of the emitted light from each light source. Correct,
Next, a plurality of electrostatic latent images are formed on the photosensitive member while causing the vertical surface emitting laser to emit light with pulse light by the driving means, and the electrostatic latent image measuring means measures the electrostatic latent images. An image evaluation method characterized by evaluating the uniformity of the image.   The image evaluation method according to claim 1, wherein the correction of the average intensity of the emitted light can be performed in a plurality of stages according to the intensity of an input signal to the plurality of light sources. The image evaluation method according to claim 1 or 2, further measuring a response waveform of pulsed light for each of the plurality of light sources,
Correcting the peak intensity of the light source that needs to be corrected based on the measured response waveform;
An image evaluation method characterized by that.   The image evaluation method according to claim 3, wherein the correction of the peak intensity can be performed in a plurality of stages according to the intensity of an input signal to the plurality of light sources. The image evaluation method according to any one of claims 1 to 4, further comprising a deflecting reflecting surface having a plurality of reflecting surfaces,
Each forming an electrostatic latent image using a different number of reflective surfaces;
Measuring the shape of each electrostatic latent image formed using the different number of reflective surfaces;
Correcting the output of the light source that needs to be corrected based on the comparison result of the shape of the electrostatic latent image on each reflecting surface number;
An image evaluation method characterized by that.   When forming an electrostatic latent image, a pulse-shaped input signal is repeatedly supplied to the light source to form a strip-shaped electrostatic latent image that is long in the main scanning direction on the surface of the photosensitive member. The image evaluation method according to claim 5, wherein the electrostatic latent image is evaluated based on a length of the strip-shaped electrostatic latent image in a sub-scanning direction when the measurement is performed. An image evaluation apparatus that executes the image evaluation method according to claim 1,
A charged particle generator for generating charged particles for charging the photoreceptor;
A vertical surface emitting laser having a plurality of light sources;
An optical system provided on the optical path of the emitted light between the light source and the photosensitive member;
An outgoing light measuring unit for measuring the intensity of outgoing light from each light source after passing through the optical system;
An electrostatic latent image measuring unit for measuring the shape of the electrostatic latent image formed on the photoreceptor;
The output of the light source that needs to be corrected is corrected based on the intensity of the emitted light measured by the emitted light measuring unit and the shape of the electrostatic latent image measured by the electrostatic latent image measuring unit. A correction unit;
An image evaluation apparatus comprising:   An image forming apparatus including a photosensitive member on which an electrostatic latent image is formed by light emitted from a plurality of light sources, and an image evaluation device for evaluating the electrostatic latent image formed on the photosensitive member An image forming apparatus comprising the image evaluation apparatus according to claim 7.

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