JP2003114305A - Lens array, image forming device using the same, and inspecting method for the image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lens array capable of obtaining good image quality free from striped irregularities, and to provide an image forming device using the lens array. SOLUTION: The rod lens array satisfies such a condition 1 that an MTF part fluctuation as a difference between the mean value and the minimum value of a dot image contrast is within 18% in each section obtained by partitioning an image forming area where the dot image is formed by the lens array at a width of 10 mm. By satisfying the condition 1, such a factor is eliminated that the dot image with a drastic density difference is formed in each section of 10 mm. Then, in the case of printing with high recording density, the occurrence of striped irregularities on the whole printing surface is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a lens array for forming an image on a photosensitive surface by imaging light information from an array of point light sources that selectively emit light according to image information. The present invention relates to an image forming apparatus and an inspection method for the image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus which forms an image on a photosensitive drum or photographic paper by imaging light information emitted from an array of point light sources such as an LED array and a liquid crystal shutter array is generally used. A lens array in which a plurality of minute lenses are arranged is used. This lens array is a compound eye lens, and the entire image is formed by superimposing images formed by the lenses of the array in a limited range.

[0003]

However, in the electrophotographic image forming apparatus using the above-mentioned conventional lens array, streak-like unevenness may occur in the output image due to variation in optical characteristics of each lens of the lens array. . Such streak-like unevenness occurs when there is a portion with low resolution in the lens array. That is, the streak-like unevenness is caused not by the low absolute value of the resolution but by the large difference from the peripheral resolution. The width / spacing of the stripes that are easily recognized by the naked eye is approximately 0.5 to 10 mm, and it is particularly noticeable that such stripes occur in a cycle of about 1 to 5 mm.

Further, conventionally, the image quality formed by an image forming apparatus is evaluated by assembling the apparatus by combining a point light source array, a lens array and a photoconductor, and then the apparatus is actually operated to perform a photosensing and developing process. The unevenness of the formed image was evaluated. In this way, it is the actual situation that whether or not there is streak-like unevenness caused by the lens array cannot be grasped until the device is assembled. Therefore, as a result of the evaluation, when the image has streak-like unevenness and it is determined that the obtained image quality is poor, the device needs to be disassembled to identify the cause. That Cause such streaky unevenness occurs, whether in the lens array must be a factor analysis or whether there a point light source array. Further, when it is determined that the lens array is a defective product, it is necessary to reassemble the device by using a good product of the array. Therefore, the inspection process takes a lot of time and labor, and the productivity of the device is poor.

The present invention has been made in view of such a conventional problem, and an object thereof is to provide a lens array and an image forming apparatus using the same, which can obtain a good image quality without streaky unevenness. To do.

Another object of the present invention is to provide a lens array inspection method capable of evaluating streak-like unevenness caused by the lens array before assembling the apparatus and improving productivity. .

[0007]

In order to solve the above-mentioned problems, the invention according to claim 1 is used in an image forming apparatus having an array of point light sources which selectively emits light in accordance with image information. In a lens array for forming light information from a light source to form an image on a photosensitive surface, the array of point light sources has a width of approximately 42 μm over the entire effective width of the lens array.
When light is emitted by arranging at intervals, the difference between the average value and the minimum value of the contrast of the point image is almost equal in each section in which the image forming range where the lens array connects the point images is divided by a predetermined width. The gist is to satisfy the condition 1 that it is within 18%.

According to this configuration, by satisfying the condition 1, it is possible to eliminate the factor that a point image (dot) having a clear difference in shade is formed in each section divided into a predetermined width. Therefore, when printing is performed at a high recording density such as 1200 dpi, it is possible to prevent wide stripe unevenness from occurring on the entire printing surface. Note that the "point image contrast" here is defined as follows. That is, when the array-shaped point light sources are made to emit light in the above-mentioned light emission pattern, the maximum value of the light quantity of the n-th point image within the image forming range where the lens array connects the point images is Imax _- n, and the minimum value thereof is Imin. _- When n, n-th point image contrast (MTF - _n) is defined by the following equation.

MTF _- n = (Imax _- n-Imin _- n) / (Ima
x ₋ n + Imin ₋ n) × 100% The invention according to claim 2 is used in an image forming apparatus having an array of point light sources that selectively emits light according to image information, and forms optical information from the point light sources. In the lens array for forming an image on the photosensitive surface, the lens array forms a point image when the array of point light sources are arranged to emit light at intervals of approximately 42 μm over the entire effective width of the lens array. The gist is to satisfy the condition 2 in which the difference between the maximum value and the minimum value of the contrast of the point image is within approximately 30% within each section obtained by dividing the image forming range by a predetermined width.

According to this structure, by satisfying the condition 2, it is possible to eliminate the factor that a point image (dot) having a clear difference in gray level is formed in each section divided into a predetermined width. Therefore, when printing is performed at a high recording density such as 1200 dpi, it is possible to prevent wide stripe unevenness from occurring on the entire printing surface.

The invention according to claim 3 is used in an image forming apparatus having an array of point light sources which selectively emit light in accordance with image information, and which is selectively emitted in accordance with image information. In a lens array that forms an image on a photosensitive surface by imaging light information, when the array of point light sources are arranged to emit light at intervals of approximately 42 μm over the entire effective width of the lens array, the lens array It is said that the difference between the average value of the contrasts of the point images in each section in which the image forming range connecting the point images is divided by a predetermined width and the average value in the adjacent section is approximately 10% or less. The main point is to satisfy the condition 3.

According to this configuration, by satisfying the condition 3, it is possible to eliminate a factor that causes a difference in gray level between adjacent halftone dots, and it becomes difficult to generate streaks. Therefore, it is possible to avoid a phenomenon in which streaks are noticeable due to gradation.

The present invention according to claim 4 is used in an image forming apparatus having an array of point light sources that selectively emit light according to image information, and image information from the point light sources is formed into an image on a photosensitive surface. In a lens array for forming an image, when the array-shaped point light sources are arranged at approximately 42 μm intervals over the entire effective width of the lens array to emit light, the lens array forms the point image in the entire image forming range. The gist is to satisfy the condition 4 that the standard deviation of the contrast of the point image is within approximately 5%.

According to this structure, by satisfying the condition 4, it is possible to prevent the generation of fine stripe-shaped unevenness on the entire printing surface. Therefore, a good image quality without streaky unevenness can be obtained.

The invention according to claim 5 is used in an image forming apparatus having an array of point light sources which selectively emits light in accordance with image information, and images the light information from the point light sources to form an image on a photosensitive surface. In a lens array for forming an image, when the array-shaped point light sources are arranged at approximately 42 μm intervals over the entire effective width of the lens array to emit light, the lens array forms the point image in the entire image forming range. The gist is to satisfy the condition 5 that the standard deviation of the contrast of the point image is within approximately 12% with respect to the average value of the contrast in the entire image forming range.

According to this structure, by satisfying the condition 5, it is possible to prevent the generation of fine stripe-shaped unevenness on the entire printing surface. Therefore, a good image quality without streaky unevenness can be obtained.

According to a sixth aspect of the present invention, in the lens array according to any one of the first to fifth aspects, the lens array is a rod in which a plurality of gradient index rod lenses are arranged in one row or a plurality of rows. It is a lens array, and the gist is to satisfy the condition 6 in which the variation in the lens element diameter of each rod lens is approximately within the average lens element diameter ± 0.5%.

According to this structure, since the condition 6 is satisfied, when there is a variation in the lens element diameter of each rod lens which constitutes the gradient index rod lens array, a thin portion can be formed at a corresponding portion of the printing surface. It is possible to prevent streaky unevenness from occurring.

The invention according to claim 7 is the lens array according to any one of claims 1 to 6, wherein the lens array is a rod in which a plurality of gradient index rod lenses are arranged in one row or a plurality of rows. It is a lens array, and the variation of the meandering period length of each rod lens is almost the average period length ±
The gist is to satisfy the condition 7 that it is within 0.25%.

According to this structure, since the condition 7 is satisfied, when there is a variation in the meandering cycle length of each rod lens ray forming the gradient index rod lens array, a thin portion can be formed at a corresponding portion of the printing surface. It is possible to prevent streaky unevenness from occurring.

The invention according to claim 8 is the lens array according to any one of claims 1 to 7, wherein the lens array is a rod in which a plurality of gradient index rod lenses are arranged in one row or a plurality of rows. It is a lens array, and the gist is to satisfy the condition 8 that the lens element array parallelism is within P / TC.

According to this structure, since the condition 8 is satisfied, it is possible to prevent wide stripe unevenness from occurring due to the deviation of the optical axis angle between the gradient index rod lenses. Therefore, even when a rod lens array in which a large number of gradient index rod lenses are arranged is used as the lens array, good image quality without wide stripe-shaped unevenness can be obtained.
The “lens element array parallelism” mentioned here is the maximum value of the angle formed by the optical axes of the adjacent rod lenses.

The invention according to claim 9 is an image forming apparatus characterized by using the lens array according to any one of claims 1 to 8. According to this configuration, 12
When printing is performed at a high recording density such as 00 dpi, it is possible to form and output an image of good image quality without wide stripe-shaped unevenness or thin stripe-shaped unevenness.

According to a tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, a plurality of the lens arrays are provided, and images of a plurality of colors are superposed and formed by these lens arrays. , The angular variation of the optical axis between the lens arrays with respect to the lens array mounting reference plane is approximately ± 0.02 / TC (a value obtained by dividing 0.02 by the conjugate length TC of the lens array in mm units is radian). It is a gist to satisfy the condition 9 that the value is within the value).

According to this structure, the plurality of lens arrays are adjusted so as to satisfy the condition 9, and are mounted on the lens array mounting reference surface. As a result, the lens array having a large variation in the printing point position is adjusted in advance, and the variation in the angle between the lens surface of each lens array and the lens array mounting reference plane is approximately ± 0.02 / TC.
Within [mm] (unit: radian). For this reason, when performing multicolor printing using a plurality of lens arrays, it is possible to prevent the occurrence of streaky unevenness due to color misregistration.

The invention according to claim 11 is used in an image forming apparatus having an array of point light sources which selectively emits light in accordance with image information. The light information from the point light sources is formed into an image on a photosensitive surface. an inspection method for an image forming apparatus for forming the the lens array and a light receiving portion and the array of point light sources arranged in a position conjugate with the array of point sources effective width of the lens array The point light source and the lens array are moved in the lens arrangement direction of the lens array with respect to the light receiving section so as to emit light in a uniform light emitting pattern over the entire area, and the amount of light of each point image formed by the lens array is received. Part, the contrast of all the point images in the image forming range is obtained, and the average of the contrast of the point images in each section in which the image forming range is divided by a predetermined width based on the detection result of the light receiving section. value The difference between the minimum value is summarized in that to determine whether or not within a predetermined value.

According to this structure, the judgment result that the difference in each of the sections is within the predetermined value is obtained, so that the good image quality without the streak-like unevenness caused by the lens array is obtained. Can be performed before assembling the device. That is, the streak-like unevenness due to the lens array can be evaluated before the device is assembled. Therefore, the inspection process itself of the device after the assembling can be simplified, and the defect of the lens array itself can be grasped before the assembling of the device, so that the productivity of the device is improved.

The invention according to claim 12 is used in an image forming apparatus having an array of point light sources which selectively emits light in accordance with image information. The light information from the point light sources is formed into an image on a photosensitive surface. an inspection method for an image forming apparatus for forming the the lens array and a light receiving portion and the array of point light sources arranged in a position conjugate with the array of point sources effective width of the lens array The point light source and the lens array are moved in the lens arrangement direction of the lens array with respect to the light receiving section so as to emit light in a uniform light emitting pattern over the entire area, and the amount of light of each point image formed by the lens array is received. Section, and obtain the contrast of all the point images in the image forming range based on the detection result by the light receiving unit, and determine the maximum contrast of the point image in each section in which the image forming range is divided by a predetermined width. Difference between the value and the minimum value is summarized in that to determine whether or not within a predetermined value.

According to this structure, the judgment result that the difference in each of the sections is within the predetermined value is obtained, so that the good image quality without the streak-like unevenness caused by the lens array can be obtained. Can be performed before assembling the device. Therefore, the inspection process itself of the device after the assembling can be simplified, and the defect of the lens array itself can be grasped before the assembling of the device, so that the productivity of the device is improved.

The thirteenth aspect of the present invention is used in an image forming apparatus having an array of point light sources that selectively emits light in accordance with image information, and forms optical information from the point light sources to form an image on a photosensitive surface. an inspection method for an image forming apparatus for forming the the lens array and a light receiving portion and the array of point light sources arranged in a position conjugate with the array of point sources effective width of the lens array The point light source and the lens array are moved in the lens arrangement direction of the lens array with respect to the light receiving section so as to emit light in a uniform light emitting pattern over the entire area, and the amount of light of each point image formed by the lens array is received. Section, the contrast of all the point images in the image forming range is obtained, and the average of the contrast of the point images in each section obtained by dividing the image forming range by a predetermined width based on the detection result by the light receiving section. When the difference between the average value in the adjacent section is summarized in that to determine whether or not within a predetermined value.

According to this structure, since the determination result that the difference is within the predetermined value is obtained, the evaluation that the good image quality without the streak-like unevenness caused by the lens array can be obtained before the device is assembled. It can be carried out. For this reason,
Since the inspection process itself of the device after assembling can be simplified and the defect of the lens array itself can be grasped before the assembling of the device, the productivity of the device is improved.

The invention according to claim 14 relates to claims 11 to 1.
4. The image forming apparatus inspection method according to any one of 3 above, wherein the light emission pattern is obtained by arranging the array of point light sources at substantially equal intervals over the entire effective width of the lens array to emit light. That is the summary. According to this configuration, it is effective to inspect an image forming apparatus having a high recording density specification such as 1200 dpi.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a rod lens array embodying the present invention, an optical printer as an image forming apparatus using the same, and an inspection method for the optical printer will be described below with reference to the drawings.

First, each embodiment of the rod lens array and the optical printer using the same will be described. [First Embodiment] FIG. 7 shows an optical printer using the rod lens array according to the first embodiment, and FIG. 8 shows an LED print head used in the optical printer. Same L
The rod lens array according to the first embodiment is used for the ED print head. Further, FIG. 9 shows the rod lens array according to the first embodiment and the imaging action by the array.

The optical printer 11 shown in FIG. 7 has a cylindrical photosensitive drum 12, an LED print head 13, and a charger 1.
4, a developing device 15, a transfer device 16, a fixing device 17, an erasing lamp 18, a cleaning device 19, a cassette 20, a stacker 21, and the like. On the surface of the photosensitive drum 12, that is, the photosensitive surface,
For example, a photoconductive material (photoreceptor) such as amorphous Si is made. The photosensitive drum 12 is rotating at the printing speed. The photosensitive surface of the rotating photosensitive drum 12 is uniformly charged by the charger 14. And L
The ED print head 13 irradiates the light (dot image) of the dot image to be printed on the photosensitive surface of the photosensitive drum 12 to neutralize the charge where the light hits. Then, the developing device 15
Apply toner onto the photosensitive surface according to the charged state on the photosensitive surface. Then, the transfer device 16 transfers the toner onto the sheet 22 sent from the cassette 20. Paper 2
The second sheet is fixed by being heated by the fixing device 17, and is sent to the stacker 21. On the other hand, the photosensitive drum 1 after transfer is completed
In No. 2, the erase lamp 18 neutralizes the charge over the entire surface, and the cleaning device 19 removes the remaining toner.

L used in such an optical printer 11
As shown in FIG. 8, the ED print head 13 has an LED array 23 as an array point light source that selectively emits light according to image information and a rod lens array 24 as an erecting equal-magnification image forming lens array. It has and.

The LED array 23 is constructed by mounting an LED array chip and an IC driver chip on a substrate. The LED array 23 is turned on and off for each array element according to print information (image information) such as a serial signal. Then, the light emitted from each array element that has been turned on (light emitted from the object plane in FIG. 9) is formed by each rod lens 25 of the rod lens array 24, and an image composed of a large number of point images is formed on the photosensitive drum 12. Is formed on the photosensitive surface (image surface of FIG. 9). The image thus formed is a whole image in which images formed by connecting the rod lenses 25 of the rod lens array 24 in a limited range are superimposed. The array pitch of the array elements of the LED array 23 (light emitting point pitch)
Is 21 μm for a recording density of 1200 dpi (24 lp / mm), the point image pitch is also 1200 dpi.
In the case of, it becomes 21 μm.

As shown in FIGS. 8 and 9, the rod lens array 24 includes a plurality of gradient index rod lenses 25 having a gradient index distribution in the radial direction in two rows between two frames 26, 26. It is arranged. In order to obtain a good image quality without streaky unevenness in the optical printer 11 using such a large number of small gradient index rod lenses 25, L
It is desirable that the lens performance be constant over the entire image forming range while adjusting the light emission amount of the ED array 23 and arranging the arrays 23 and 24 with high accuracy.

The rod lens array 24 includes a large number of gradient index rod lenses (hereinafter simply referred to as rod lenses) 2.
Since 5 are arranged and arranged, the optical performance thereof changes periodically. Since the variation occurs evenly over the entire image forming range, it does not always cause deterioration in image quality depending on the cycle and amplitude. However, if a partial variation occurs due to the performance variation of each rod lens 25 forming the rod lens array 24, the partial variation occurs particularly in an image forming apparatus such as a high resolution printer having a recording density of 600 dpi or more. Streaky unevenness (image shading unevenness) occurs due to the fluctuation. Therefore, in a high resolution printer of 600 dpi or more, the rod lens array 2 that does not cause such partial variation
4 must be used.

Therefore, the rod lens array 24 according to the first embodiment is made to satisfy the condition 1 out of the following conditions 1-9. The numerical values (evaluation item values) shown under the following conditions are set for the 1200 dpi specification rod lens array 24 used for the 1200 dpi specification LED array 23.

(Condition 1) Each section (10 mm) in which the image forming range is divided by an arbitrary predetermined width (for example, about 10 mm)
Within a section), the MTF partial variation, which is the difference between the average value and the minimum value of the contrast of the point image, is within about 18%.

(Condition 2) The difference between the maximum value and the minimum value of the contrast of the point image in each section (5 mm section) in which the image forming range is divided by an arbitrary predetermined width (for example, about 5 mm). MTF max-min should be within 30%.

(Condition 3) The average value of the contrast of the point image in each section (1 mm section) in which the image forming range is divided by an arbitrary predetermined width (for example, about 1 mm) and the adjacent section (1 mm section) The MTF section average difference, which is the difference with the same average value within, should be within 10%.

(Condition 4) The standard deviation of the contrast of the point image in the entire image forming range is within 5%.
For example, the contrast of the point image is 50%, 45%, 48
%, 52%, 55%, the standard deviation of the contrast of the point image is 3.81%.

(Condition 5) The standard deviation of the contrast of the point image in the entire image forming range should be within 12% of the average value of the contrast of the point image in the entire image forming range. For example, when the average value is 50% and the standard deviation is 5%, 5/50 = 0.1 is expressed as 10%.

(Condition 6) The variation in the lens element diameter of each rod lens 25 constituting the rod lens array 24 should be within the average lens element diameter ± 0.5%. In addition,
The “lens element diameter” mentioned here means each rod lens 25.
Is the effective diameter d.

(Condition 7) The variation of the meandering cycle length (pitch) of the rod lenses 25 is approximately the average cycle length ± 0.2.
Must be within 5%. (Condition 8) The array pitch of each array element of the LED array 23 actually used for the LED print head 13 is P, L
The distance between the ED array 23 and the photosensitive drum 12 is the conjugate length TC.
Then, the parallelism of the lens element arrangement should be within P / TC. The “lens element array parallelism” mentioned here is the maximum value of the angles formed by the optical axes of the adjacent rod lenses 25.

(Condition 9) The angle variation of the optical axis between the rod lens arrays 24 with respect to the lens array mounting reference plane to which the outer surface of the frame 26 of each rod lens array 24 is fixed is approximately ± 0.02 / TC [mm] ( Unit: radians) In addition, "0.02 /
“TC [mm] (unit: radian)” represents a value obtained by dividing 0.02 by a value representing the conjugate length TC of the lens array in mm unit and representing it in radian unit).

The "point image contrast" in each of the above conditions 1 to 9 is obtained by the following measuring method, for example. In this measuring method, first, as shown in FIG. 1, an array of point light sources (for example, an LED array) 23A is arranged at a predetermined position. That is, with respect to the rod lens array 24, the point light source 23 is located at a position conjugate with one slit 30.
Place A. Behind this slit 30, the light receiving element 3
1 is set. The slit 30 and the light receiving element 31 form a light receiving portion. Point light source 23A used here
The size of the light emitting points is 15 × 15 μm, the interval between the light emitting points is approximately 42 μm (the array pitch of each array element is approximately 21 μm).
m, which corresponds to the interval when every other 1200-dpi LED array 23 is turned on). By turning on all the light emitting points of the point light source 23A, it is possible to obtain a light emission pattern when the array of point light sources are arranged at intervals of approximately 42 μm over the entire effective width of the lens array to emit light.

In this way, the point light source 23A and the rod lens array 2 are operated with the array of point light source 23A emitting light.
4 is moved in the lens arrangement direction of the lens array 24 (direction shown by the arrow in FIG. 1). Thereby, the light receiving elements 31 sequentially detect the light amounts of all the point images formed by the rod lens array 24 on the slit 30. The amount of light detected here corresponds to the amount of light of all point images in the image forming range that the rod lens array 24 connects to the photosensitive surface of the photosensitive drum 12. The “image forming range” referred to here is a range for one line of an image formed on the photosensitive surface of the photosensitive drum 12. This image forming range is determined by the effective width of the rod lens array 24.

In this way, the light quantity of each point image in the image forming range is detected. The maximum value of the light quantity of the n-th point image in the range is Imax _- n, and the minimum value thereof is Imin _- n. The contrast (MTF _- n) of the point image is defined by (Equation 1) below.

MTF−n = (Imax ₋ n−Imin ₋ n) / (Imax ₋ n + Imin ₋ n) × 100% (Equation 1) The “point image contrast” thus defined is within the image forming range. For all point images in. In this way, the contrast distribution of all the point images connected by the rod lens array 24, which is one element expressing the resolving power of the electrophotographic optical printer 11, that is, each point in the image forming range defined as described above. Image contrast (MT
Find the distribution of F).

FIGS. 3 and 4 are graphs prepared for rod lens arrays as comparative examples with respect to the first embodiment. FIG. 3 shows the distribution of the contrast (MTF) of the point image in the image forming range, and FIG. 4 shows the partial variation of MTF under the above condition 1.

According to the first embodiment described above, the following operational effects are exhibited. (A) In the rod lens array of the comparative example, as can be seen from the distribution of the point image contrast (MTF) shown in FIG.
Regarding the contrast value itself, it cannot be seen that there is a clear difference from the surroundings over the entire image forming range. However, the MTF partial variation of this rod lens array is shown in FIG.
As shown in, 1 in the 10mm section other than around 95mm
Although it is sufficiently smaller than 8%, it is 18.6% in one 10 mm section around 95 mm. Actually 1 using the rod lens array of this comparative example
When printing was performed with the optical printer 11 of 200 dpi specification, wide streak unevenness was generated in the vicinity of 95 mm corresponding to the 10 mm section in which the MTF partial variation was 18.6%.
When a printed matter was observed, there was a difference in dot size (amount of adhered toner) at the corresponding position from that of the peripheral portion at the location where such a wide stripe-shaped unevenness occurs. 1200 dpi
As a result of performing a printing test with the optical printer 11 having the specifications, in the rod lens array in which the MTF partial variation exceeds 18.6% in any 10 mm section as in the above comparative example, the width at the position corresponding to the section is widened. Wide streak-like unevenness occurred.

On the other hand, an optical printer 1 of 1200 dpi specification is actually used by using the rod lens array 24 of this example.
When printing was performed with No. 1, wide streak unevenness did not occur on the entire printing surface. This is because when the condition 1 is satisfied, the MTF within the entire 10 mm section of the entire image forming range.
Partial fluctuation is within 18%, whichever narrow section (10
This is because it is possible to eliminate the factor of forming a point image (dot) having a clear gray level difference even in the mm section). Therefore, according to the rod lens array 24 according to the first embodiment, when printing is performed at a high recording density of 1200 dpi, it is possible to obtain a good image quality without wide stripe unevenness on the entire printing surface.

(B) According to the optical printer 11 using the rod lens array 24 according to the first embodiment, 1200d
When printing is performed at a high recording density of the pi specification, it is possible to form and output an image having good image quality with no wide stripe-shaped unevenness.

Second Embodiment The rod lens array 24 according to the second embodiment is made to satisfy the above condition 2.

According to the second embodiment, the following operational effects are exhibited. (C) FIG. 5 is a graph prepared for a rod lens array as a comparative example with respect to this embodiment.
The TF part max-min is shown. As shown in the figure, the MTF portion max-min of the rod lens array 24 is 9
Within one narrow section (5 mm section) near 5 mm, it is 31.1% and exceeds 30%. When I actually printed with the 1200 dpi optical printer 11 using this rod lens array, the MTF max-min was 3
Wide streak-like unevenness was generated in the vicinity of 95 mm corresponding to the 5 mm section where the ratio was 1.1%. In addition, as a result of performing a printing test with a 1200 dpi optical printer 11 on several rod lens arrays created while changing the performance of the rod lenses, it was found that the MTF within any 5 mm section.
When the partial max-min exceeds 30%, wide stripe-shaped unevenness occurs at the position corresponding to the section.

On the other hand, when the rod lens array 24 of the present embodiment was used to actually print with the 1200 dpi optical printer 11, wide streak-like unevenness did not occur. This is because by satisfying the condition 2, it is possible to eliminate the factor that a point image (dot) with a clear gray level difference is formed in a narrow section (5 mm). Therefore, according to the rod lens array 24 according to the second embodiment,
When printing is performed at a high recording density of 200 dpi, it is possible to obtain good image quality without wide stripe-shaped unevenness on the entire printing surface.

(D) According to the optical printer 11 using the rod lens array 24 according to the second embodiment, 1200d
When printing is performed at a recording density of pi, it is possible to form and output an image with good image quality without wide stripe-shaped unevenness or thin stripe-shaped unevenness.

Third Embodiment The rod lens array 24 according to the third embodiment is made so as to satisfy the above condition 3.

According to the third embodiment, the following operational effects are obtained. (E) FIG. 6 is a graph prepared for a rod lens array as a comparative example with respect to the present embodiment, and shows the MTF section average difference of Condition 3 above. As shown in the figure, the average difference in MTF section of this rod lens array is 275 mm.
Within one narrow section (1 mm section) in the vicinity, 10.
3%, and less than 10% in other sections. When actually printing with the optical printer 11 of 1200 dpi using this rod lens array, the MTF interval average difference is 275 which corresponds to a 1 mm interval of 10.3%.
Thin streak-like irregularities occurred around mm. This thin streak-like unevenness is caused because the difference in shade between adjacent halftone dots becomes large and halftone dots for gradation expression cannot be formed as intended.

On the other hand, in the rod lens array 24 of this example, as a result of the printing test, no thin streak-like unevenness was found on the entire printing surface. This is because by satisfying the condition 3, it is possible to eliminate the factor that the difference in gray level between adjacent halftone dots becomes large, and it becomes difficult to generate streaks. Therefore, it is possible to avoid a phenomenon in which streaks are noticeable due to gradation. In other words, since the halftone dots for gradation expression can be formed as intended, it is possible to prevent the occurrence of streak-like unevenness, particularly thin streak-like unevenness, which occurs due to the fact that the halftone dots cannot be formed as intended.
Therefore, the rod lens array 2 according to the third embodiment
According to No. 4, when printing is performed at a high recording density of 1200 dpi, it is possible to obtain a good image quality without streak unevenness, particularly fine streak unevenness on the entire printing surface. In particular, it is possible to avoid a phenomenon in which streaks are noticeable due to gradation.

(F) In addition, according to the optical printer 11 using the rod lens array 24 according to the third embodiment, 12
When printing is performed at a high recording density of 00 dpi, it is possible to form and output an image of good image quality without streaky unevenness, particularly fine streak unevenness.

[Fourth Embodiment] The rod lens array 24 according to the fourth embodiment is made so as to satisfy the above condition 4.

According to the fourth embodiment, the following operational effects can be obtained. (G) Rod lens array 2 of this example satisfying condition 4 above
4, the average value of the contrast of the point image in the entire image forming range is 44.2% (see FIG. 3), and the standard deviation of the contrast of the point image in the entire image forming range is 4.6.
It was 7%. A printing test was conducted using several rod lens arrays prepared in the same manner as above. As a result, when the standard deviation of the contrast of the point image in the entire image forming range exceeds 5%, thin streak-like unevenness became conspicuous on the entire printing surface. On the other hand, when the standard deviation is within 5% as in the rod lens array 24 of this example, thin streak-like unevenness does not occur on the entire printing surface. Therefore, the rod lens array 24 according to the fourth embodiment.
According to this, when printing is performed at a high recording density of 1200 dpi, it is possible to obtain a good image quality without fine stripe-shaped unevenness on the entire printing surface.

(H) According to the optical printer 11 using the rod lens array 24 according to the fourth embodiment, 1200d
When printing is performed at a high recording density of pi, it is possible to form and output an image of good image quality without thin streaky unevenness on the entire printing surface.

[Fifth Embodiment] The rod lens array 24 according to the fifth embodiment is made so as to satisfy the above condition 5. That is, the rod lens array 2 according to this example
4, the average value of the contrast of the point image in the entire image forming range is 44.2% (see FIG. 3), and the standard deviation of the contrast of the point image in the entire image forming range is 4.6.
It was 7%. At this time, 4.67 / 44.2≈0.1
(Approximately 10%). Therefore, the rod lens array 24 according to the present example satisfies the above condition 5.

According to the fifth embodiment, the following operational effects are obtained. (I) A printing test was conducted using several rod lens arrays. As a result, even if the standard deviation itself is small,
When the average value becomes small and the standard deviation exceeds 12% with respect to the average value, thin streak-like unevenness becomes conspicuous on the entire printing surface. On the other hand, in the rod lens array 24 of this example, since the above Condition 5 is satisfied,
No thin streak-like unevenness was formed on the entire printed surface. Therefore, according to the rod lens array 24 according to the fifth embodiment, when printing is performed at a high recording density of 1200 dpi,
It is possible to obtain good image quality without fine stripe-shaped unevenness on the entire printing surface.

(E) According to the optical printer 11 using the rod lens array 24 according to the fifth embodiment, 1200d
When printing is performed at a high pi recording density, it is possible to form and output an image of good image quality without thin stripe unevenness.

[Sixth Embodiment] Next, a rod lens array 24 according to a sixth embodiment will be described. In the present embodiment, the rod lens array 2 according to the first embodiment described above.
Similar to 4, the rod lens array 24 in which a large number of small gradient index rod lenses are arranged is used as the lens array, and the rod lens array 24 is made so as to satisfy the above condition 6.

The rod lens array according to the sixth embodiment has the following operational effects. (L) In the rod lens array 24 created by mixing rod lenses in which the variation in the lens element diameter of each rod lens exceeds ± 0.5% with respect to the average lens element diameter, the rod lens array 24 is provided at a position corresponding to the rod lens. A section (1 mm section) in which the MTF section average difference shown in FIG. 6 exceeds 10% is formed. As a result of a printing test using this rod lens array, thin streak-like irregularities were generated at the corresponding positions on the printing surface. On the other hand, since the rod lens array 24 of this example satisfies the condition 6, each rod lens 2 constituting the gradient index rod lens array 24 is
When there is a variation in the lens element diameter of No. 5, it is possible to prevent the generation of thin streaky unevenness at a corresponding portion of the printing surface.

(2) According to the optical printer 11 using the rod lens array 24 according to the sixth embodiment, 1200d
When printing is performed at a high pi recording density, it is possible to form and output an image of good image quality without thin stripe unevenness.

[Seventh Embodiment] Next, a rod lens array 24 according to a seventh embodiment will be described. In this embodiment, as in the sixth embodiment, the gradient index rod lens array 24 is used, and the array 24 is made to satisfy the above condition 7.

Rod lens array 2 according to the seventh embodiment
According to 4, the following operational effects are exhibited. (W) In the rod lens array 24 created by mixing rod lenses in which the variation of the meandering period of the light rays of the rod lens 25 exceeds the average period length ± 0.25%, the position corresponding to the rod lens is shown in FIG. A section (1 mm section) in which the MTF section average difference shown exceeds 10% is formed. As a result of a printing test using this rod lens array, thin streak-like irregularities were generated at the corresponding positions on the printing surface. On the other hand, the rod lens array 24 of this example
Since Condition 7 is satisfied, each rod lens 25
When there is a variation in the meandering period length of the light, the average difference of the MTF section is within 10%, and it is possible to prevent the generation of fine stripe-shaped unevenness at the corresponding portion of the printing surface.

(F) According to the optical printer 11 using the rod lens array 24 according to the seventh embodiment, 1200d
When printing is performed at a high pi recording density, it is possible to form and output an image of good image quality without thin stripe unevenness.

[Eighth Embodiment] Next, a rod lens array 24 according to an eighth embodiment will be described. In this embodiment, as in the sixth embodiment, the gradient index rod lens array 24 is used, and the array 24 is made to satisfy the above condition 8.

A wide streak causes 1 MTF partial fluctuation.
When a rod lens array with an MTF max-min of more than 8% and a MTF max-min of more than 30% is examined, the optical axis of each of the constituent rod lenses is about 0.002 (radian) with respect to the adjacent rod lens at the corresponding position. Was making an angle. This rod lens array is designed so that the distance between the light source (object plane) and the image plane (see FIG. 9), that is, the conjugate length TC is about 10 mm, and this optical axis angle deviation is about 20 μm on the image plane. There will be a gap. This is 12
It is almost equal to the light emitting point pitch of the LED array of the 00 dpi specification. When the LED array was changed to 600 dpi and checked, the allowable optical axis angle deviation was 1200 dpi.
It was approximately equal to 0.0045 (radian), which was about twice the deviation in the case of the LED array of the specifications. From this, it was found that when the array pitch of the array elements of the LED array to be actually assembled is P, the lens element array parallelism must be maximum P / TC (radian).

Rod lens array 2 according to the eighth embodiment
According to 4, the following operational effects are exhibited. (Yo) Since Condition 8 is satisfied, each rod lens 25
It is possible to prevent wide stripe unevenness from occurring due to the deviation of the optical axis angle between them. Therefore, the rod lens array 24
As a result, even when a large number of gradient index rod lenses are arranged, good image quality without wide stripe unevenness can be obtained.

(T) According to the optical printer 11 using the rod lens array 24 according to the eighth embodiment, 1200d
When printing is performed at a high recording density of pi, it is possible to form and output an image of good image quality with no wide stripe-shaped unevenness.

[Ninth Embodiment] Next, an optical printer 11 according to a ninth embodiment will be described. This optical printer 1
1 is capable of outputting a color image.

In order to obtain a color image with an image forming apparatus such as an optical printer, an image of three or more colors such as yellow,
The magenta, cyan, and black images are superimposed and formed on the photosensitive surface of the photosensitive drum 12. Therefore, in the optical printer 11, it is necessary to arrange a plurality (three or more) of the LED print heads 13 shown in FIG. 8 in which the LED array 23 and the rod lens array 24 are assembled.
In this case, if the images of the respective colors cannot be correctly superimposed, streak-like color unevenness will occur due to color misregistration.
Such streak-like color unevenness is caused by each rod lens array 24.
It occurs when there is a deviation in the image forming position of the point image formed by. That is, since each image point is formed at a pitch of about 21 μm in an optical printer of 1200 dpi specification, if the image forming position of the point image deviates by a pitch equal to or more than this pitch, the intended color cannot be reproduced and the streak pattern cannot be reproduced. The color will be uneven. In addition, 600
With a dpi printer, the deviation amount of the image forming position is almost 42
It must be within μm.

As described above, when multicolor printing is performed by combining a plurality of LED print heads 13 each having the same rod lens array 24 as in each of the above-described embodiments, a good image quality can be obtained with a single color and there is no problem. Unevenness may occur. As a result of studying this color unevenness, it was found that the image forming positions of the point images of the respective colors are shifted by about 20 μm, although the point image size (dot size) varies little. As a result of investigating the corresponding part of the rod lens array 24, the lens surface of the rod lens 25 is 9 with respect to the lens array mounting reference plane of the rod lens array 24.
Where it should be 0 degrees, approximately ± 0.02 / TC [mm]
(Unit: radian) It was found that there was a deviation. Due to this angle deviation, the optical axis of the rod lens 25 is tilted,
As a result of calculation taking into account that the incident light from the D array 23 is refracted on the lens surface of the rod lens 25, the angle deviation is almost the same as the position deviation of the point image (deviation of the image forming position). From this, the variation in the angle between the lens surface of the rod lens 25 and the lens array mounting reference surface is approximately ±.
It has been found that it must be within 0.02 / TC [mm] (unit: radian).

Therefore, in the optical printer 11 according to the present example,
Similar to the rod lens array 24 of each of the above-described embodiments, a plurality (three or more) of rod lens arrays 24 that can obtain good image quality without streaky unevenness are provided. The angular variation of the optical axis of each rod lens array 24 with respect to the lens array mounting reference plane to which the outer surface of the frame 26 of each rod lens array 24 is fixed is approximately ± 0.02 / TC [m
m] (unit: radian).

The optical printer 11 according to the ninth embodiment has the following operational effects. (R) The plurality of rod lens arrays 24 are adjusted so as to satisfy the condition 9, and are assembled on the lens array mounting reference plane. As a result, the rod lens array having a large variation in the printing point position is adjusted in advance, and the variation in the angle between the frame 26 of each rod lens array and the lens array mounting reference plane is approximately ± 0.02 / TC.
Within [mm] (unit: radian). For this reason, when performing multicolor printing using a plurality of lens arrays, it is possible to prevent the occurrence of streaky unevenness due to color misregistration.

[Inspection Method of Optical Printer 11] Next, each embodiment of the inspection method of the optical printer 11 will be described with reference to FIGS. 1 and 2.

[First Embodiment of Inspection Method] This inspection method includes the following steps 1 to 5. (Step 1) The above-mentioned array of point light sources 23A is arranged at a predetermined position. That is, with respect to the rod lens array 24, the array-shaped point light source 23A is arranged at a position conjugate with one slit 30, and the light receiving element 31 is arranged behind the slit 30 (see FIG. 1).

(Step 2) Array-shaped point light source (light emitting point size is 15 × 15 μm, light emitting point interval is approximately 42 μm)
By lighting all the light emitting points of 23A, light is emitted in a uniform light emitting pattern over the entire effective width of the rod lens array 24.

(Step 3) The array-shaped point light source 23A and the rod lens array 24 are moved with respect to the slit 30 in the lens arrangement direction of the lens array 24 (the direction of the arrow in FIG. 1) to connect the rod lens array 24. The light receiving element 31 detects the light amount of each point image.

(Step 4) The contrasts of all point images in the image forming range are obtained. The "point image contrast" here is obtained by the above (formula 1). (Step 5) Is the MTF partial variation, which is the difference between the average value and the minimum value Imin of the contrast of the point images, within approximately 18% within each section (10 mm section) in which the image forming range is divided by a predetermined width? Determine whether or not.

The inspection method of the optical printer 11 according to the first embodiment has the following operational effects. (So) In the above step 5, it is possible to obtain the determination result that the MTF partial variation in each section is within approximately 18%,
The evaluation that a good image quality without streak-like unevenness due to the rod lens array 24 can be obtained can be performed before the device is assembled. That is, the streak-like unevenness caused by the rod lens array 24 can be evaluated before the device is assembled. In other words, the performance of the rod lens array 24 itself can be evaluated without actually performing a printing test. Therefore, it is possible to simplify the inspection process itself of the device after assembling, and it is possible to grasp the defect of the rod lens array 24 itself before assembling the device. Therefore, the rod lens array 2
The streak-like unevenness caused by No. 4 can be evaluated before the device is assembled, and the productivity can be improved.

[Second Embodiment of Inspection Method] The inspection method of the optical printer 11 according to the second embodiment is the same as the steps 1 to 3 in the inspection method of the optical printer 11 according to the first embodiment.
Only the step 5 of 5 is changed. That is, the inspection method according to this example includes the above steps 1 to 4 and the following step 6.

(Step 6) MTF part max-mi which is the difference between the maximum value Imax and the minimum value Imin of the point image contrast within each section (5 mm section) in which the image forming range is divided by a predetermined width.
It is determined whether n is within about 30%.

According to the optical printer inspection method of the second embodiment, the following operational effects are obtained. (T) In step 6 above, the MTF part ma within each 5 mm section
Since the determination result that x-min is within about 30% is obtained, it is possible to perform an evaluation that good image quality without streak-like unevenness caused by the rod lens array 24 can be obtained before the device is assembled. Therefore, the streak-like unevenness caused by the rod lens array 24 can be evaluated before the device is assembled, and the productivity can be improved.

[Third Embodiment of Inspection Method] The inspection method of the optical printer 11 according to the third embodiment is the same as steps 1 to 5 in the inspection method of the optical printer 11 according to the first embodiment.
Of these, only step 5 is changed. That is,
The inspection method according to this example includes steps 1 to 4 and step 7 described below.
Includes and.

(Step 7) M, which is the difference between the average value of the contrast of the point image in each section (1 mm section) in which the image forming range is divided by a predetermined width, and the average value in the adjacent section.
It is determined whether or not the TF section average difference is within approximately 10%.

According to the inspection method of the optical printer 11 of the third embodiment, the following operational effects can be obtained. (D) In step 7, the determination result that the MTF section average difference within each 1 mm section is within 10% is obtained, and thus good image quality without streak-like unevenness caused by the rod lens array 24 is obtained. It can be evaluated that the device can be installed before the device is assembled. Therefore, the rod lens array 2
Evaluation of streak-like unevenness due to 4 before assembling the apparatus [Modification] The present invention can be modified and embodied as follows.

In each of the above-mentioned embodiments, the rod lens array 24 in which a plurality of rod lenses 25 having a refractive index distribution in the radial direction are arranged in two rows is used, but the number of rows is one or three or more. May be.

In each of the above embodiments, the rod lens array 24 is used as the erecting equal-magnification image forming lens array, but the present invention is not limited to this. The erecting equal-magnification image forming lens array may be of any type as long as it can form the erecting equal-magnification image formation on the photosensitive surface of the photosensitive drum 12 by forming optical information of the light emitted from each array element of the LED array 23. . For example, the erecting equal-magnification imaging lens array may be a normal erecting equal-magnification imaging optical lens or a plurality of gradient index flat plate microlenses arranged in one or more rows.

In each of the above embodiments, the array-shaped point light source is composed of the LED array 23, but the present invention is not limited to this structure. The array-shaped point light source to which the present invention can be applied may be one that can generate and extinguish light for each element, or one that can transmit and block light from an external light source for each pixel. For example, the array of point light sources may be configured by an external light source such as a discharge tube and an optical shutter array such as a liquid crystal shutter array that transmits / blocks light from the light source for each pixel according to image information. .

In each of the above embodiments, the optical printer 11
Uses an LED print head 13 having an LED array 23 and a rod lens array 24, but the present invention is not limited to this. For example, the optical printer 11 may be a liquid crystal shutter printer using an optical writing head including the liquid crystal shutter array and the rod lens array 24 or another lens array for equal-magnification imaging.

In each of the above-described embodiments, an example in which the present invention is applied to an optical printer is shown, but the present invention can be applied to other than the optical printer. For example, the LED print head 13
The present invention can be applied to a copying machine using an optical writing head such as the above, a multifunction machine having a printer function, a printing function, and a fax function.

In the rod lens array 24 according to each of the above-described embodiments, the numerical values (evaluation item values) shown in the above conditions 1 to 9 are compared with the rod lens array 24 of 1200 dpi specification used for the LED array 23 of 1200 dpi specification. However, the present invention is not limited to this. 60
For the rod lens array 24 used in the LED array 23 suitable for printing with a recording density of 0 dpi or higher, the numerical values (evaluation item values) shown in the above respective conditions 1 to 9
Are set to different values.

In the optical printer 11 according to the ninth embodiment, images of a plurality of colors are superposed and formed on the photosensitive surface, but the present invention is not limited to this. For example, the present invention can be applied to an optical printer in which images of respective colors are formed on four photosensitive drums and these are superposed.

The rod lens array 24 according to the first embodiment satisfies the condition 1, but the same lens array 2 is used.
4 may satisfy condition 1 and condition 4 or 5. The rod lens array 24 according to the second embodiment satisfies the condition 2, but the lens array 24 may satisfy the condition 2 and the condition 4 or 5.

The rod lens array 24 according to the third embodiment satisfies the condition 3, but the same lens array 2 is used.
The condition 4 may satisfy the condition 3 and the condition 4 or 5. It goes without saying that the present invention can be applied to the rod lens array 24 that satisfies all the conditions 1 to 5.

The rod lens array 24 according to the sixth embodiment satisfies the condition 6, but the same lens array 2 is used.
4 may satisfy the conditions 6 and 7 or 8, or the conditions 6, 7 and 8.

In the optical printer inspection method according to the first embodiment, it is determined whether Condition 1 is satisfied, but it is determined whether Condition 1 and Condition 4 or 5 are satisfied. You may

In the optical printer inspection method according to the second embodiment, it is determined whether Condition 2 is satisfied, but it is determined whether Condition 2 and Condition 4 or 5 are satisfied. You may

In the inspection method for the optical printer according to the third embodiment, it is determined whether or not the condition 3 is satisfied, but it is determined whether or not the condition 3 and the condition 4 or 5 are satisfied. You may

In each of the above embodiments, the array of point light sources are arranged at intervals of approximately 42 μm over the entire effective width of the lens array to obtain a light emission pattern, but the present invention is not limited to this. Not limited.

The technical idea that can be understood from the above-described embodiments will be described below. (1) In the lens array according to claim 1, the predetermined width is approximately 10 mm.

(2) In the lens array according to claim 2, the predetermined width is approximately 5 mm. (3) In the lens array according to claim 3, the predetermined width is approximately 1 mm.

(4) A lens used in an image forming apparatus having an array of point light sources that selectively emits light according to image information, and forms an image on a photosensitive surface by imaging light information from the point light sources. In the array, when the array-shaped point light sources are arranged to emit light by arranging at intervals of approximately 42 μm over the entire effective width of the lens array, the light amount of the n-th point image in the image forming range where the lens array forms point images. The maximum value of
Imax _- n, the minimum value I min _- When the _- (n MTF) is defined by the following equation, MTF _- n-th point image contrast as _{n n = (Imax - n-} Imin - n) / (Imax - n + Imin _-
n) × 100% M which is a difference between the average value and the minimum value of the contrast in each section obtained by dividing the image forming range by an arbitrary predetermined width.
A lens array satisfying the condition 1 in which the TF partial variation is approximately within 18%.

(5) A lens used in an image forming apparatus having an array of point light sources that selectively emits light according to image information, and forms an image on a photosensitive surface by imaging light information from the point light sources. In the array, when the array-shaped point light sources are arranged to emit light by arranging at intervals of approximately 42 μm over the entire effective width of the lens array, the light amount of the n-th point image in the image forming range where the lens array forms point images. The maximum value of
Imax _- n, the minimum value Imin _- if the _- (n MTF) is defined by the following equation, MTF _- n-th point image contrast as _{n n = (Imax - n-} Imin - n) / (Imax - n + Imin -
n) × 100% The condition that the MTF part max-min, which is the difference between the maximum value and the minimum value of the contrast in each section obtained by dividing the image forming range by an arbitrary predetermined width, is within about 30%. A lens array satisfying 2.

(6) A lens used in an image forming apparatus having an array of point light sources that selectively emits light in accordance with image information, and forms an image on a photosensitive surface by imaging light information from the point light sources. In the array, when the array-shaped point light sources are arranged to emit light by arranging at intervals of approximately 42 μm over the entire effective width of the lens array, the light amount of the n-th point image in the image forming range where the lens array forms point images. The maximum value of
Imax _- n, the minimum value Imin _- if the _- (n MTF) is defined by the following equation, MTF _- n-th point image contrast as _{n n = (Imax - n-} Imin - n) / (Imax - n + Imin -
n) × 100% The MTF section average difference, which is the difference between the average value of the contrast in each section obtained by dividing the image forming range by an arbitrary predetermined width and the average value in the adjacent section, is approximately 10 A lens array satisfying condition 3 of being within%.

[0117]

As described above, claims 1, 2, and
According to the inventions 3, 4, and 5, it is possible to obtain a good image quality without streaky unevenness.

According to the sixth, seventh and eighth aspects of the present invention, even when a rod lens array in which a large number of gradient index rod lenses are arranged is used as the lens array, good image quality without streaky unevenness can be obtained. it can.

According to the ninth aspect of the present invention, when printing is performed at a high recording density, it is possible to form and output an image of good image quality without wide stripe unevenness or thin stripe unevenness.

According to the tenth aspect of the present invention, when multicolor printing is performed using a plurality of lens arrays, it is possible to prevent streaky unevenness due to color misregistration. According to the eleventh, twelfth and thirteenth aspects of the present invention, it is possible to evaluate the streak-like unevenness due to the lens array before assembling the apparatus, and it is possible to improve the productivity.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a method for measuring a point image contrast (MTF).

FIG. 2 is a graph showing the detected light amount of each point image detected by the measuring method of FIG.

FIG. 3 is a graph showing a distribution of contrast (MTF) in the rod lens array according to the first embodiment.

FIG. 4 is a graph showing a partial variation in MTF used for explaining the rod lens array according to the first embodiment.

FIG. 5 is a graph showing an MTF part max-min used for explaining the rod lens array according to the second embodiment.

FIG. 6 is a graph showing an MTF section average difference used to describe a rod lens array according to a third embodiment.

FIG. 7 is a schematic configuration diagram showing an optical printer using the rod lens array according to the first embodiment.

FIG. 8 is a schematic configuration diagram showing an LED print head used in the optical printer.

FIG. 9 is an explanatory diagram showing a rod lens array according to the first embodiment and an image forming action thereof.

[Explanation of symbols]

11 ... Optical printer as image forming apparatus, 12 ... Photosensitive drum, 13 ... LED print head, 23 ... LED array as array point light source, 24 ... Rod lens array, 25 ... Rod lens.

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) G02B 27/18 H04N 1/036 F Term (Reference) 2C162 AE28 AE40 AE47 AF84 FA04 FA17 FA45 5C051 AA02 CA08 DB02 DB22 DB29 DC04 DE33

Claims (14)

[Claims] 1. A lens array used in an image forming apparatus having an array of point light sources that selectively emits light in accordance with image information and forms an image on a photosensitive surface by imaging light information from the point light sources. In the above, when the array-shaped point light sources are arranged to emit light by being arranged at an interval of approximately 42 μm over the entire effective width of the lens array, each section is defined by a predetermined width within an image forming range where the lens array forms point images. A lens array satisfying the condition 1 in which the difference between the average value and the minimum value of the point image contrasts is within about 18%. 2. A lens array used in an image forming apparatus having an array of point light sources that selectively emits light in accordance with image information and forms an image on a photosensitive surface by imaging light information from the point light sources. In the above, when the array-shaped point light sources are arranged to emit light by being arranged at an interval of approximately 42 μm over the entire effective width of the lens array, each section is defined by a predetermined width within an image forming range where the lens array forms point images. A lens array satisfying condition 2 in which the difference between the maximum value and the minimum value of the point image contrast is within about 30%. 3. An array which emits light selectively according to image information. An image forming apparatus having an array of point light sources which selectively emits light according to image information is used to form an image of light information from the point light source. In the lens array for forming an image on the photosensitive surface by the array of points, when the array of point light sources are arranged to emit light at intervals of approximately 42 μm over the entire effective width of the lens array, the lens array forms a point image. Satisfying the condition 3 that the difference between the average value of the contrast of the point image in each section obtained by dividing the formation range by a predetermined width and the average value in the adjacent section is approximately 10% or less. Characteristic lens array. 4. A lens array used in an image forming apparatus having an array of point light sources that selectively emits light according to image information, and forms an image on a photosensitive surface by imaging light information from the point light sources. The standard of the contrast of the point image in the entire image forming range where the lens array forms point images when the array point light sources are arranged to emit light at intervals of about 42 μm over the entire effective width of the lens array. A lens array satisfying condition 4, wherein the deviation is within approximately 5%. 5. A lens array used in an image forming apparatus having an array of point light sources that selectively emits light according to image information, and forms an image on a photosensitive surface by imaging light information from the point light sources. The standard of the contrast of the point image in the entire image forming range where the lens array forms point images when the array point light sources are arranged to emit light at intervals of about 42 μm over the entire effective width of the lens array. A lens array, wherein the deviation satisfies Condition 5 that the deviation is within approximately 12% with respect to the average value of the contrast in the entire image forming range. 6. The lens array is a rod lens array in which a large number of gradient index rod lenses are arranged in one row or a plurality of rows, and the variation in lens element diameter of each rod lens is approximately the average lens element diameter ± 0. The lens array according to any one of claims 1 to 5, which satisfies Condition 6 of being within 5%. 7. The lens array is a rod lens array in which a large number of gradient index rod lenses are arranged in one row or a plurality of rows, and variations in the meandering cycle length of each rod lens are approximately the average cycle length ± 0. The lens array according to any one of claims 1 to 6, which satisfies Condition 7 of being within 25%. 8. The lens array is a rod lens array in which a large number of gradient index rod lenses are arranged in one row or a plurality of rows, and the condition 8 that the lens element array parallelism is within P / TC is satisfied. Claim 1 characterized by the above-mentioned.
The lens array according to any one of items 1 to 7. 9. An image forming apparatus using the lens array according to claim 1. Description: 10. A plurality of the lens arrays are provided, and the lens arrays are configured to form images of a plurality of colors in an overlapping manner, and the angle variation of the optical axis between the lens arrays with respect to the lens array mounting reference plane. Is approximately ± 0.02 / TC (lens array conjugate length TC is mm
The image forming apparatus according to claim 9, wherein the condition 9 is within a value obtained by dividing 0.02 by a unit value in a radian unit. 11. An image forming apparatus used for an image forming apparatus having an array of point light sources that selectively emits light according to image information, and forms an image on a photosensitive surface by imaging light information from the point light sources. an inspection method, the relative lens array and a light receiving portion and the array of point light sources arranged in a position conjugate with uniform emitting the array of point sources across the effective width throughout the lens array Light is emitted in a pattern, the point light source and the lens array are moved in the lens array direction of the lens array with respect to the light receiving unit, and the light amount of each point image formed by the lens array is detected by the light receiving unit, The contrast of all the point images in the image forming range is obtained, and the difference between the average value and the minimum value of the contrast of the point image in each section obtained by dividing the image forming range by a predetermined width based on the detection result by the light receiving unit. But Inspection method of an image forming apparatus characterized by determining whether it is within definite. 12. An image forming apparatus used for an image forming apparatus having an array of point light sources that selectively emits light in accordance with image information, and forms an image on a photosensitive surface by imaging light information from the point light sources. an inspection method, the relative lens array and a light receiving portion and the array of point light sources arranged in a position conjugate with uniform emitting the array of point sources across the effective width throughout the lens array Light is emitted in a pattern, the point light source and the lens array are moved in the lens array direction of the lens array with respect to the light receiving unit, and the light amount of each point image formed by the lens array is detected by the light receiving unit, Obtaining the contrast of all point images in the image forming range based on the detection result by the light receiving unit, in each section of the image forming range divided by a predetermined width,
A method for inspecting an image forming apparatus, comprising: determining whether a difference between the maximum value and the minimum value of the contrast of the point image is within a predetermined value. 13. An image forming apparatus used in an image forming apparatus having an array of point light sources that selectively emits light according to image information, and forms an image on a photosensitive surface by imaging light information from the point light sources. an inspection method, the relative lens array and a light receiving portion and the array of point light sources arranged in a position conjugate with uniform emitting the array of point sources across the effective width throughout the lens array Light is emitted in a pattern, the point light source and the lens array are moved in the lens array direction of the lens array with respect to the light receiving unit, and the light amount of each point image formed by the lens array is detected by the light receiving unit, Obtaining the contrast of all point images in the image forming range, based on the detection result by the light receiving unit, the average value of the contrast of the point image in each section dividing the image forming range by a predetermined width, and the adjacent section Inspection method of an image forming apparatus the difference between the average value in the and judging whether within a predetermined value. 14. The light emitting pattern according to claim 11, wherein the array of point light sources are arranged at substantially equal intervals over the entire effective width of the lens array to emit light. The method for inspecting an image forming apparatus according to claim 1.