• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    PURPOSE: To provide an image forming device that can ensure uniformity of a resolution in the lens arrangement direction while maintaining a high basic resolution thereby making an uneven gray scale inconspicuous even in the case of processing half-tone. CONSTITUTION: An object face 14 is placed to be opposed to a one lens end face of a rod lens array 10 and an image face 16 is placed to be opposed to the other lens end face and the operating distance of the object side and that of the image side are selected optically nearly equal to each other. An actual distance TC0 between the object face and the image face is limited between a conjugate length TC1 maximizing the average value MTFave of an MTF (modulation transfer function) of the rod lens array single body in the lens arrangement direction and a conjugate length TC2 minimizing ΔMTF (=(MTFmax-MTFmin)/MTFave) and the offset ΔTC (=!TC0-TC1!) with respect to the conjugate length TC1 maximizing the MTFave is selected within a range of 0 mm<ΔTC<+0.2 mm.
    公开号:KR20020005458A
    申请号:KR1020010040195
    申请日:2001-07-06
    公开日:2002-01-17
    发明作者:오기슈야；이키코이치로；토야마미노루
    申请人:이주하라 요죠우；닛뽄 시트 글래스 가부시끼가이샤；
    IPC主号:
    专利说明:

    Image Forming Apparatus
    [12] The present invention relates to an image forming apparatus using a rod lens array. In particular, the present invention relates to an image forming apparatus having a basic resolution by arranging an image plane and an object plane at an appropriate position while ensuring uniform resolution. This technique is very useful when applied to contact image sensors or LED printers.
    [13] As shown in Fig. 1, the rod lens array 10 is constituted by a unit enlarged image optical system, in which a plurality of rod lenses 12 each having a shrinkage index distribution in the radial direction are arranged such that their optical axes are parallel to each other. Is arranged to be. Unit Enlarged Image Optical systems are widely used in facsimile machines, copiers, scanners, and LED printers. The object plane 14 is arranged at the opposite end face of the rod lens 12, and the image plane 16 is arranged opposite the other end thereof. In an image reading system such as the contact image sensor shown in FIG. 2, the object plane 14 is the original document surface and the image plane 16 is the sensor pixel retaining surface. In an image recording system such as an LED printer, the object plane is the light emitting surface of the LED component and the image plane is the drum surface.
    [14] In the design of the optical position of these image forming apparatuses, it is essential to set the mean value MTFave of the Modulation Transfer Function (MTF) to the largest possible value. The mean value MTFave is an average value of the MTFs calculated in the lens array direction (= horizontal direction of the rod lens array). After all, MTF represents the basic resolution of a rod lens array. As a result, the object plane 14 and the image plane 16 are positioned to satisfy at least the following conditions: The lens moving distance Lo on the object side (= distance from one lens end face to the object plane) is the image side. It is optically equal to the lens shift distance Lo on (= distance from other lens end face to image plane). Another method often used is to adjust the distance TC between the object plane and the image plane (called object-image distance TC) to maximize the mean MTFave of the MTF.
    [15] MTF is given by the following equation:
    [16] MTF (%) = [(imax-imin) / (imax-imin)] x 100
    [17] In the above equation, the terms imax and imin are obtained in the following way. As shown in FIG. 3, the rod lens array 10 accepts a square grid pattern (= original image) 20 and forms an image 22 of the pattern. The sensor receives the image 22. The relative maximum imax and relative minimum imin of the amount of light in the received image 22 are measured. Evaluating when the MTF approximates 100%, the image formed by the optical system approximates the optical image (the resolution of the optical system is large) more accurately.
    [18] Actual measurements are made using an optical system as shown in FIG. 4. In the figure, light emitted from a light source 30 such as a halogen lamp passes through the filter 31, the diffuser plate 32, and the rectangular test chart 33. As a result, a rectangular lattice pattern is formed. The rod lens array 10 forms an image of a rectangular grid pattern. CCD image sensor 34 accepts an image and converts it into a corresponding electrical signal. The rod lens array 10 moves in the direction of the concentric arrow. Through the movement of the rod lens array, the image is illuminated throughout its length. The waveform of the output signal of the CCD image sensor 34 is output to the data processor 35. The data processor 35 properly processes the output waveforms to have a relative minimum imin and a relative maximum imax of the waveform, and uses them to calculate the MTF. The MTF average calculated in the lens array direction is the MTFave of the lens array.
    [19] In addition to the work to adjust the object-image distance (TC) to minimize the mean (MTFave) of the MTF, here is another study. For example, in an image reading system, if there is a platen glass where the original document can limit the positional deviation in only one direction, the optimal focus position on the object surface side will be the platen glass to increase the correct depth of focus. Deviation from the surface. In another study, an image recording system may use a non-focus positional relationship to mitigate the adverse effects of variations in light emission of LED elements.
    [20] In rod lenses, the resolution is distributed in the radial direction in the field of view. Thus, the image superimposed by the rod lens array can be either the lens radius (when the sensor pixel / LED element is aligned with the center position of the lens array) or the lens diameter (when the sensor pixel / LED element is not aligned with the center position of the lens array). Some cycles of) include a sharp change in resolution in the transverse direction. If a road lens array on the market uses 600 dip resolution or more, variations in resolution cannot be detected.
    [21] Recent trends in high resolutions have prevented the prior art from guaranteeing uniformity of resolution while retaining its fundamental resolution. In dealing with halftone images used in image reading / writing systems, nonuniformities in optical density often occur.
    [22] Accordingly, an object of the present invention is to provide an image forming apparatus that guarantees uniform resolution in the direction of a lens array, and can reduce the non-uniformity of optical density even when handling halftone images while retaining fundamental resolution. have.
    [23] According to the present invention, the image forming apparatus uses a unit magnified image rod lens array including a plurality of rod lenses each having a reflection index distribution in the radial direction, and their optical axes are arranged to be arranged parallel to each other, and the object plane is It is arranged on the opposite end face of the rod lens array, the image plane is arranged opposite to its other end face, and the lens working distance of the rod lens array on the object side is practically the same as on the image side. The image forming apparatus has a combined distance TC1 and ΔMTF (= (MTFmax-MTFmin) / MTFave) in which the actual object-image distance Tco is the minimum value of the MTF of the rod lens array in the direction of the lens array. Is set between the compound distances TC2 where the distance is minimized, or the actual object-image distance Tco becomes equal to the compound distance TC2 when ΔMTF is minimum and the displacement amount ΔTC (= | TCo-TC1 | )) Is set within 0 mm <ΔTC <+0.2 mm with respect to the compound distance TC1 at which the MTFave is maximized. In the image forming apparatus, the object-image distance Tco is more preferably set to +0.05 mm < DELTA TC <+ 0.15 mm.
    [24] The inventors of the present invention studied this phenomenon when halftone images were used at high resolution and found that the nonuniformity of optical density could not be detected and came to the following conclusion. Through research, we found that: 1) it is convenient to use the new variable ΔMTF to assess optical density nonuniformity, and 2) generally, the mean value of MTF in the lens array direction (horizontal direction) ( It was found that the compound distance TC1 of MTFave is maximized and the compound distance TC2 at which ΔMTF is minimized is not the same.
    [25] As described above, in the present invention, the composite object distance TC1 and ΔMTF (= (MTFmax) in which the actual object-image distance Tco is the minimum value of the mean value MTFave of the MTF of the rod lens array in the direction of the lens array. -MTFmin) / MTFave) is set between the compound distances TC2 that are minimized, or the actual object-image distance Tco becomes equal to the compound distance TC2 when ΔMTF is minimum and the displacement amount ΔTC ( = | TCo-TC1 |) is set within 0 mm <ΔTC <+0.2 mm with respect to the compound distance TC1 at which the MTFave is maximized. In the image forming apparatus, it is more preferable to set the object-image distance Tco sms +0.05 mm <ΔTC <+0.15 mm. The composite distance TC2 of △ MTF is minimized and the composite distance TC1 at MTFave is minimized, and the rod lens and the like (direction: the + direction is to increase the compound distance and-direction is to decrease the compound distance) It is determined by the refractive index distribution of. Therefore, in the present invention, the actual object-image distance TCo is the composite distance TC1 in which the mean value MTFave of the MTF of the rod lens array is maximized in the direction of the lens array and the composite distance TC2 in which ΔMTF is minimized. It is important to be set in between. Further, in the present invention, the lens operating distance of the rod lens array to the object side is substantially the same as that of the image side. Therefore, the optical deviation amount on each object side and image side is ΔTC / 2. For this reason, the decrease of the mean value MTFave of the MTF is within the allowable range. Unevenness of resolution in the lens array direction is ensured while retaining high resolution. Thus, the nonuniformity of optical density can be ignored even when dealing with halftone images.
    [26] This description is related to the subject matter contained in Japanese Patent Application No. 2000-207380 (filed Jul. 7, 2000) and is incorporated herein by reference in its entirety.
    [1] 1 is an exemplary diagram illustrating an image forming apparatus using a rod lens array.
    [2] 2 is an exemplary diagram illustrating a contact image sensor.
    [3] 3 is an exemplary diagram illustrating an MTF.
    [4] 4 is an exemplary diagram illustrating an optical system for measuring MTF.
    [5] 5 is a graph showing simulation results of one example of a rod lens array.
    [6] 6 is a graph showing actual measurement results of a rod lens array.
    [7] 7 is a graph showing actual measurement results of different rod lens arrays.
    [8] <Explanation of symbols for the main parts of the drawings>
    [9] 10: rod lens array 12: rod lens
    [10] 14: object plane 16: image plane
    [11] 20: square grid pattern 22: image
    [27] The MTF of the rod lens array having the design specification given below is calculated in the transverse direction (lens element arrangement direction) in ascending order of the refractive index distribution coefficient. The calculation result is shown in FIG. In the calculation, a 24 lp / mm (lp / mm = line pair / mm) pattern was used, and MTFave and ΔMTF were calculated on the object-image distance TC. The design criteria for a basic rod lens array are:
    [28] Rod lens diameter (D): 0.563 mm
    [29] Composite length providing maximum MTFave (TC1): 9.9 mm
    [30] Rod lens length (Zo): 4.34 mm
    [31] Opening angle (maximum tilt angle) (Θo): 20 °
    [32] The refractive index distribution of the rod lens is given by
    [33] n (r) 2 = n o 2 · {1- (g · r) 2 + h 4 (g · r) 4 + h 6 (g · r) 6 + h 8 (g · r) 8}
    [34] Where r is the distance measured in the radial direction from the optical axis of the rod lens
    [35] no: Refractive index on optical axis of rod lens (= 1.625)
    [36] g: Refractive index distribution coefficient (= 0.8423)
    [37] h4, h6, h8: ascending refractive index distribution coefficient
    [38] In FIG. 5, the ascending refractive index distribution coefficients from A to D are shown in Table 1.
    [39] Table 1
    [40] If h4 h6 h8
    [41] A 1.50 -25 175
    [42] B 1.50 -27 200
    [43] C 1.50 -22 200
    [44] D 1.40 -25 200
    [45] 5, in any one of cases A to D, the composite distance TC1 at the mean value MTFave of the MTF of the rod lens array in the lens array direction is minimized, and ΔMTF (ΔMTF = (MTFmax−MTFmin) / The composite distance TC2 at which MTFave is minimized is not the same. The difference in these lengths is changed to the left or to the right (in the direction in which the object-image distance increases or decreases). Therefore, the composite distance TC1 when the actual object-image distance Tco becomes maximum in the mean value MTFave of the MTF of the rod lens array in the direction of the lens array, and the composite distance TC2 when ΔMTF becomes minimum ), Or MTFave will be maximum so that the deviation amount ΔTC (= | TCo-TC1) |) is within 0 mm <ΔTC <+ 0.2 mm When the composite distance is set, it allows to set it within the allowable range where the average value of the MTF decreases. Therefore, high basic resolution is maintained and uniformity of resolution in the lens array direction is ensured. Thus, optical density nonuniformity can be ignored even when halftone images are handled. In particular, if the deviation amount DELTA TC is set within a range of +0.05 mm ≦ ΔTC ≦ + 0.15 mm, the MTFave is high and the DELTA MTF is low. In other words, good results are obtained.
    [46] Fig. 6 is a graph showing the variation of the mean value MTFave of MTF and ΔMTF 'measured using the rod lens array specified on the basis of the simulation. In the measurement, the full width profile of the MTF at 12 lp / mm is actually measured. The variation of the mean value MTFave between MTF and ΔMTF 'is obtained based on the full width profile of the MTF. ΔMTF 'is mathematically defined as follows.
    [47] ΔMTF '= (MTFave-MTFmin) / MTFave
    [48] [Delta] MTF 'takes the minimum, 10.3 mm at that position when DELTA TC = 0.1 mm with respect to the composite distance TC1 providing the largest MTFave (10.2 mm).
    [49] The variation in the average value MTFave of the MTF and ΔMTF 'of the rod lens array specified as follows is calculated. As a result, the optical system shown in FIG. 4 is used. The MTF full-width profile at 12 lp / mm is measured for various object-image distances Tc. The calculation result is shown in FIG.
    [50] Rod lens diameter D: 0.912 mm
    [51] Composite length providing maximum MTFave (TC1): 15.1 mm
    [52] Rod lens length (Zo): 6.89 mm
    [53] Angular opening (maximum acute angle, Θo: 20 °
    [54] Refractive Index (no): 1.627
    [55] Refractive Index Distribution Factor (g): 0.5348
    [56] [Delta] MTF 'takes the minimum, 14.9 mm at that position when DELTA TC = 0.1 mm with respect to the composite distance TC1 providing the largest MTFave (14.8 mm).
    [57] As can be seen from the above description, in the image forming apparatus of the present invention, the composite distance (when the actual object-image distance Tco becomes maximum in the mean value MTFave of the MTF of the rod lens array in the direction of the lens array) The amount of deviation ΔTC (= | TCo-TC1) |) is 0 mm if it is set between the composite distance TC2 when TC1) and ΔMTF are minimum or the same as the composite distance TC2 when ΔMTF is minimum. If the composite distance is set when the MTFave is maximized to within <ΔTC <+ 0.2 mm, it is allowed to set it within an allowable range in which the average value of the MTF decreases. Therefore, high basic resolution is maintained and uniformity of resolution in the lens array direction is ensured. Thus, optical density nonuniformity can be ignored even when halftone images are handled. In particular, if the deviation amount DELTA TC is set within a range of +0.05 mm ≦ ΔTC ≦ + 0.15 mm, the MTFave is high and the DELTA MTF is low.
    [58] In the present invention, the lens operating distance of the rod lens array to the object side is substantially the same as that of the image side. Unevenness of resolution in the lens array direction is ensured while retaining high resolution. Thus, the nonuniformity of optical density can be ignored even when dealing with halftone images.
    权利要求:
    Claims (6)
    [1" claim-type="Currently amended] A plurality of rod lenses each having a refractive index distribution in the radial direction and arranged such that the optical axes are arranged parallel to each other, wherein the image planes are arranged opposite one end face of the object plane rod lens array and the other In an image forming apparatus using unit expanding imaging rod lenses arranged opposite to end faces, the lens operating distance of the rod lens array on the object side is substantially the same as that on the image side,
    Of the composite distance TC1 when the actual object-image distance Tco is maximum in the mean MTFave of the MTF of the rod lens array in the direction of the lens array, and the composite distance TC2 when the ΔMTF is minimum. Image forming apparatus, characterized in that set between.
    [2" claim-type="Currently amended] The method of claim 1,
    If the actual object-image distance (Tco) is equal to the composite distance (TC2) at which the MTF is the minimum, then the MTFave is adjusted so that the deviation ΔTC (= | TCo-TC1) |) is within 0 mm <ΔTC <+ 0.2 mm. And the compound distance is set when the maximum is reached.
    [3" claim-type="Currently amended] The method of claim 2,
    The actual object-image distance Tco is an image in which the deviation amount DELTA TC is set within a range of +0.05 mm ≦ ΔTC ≦ + 0.15 mm with respect to the composite distance TC1 at which the MTF is minimum. Forming device.
    [4" claim-type="Currently amended] A plurality of rod lenses each having a refractive index distribution in the radial direction and arranged such that the optical axes are arranged parallel to each other, wherein the image planes are arranged opposite one end face of the object plane rod lens array and the other In an image forming apparatus using unit expanding imaging rod lenses arranged opposite to end faces, the lens operating distance of the rod lens array on the object side is substantially the same as that on the image side,
    The actual object-image distance Tco is set so that the compound distance TC1 is set when the MTFave becomes maximum so that the deviation amount ΔTC (= | TCo-TC1) |) is set within 0 mm <ΔTC <+ 0.2 mm. And the composite distance TC2 when MTF (= (MTFmax-MTF min) / MTFave) becomes the minimum.
    [5" claim-type="Currently amended] The method of claim 4, wherein
    The actual object-image distance Tco is an image in which the deviation amount DELTA TC is set within a range of +0.05 mm ≦ ΔTC ≦ + 0.15 mm with respect to the composite distance TC1 at which the MTF is minimum. Forming device.
    [6" claim-type="Currently amended] In the image forming apparatus,
    The rod lens array has a first compound distance TC1 and a second compound distance TC2 where ΔMTF (= (MTFmax − MTF min) / MTFave) becomes minimum when the MTF average MTFave becomes minimum in the lens array direction. And a gradient index rod lenses, which include a rod lens array in which their optical axes are arranged parallel to each other,
    An object surface opposite the end surface of the rod lens array,
    The image plane opposite the other end face of the rod lens array,
    The length TCo between the object plane and the image plane falls within a range between the first compound length TC1 and the second compound length TC2, or
    The length TCo is substantially equal to the second compound length TC2 and is determined by the predetermined amount of deviation (ΔTC (= | TCo-TC1) |) that falls within the range of 0 mm to +0.2 mm. And an image forming apparatus which is arranged biased from TC1).
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    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    法律状态:
    2000-07-07|Priority to JPJP-P-2000-00207380
    2000-07-07|Priority to JP2000207380A
    2001-07-06|Application filed by 이주하라 요죠우, 닛뽄 시트 글래스 가부시끼가이샤
    2002-01-17|Publication of KR20020005458A
    优先权:
    申请号 | 申请日 | 专利标题
    JPJP-P-2000-00207380|2000-07-07|
    JP2000207380A|JP4132599B2|2000-07-07|2000-07-07|Image forming apparatus|
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