JP5227746B2 - Optical scanning unit and image reading apparatus - Google Patents

Description

  The present invention relates to an optical scanning unit and an image reading apparatus using the optical scanning unit.

  2. Description of the Related Art Conventionally, an apparatus using an erecting equal magnification imaging optical system is known as an image reading apparatus such as a scanner. When the erecting equal-magnification imaging optical system is used, the optical scanning unit can be made more compact than in the case of the reduction imaging optical system. An optical scanning unit of an erecting equal-magnification imaging optical system includes a line-shaped light source, an erecting equal-magnification lens array, a line image sensor, and a housing that fixes these at predetermined positions (for example, Patent Documents). 1).

When using an erecting equal-magnification imaging optical system, the best optics are available when the distance between the document and the erecting equal-magnification lens array is the same as the distance between the erecting equal-magnification lens array and the line image sensor. Designed for performance. If the two are not the same, the optical performance deteriorates because the image is blurred. Therefore, considering that the document is a flat surface, the erecting equal-magnification lens array and the line image sensor are also linearly incorporated in the casing so as to be parallel to the document.
JP 2007-1583789 A

  By the way, in the case of an image reading apparatus that reads a document by scanning a scanning unit on a glass plate on which the document is placed, the distance between the document and the erecting equal-magnification lens array, the erecting equal-magnification lens array, and the line image If the distance between the sensors is to be the same, a certain distance is required between the glass plate and the optical scanning unit. Therefore, the optical scanning unit has an erecting equal-magnification lens array rather than the center of the housing. The structure is provided on the side.

  Here, considering a method of fixing the erecting equal-magnification lens array to the housing, a method is conceivable in which a recess is formed on the document side surface of the housing and the erecting equal-magnification lens array is inserted into the recess. Usually, the housing is manufactured by resin injection molding in consideration of the ease of manufacturing and cost, but the width of the recess is formed to be approximately the same as the width of the erecting equal-magnification lens array, and the recess is expanded. The erecting equal-magnification lens array is inserted while opening. According to this method, the erecting equal-magnification lens array can be fixed at a predetermined position without performing precise alignment.

  However, when an elongated part such as a scanning unit casing is manufactured by injection molding, it is difficult to keep the width of the concave portion constant in the longitudinal direction of the casing. Specifically, the width of the concave portion at the central portion in the longitudinal direction tends to be formed narrower than the width of the concave portion at the end portion. When the erecting equal-magnification lens array is inserted into the concave portion formed in this way, the erecting equal-magnification lens array is likely to be warped so as to be convex toward the document side. Therefore, since the distance between the original and the erecting equal-magnification lens array and the distance between the erecting equal-magnification lens array and the line image sensor differ depending on the position in the main scanning direction, the optical performance varies in the main scanning direction. There is a possibility that.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an optical scanning unit capable of reducing fluctuations in optical performance in the main scanning direction, and an image reading apparatus using the optical scanning unit. There is.

  In order to solve the above problems, an optical scanning unit according to an aspect of the present invention includes a line-shaped light source that irradiates light on a document, an erecting equal-magnification lens array that collects reflected light from the document, erecting, etc. An optical scanning unit including a line image sensor that receives light collected by the double lens array, and a housing that fixes the linear light source, the erecting equal-magnification lens array, and the line image sensor. In the main scanning direction of the optical scanning unit, it is warped so as to be convex toward the line image sensor.

  According to this aspect, since the case is warped so as to be convex toward the line image sensor in the main scanning direction of the optical scanning unit, the warp that is convex toward the document side of the erecting equal-magnification lens array is offset. Therefore, it is compensated that the distance between the original and the erecting equal-magnification lens array and the distance between the erecting equal-magnification lens array and the line image sensor differ depending on the position in the main scanning direction. As a result, variation in optical performance in the main scanning direction can be reduced.

  The housing may have a recess opened on the document side, and the erecting equal-magnification lens array may be fixed to the document side with respect to the center of the housing by being fitted into the recess. The housing may be formed by resin injection molding. In the optical scanning unit using the casing formed in this way, fluctuations in optical performance in the main scanning direction can be reduced particularly effectively.

  The case may have a warp ratio in a range of 0.02% to 0.06%, which is a ratio of a warp amount in the center of the main scanning direction to a length of the case in the main scanning direction. By warping the casing so as to be within such a range, it is possible to suitably reduce fluctuations in optical performance in the main scanning direction.

  Another aspect of the present invention is an image reading apparatus. This apparatus includes a document table on which a document is placed, the above-described optical scanning unit, and a drive mechanism that scans the optical scanning unit.

  According to this aspect, it is possible to configure an image reading apparatus in which blurring of an image in the main scanning direction is suppressed by using the optical scanning unit in which fluctuations in optical performance in the main scanning direction are reduced.

  It should be noted that any combination of the above-described constituent elements and a representation obtained by converting the expression of the present invention between a method, an apparatus, a system, and the like are also effective as an aspect of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the optical scanning unit which can reduce the fluctuation | variation of the optical performance in a main scanning direction, and an image reading apparatus using this optical scanning unit can be provided.

  FIG. 1 is a diagram for explaining an image reading apparatus 100 using an optical scanning unit 10 according to an embodiment of the present invention. As shown in FIG. 1, the image reading apparatus 100 includes an optical scanning unit 10, a glass plate 14 as a document table on which an original G is placed, a driving mechanism (not shown) that scans the optical scanning unit 10, and an optical scanning unit. 10 includes an image processing unit (not shown) that processes the data read by the computer 10.

  The optical scanning unit 10 includes a line-shaped light source 16 that irradiates light on a document G placed on a glass plate 14, an erecting equal-magnification lens array 11 that collects reflected light from the document G, and erecting etc. A line image sensor (photoelectric conversion element) 20 that receives the light collected by the double lens array 11, and a housing 12 that fixes the line light source 16, the erecting equal-magnification lens array 11, and the line image sensor 20 are provided.

  The housing 12 is formed in a substantially rectangular parallelepiped shape. A first recess 12a and a second recess 12b are formed on the upper surface of the housing 12, and a third recess 12c is formed on the lower surface. The housing 12 is formed by resin injection molding. By forming the casing 12 by injection molding, the casing 12 can be easily formed and inexpensive. A linear light source 16 is fixed obliquely in the first recess 12a. The line light source 16 is fixed so that the optical axis of the irradiation light passes through the intersection of the optical axis Ax of the erecting equal-magnification lens array 11 and the upper surface of the glass plate 14.

  The erecting equal-magnification lens array 11 is fixed to the second recess 12b. A method for fixing the erecting equal-magnification lens array 11 will be described later. A substrate 22 including a line image sensor 20 is attached to the third recess 12c. The substrate 22 is fixed so that the upper surface thereof is in contact with the stepped portion 12d provided in the third recess 12c.

  The erecting equal-magnification lens array 11 is laminated so that a pair of lenses corresponding to a first lens array plate 24 and a second lens array plate 25 each having a plurality of convex lenses formed on both sides constitute a coaxial lens system. Is. The first lens array plate 24 and the second lens array plate 25 are held in a stacked state by a holder 30. The erecting equal-magnification lens array 11 receives substantially linear light reflected from the document G located above, and forms an erecting equal-magnification image on the image surface located below, that is, the light receiving surface of the line image sensor 20. It is configured to form.

  FIG. 2 is a cross-sectional view of the image reading apparatus 100 in the sub-scanning direction. FIG. 3 is a cross-sectional view of the image reading apparatus 100 in the main scanning direction. 2 and 3, the line-shaped light source 16 is not shown. As shown in FIGS. 2 and 3, the optical scanning unit 10 is mounted on the image reading apparatus 100 such that the longitudinal direction thereof coincides with the main scanning direction and the short side direction thereof coincides with the sub scanning direction. In the image reading apparatus 100, the light emitted from the line light source is applied to the original G through the glass plate 14, and the reflected light from the original G is detected by the line image sensor 20 via the erecting equal-magnification lens array 11. Thus, the original G is read. By scanning the casing 12 with respect to the glass plate 14 in the sub-scanning direction, a desired area of the original G can be read.

  In general, in an optical scanning unit using an erecting equal-magnification imaging optical system, a distance a between an original and an erecting equal-magnification lens array (hereinafter referred to as an original / lens distance a) and an erecting equal-magnification lens It is designed so that the best optical performance is obtained when the distance b between the array and the line image sensor (hereinafter referred to as the lens / sensor distance b) is the same. If they are not the same, the image formed on the line image sensor 20 will be blurred, resulting in poor optical performance. The document / lens distance a is precisely the distance from the lower surface of the document G to the convex lens on the upper surface of the first lens array plate 24, and the lens / sensor distance b is precisely the second lens array plate. 25 is a distance from the convex lens on the lower surface of 25 to the light receiving surface of the line image sensor 20. Further, since the refractive index is actually larger in the glass plate 14 than in the air, the document / lens distance a is shorter than the lens / sensor distance b.

  If the document / lens distance a and the lens / sensor distance b are made the same as described above, a certain amount of space is required between the glass plate 14 and the optical scanning unit 10. The erecting equal-magnification lens array 11 is provided on the document side with respect to the center of the housing. In other words, in the normal direction of the document G, the center of the erecting equal-magnification lens array 11 is positioned closer to the document side than the center of the optical scanning unit 10. By adopting such a structure, even when a gap is provided between the glass plate 14 and the optical scanning unit 10, the document / lens distance a and the lens / sensor distance b can be made equal. .

  FIGS. 4A and 4B are top views for explaining how the erecting equal-magnification lens array 11 is attached to the housing 12. 4A shows a state before the erecting equal-magnification lens array 11 is attached to the housing 12, and FIG. 4B shows a state after the erecting equal-magnification lens array 11 is attached to the housing 12. Indicates. FIG. 5 is a cross-sectional view in the sub-scanning direction for explaining how the erecting equal-magnification lens array 11 is attached to the housing 12.

  The second recess 12b of the housing 12 is formed such that the width in the short direction (sub-scanning direction) is substantially the same as the width in the short direction of the erecting equal-magnification lens array 11. When the erecting equal-magnification lens array 11 is attached to the housing 12, the erecting equal-magnification lens array 11 is fitted into the second recess 12b while expanding the second recess 12b as shown by arrows 60 and 61 in FIG. To do. According to this method, the erecting equal-magnification lens array 11 can be fixed at a predetermined position without performing precise positioning. Here, when the erecting equal-magnification lens array 11 is fitted into the second recess 12b, as shown by an arrow 63 in FIG. 5, the upper side (the document side when attached to the image reading apparatus 100) is shown. The push output is being received.

  As described above, the casing 12 is formed by injection molding. However, when an elongated part such as the casing 12 is manufactured by injection molding, the width of the second recess 12b is made constant in the longitudinal direction of the casing 12. Difficult to keep. Specifically, as shown in FIG. 5A, the width of the second recess 12b at the center in the main scanning direction (longitudinal direction) tends to be narrower than the width of the recess at both ends. When the erecting equal-magnification lens array 11 is inserted into the second recess 12b formed in this manner, the erecting equal-magnification lens array 11 receives a stronger pushing force than both ends at the center in the main scanning direction. There is a high possibility of warping so that it floats most toward the document side and protrudes toward the document side at the center in the main scanning direction. In this case, since the document / lens distance a and the lens / sensor distance b differ depending on the position in the main scanning direction, the optical performance varies in the main scanning direction.

  While considering the above problems, the present inventor considered whether or not the fluctuation in the main scanning direction of the optical performance could be suppressed by warping the housing 12 in the main scanning direction. In the following description, when the erecting equal-magnification lens array 11 is warped so as to be convex toward the original, it is preferable that the casing 12 be warped so as to be convex toward either the original or the line image sensor 20. Explain that. Here, there is a possibility that the line image sensor 20 is also warped in the main scanning direction. As a cause of the warp of the line image sensor 20, there are a case where the substrate 22 is originally warped, a case where the line image sensor 20 is attached to the substrate 22, and the like. Note that the glass plate 14 is formed in a flat surface without warping, and therefore the document G placed on the glass plate 14 is also described as a flat surface.

  FIG. 6 is a diagram for explaining the ratio between the document / lens distance a and the lens / sensor distance b when the line image sensor 20 is not warped. In FIG. 6, the optical scanning unit 10 is illustrated in a simplified manner. Here, when the document / lens distance a and the lens / sensor distance b at both ends in the main scanning direction are 1.0, the erecting equal-magnification lens array 11 is warped so as to be convex toward the document side. Assume that the lens / sensor distance b in the center of the main scanning direction is 1.1 and the document / lens distance a is 0.9. At this time, b / a, which is the ratio of the document / lens distance a and the lens / sensor distance b, is 1.222. The closer the distance ratio b / a is to 1.0, the closer the optical performance at the center in the main scanning direction is to the optical performance at both ends.

  Here, by warping the casing 12 so as to be convex toward the original, the erecting equal-magnification lens array 11 fixed to the casing 12 is also warped so as to be convex toward the original, and the original in the center of the main scanning direction / Assume that the distance a between lenses is reduced to 0.8. The lens / sensor distance b does not change because the erecting equal-magnification lens array 11 and the line image sensor 20 are both warped so as to be convex toward the original, and remains 1.1. In this case, the distance ratio b / a is 1.375, which is larger than the above-mentioned 1.222.

  On the other hand, when the casing 12 is warped so as to be convex toward the line image sensor 20, the erecting equal-magnification lens array 11 is also warped so as to be convex toward the line image sensor 20, and the original / lens in the center of the main scanning direction. It is assumed that the distance a is increased to 1.0. The lens / sensor distance b is 1.1. In this case, the distance ratio b / a is 1.100, which is smaller than the above-mentioned 1.222.

  FIG. 7 is a diagram for explaining the ratio between the document / lens distance a and the lens / sensor distance b when the line image sensor 20 is warped to be convex toward the document. Here, when the document / lens distance a and the lens / sensor distance b at both ends in the main scanning direction are set to 1.0, the erecting equal-magnification lens array 11 is warped so as to be convex toward the document side, and further the line It is assumed that the document / lens distance a at the center of the main scanning direction becomes 0.9 and the lens / sensor distance b becomes 1.0 by warping the image sensor 20 to be convex toward the document side. At this time, the distance ratio b / a is 1.111.

  Here, by warping the casing 12 so as to be convex toward the original, the erecting equal-magnification lens array 11 fixed to the casing 12 is also warped so as to be convex toward the original, and the original in the center of the main scanning direction / Assume that the reduction of the distance a between lenses is 0.8. The lens / sensor distance b does not change because the erecting equal-magnification lens array 11 and the line image sensor 20 are both warped so as to be convex toward the original, and remains 1.0. In this case, the distance ratio b / a is 1.25, which is larger than the above 1.111.

  On the other hand, by warping the housing 12 so as to be convex toward the line image sensor 20, the erecting equal-magnification lens array 11 is also warped so as to be convex toward the line image sensor 20, and the document / lens in the center of the main scanning direction It is assumed that the distance a is increased to 1.0. The lens / sensor distance b is 1.0. In this case, the distance ratio b / a is 1.0, which is smaller than the aforementioned 1.111.

  FIG. 8 is a diagram for explaining the ratio between the document / lens distance a and the lens / sensor distance b when the line image sensor 20 is warped so as to be convex on the side opposite to the document side. Here, when the document / lens distance a and the lens / sensor distance b at both ends in the main scanning direction are set to 1.0, the erecting equal-magnification lens array 11 is warped so as to be convex toward the document side, and further the line When the image sensor 20 is warped so as to be convex on the side opposite to the document side, the document / lens distance a in the center of the main scanning direction becomes 0.9 and the lens / sensor distance b becomes 1.2. Suppose. At this time, the distance ratio b / a is 1.333.

  Here, by warping the casing 12 so as to be convex toward the original, the erecting equal-magnification lens array 11 fixed to the casing 12 is also warped so as to be convex toward the original, and the original in the center of the main scanning direction / Assume that the reduction of the distance a between lenses is 0.8. The lens / sensor distance b does not change because both the erecting equal-magnification lens array 11 and the line image sensor 20 are warped so as to be convex toward the document side, and remains 1.2. In this case, the distance ratio b / a is 1.5, which is larger than the above-mentioned 1.333.

  On the other hand, by warping the housing 12 so as to be convex toward the line image sensor 20, the erecting equal-magnification lens array 11 is also warped so as to be convex toward the line image sensor 20, and the document / lens in the center of the main scanning direction It is assumed that the distance a is increased to 1.0. The lens / sensor distance b remains 1.2. In this case, the distance ratio b / a is 1.2, which is smaller than the above-mentioned 1.333.

  As described with reference to FIGS. 6 to 8, when the erecting equal-magnification lens array 11 is warped so as to be convex toward the original, the housing 12 is line-shaped regardless of the direction in which the line image sensor 20 warps. The distance ratio b / a at the center in the main scanning direction becomes smaller as it warps toward the image sensor 20, and approaches 1.0. That is, since the optical performance in the center of the main scanning direction is close to the optical performance at both ends, the fluctuation of the optical performance in the main scanning direction is reduced.

  From the above consideration, in the optical scanning unit 10 according to the present embodiment, the housing 12 is formed so as to warp convex toward the line image sensor 20 in the main scanning direction. That is, the housing 12 is formed such that the central portion in the main scanning direction is displaced toward the attachment side of the line image sensor 20 rather than the straight line connecting both ends in the main scanning direction. As a result, the warp of the erecting equal-magnification lens array 11 convex toward the original is canceled, so that the difference between the original / lens distance a and the lens / sensor distance b differs depending on the position in the main scanning direction. The As a result, variation in optical performance in the main scanning direction can be reduced. Further, by using the optical scanning unit 10 in which fluctuations in optical performance in the main scanning direction are reduced, it is possible to configure the image reading apparatus 100 in which image blurring in the main scanning direction is suppressed.

  FIG. 9 is a diagram illustrating the relationship between the warp ratio of the housing 12 and the optical performance. It was experimentally verified how much the casing 12 is warped to the line image sensor 20 side to compensate for the warp of the erecting equal-magnification lens array 11 and to suppress a decrease in optical performance.

  The optical performance was judged by the MTF value (6 line / mm). The erecting equal-magnification lens array 11 and the line image sensor 20 were attached to the housing 12, and the MTF value was measured. Each warp ratio of the housing 12 was sorted as shown in FIG. 9, and 100 pieces were selected for each to measure the MTF value. Those having an MTF value of 70% or more are counted as non-defective products and are shown in FIG. The warpage ratio is the ratio (percentage) of the warpage amount at the center in the main scanning direction to the length of the housing 12 in the main scanning direction. As a result, as shown in FIG. 9, it was found that a non-defective product can be manufactured nearly 100% by setting the warp ratio of the casing 12 within the range of 0.02% to 0.06%.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

It is a figure for demonstrating the image reading apparatus using the optical scanning unit which concerns on embodiment of this invention. FIG. 3 is a cross-sectional view of the image reading apparatus in the sub-scanning direction. FIG. 3 is a cross-sectional view of the image reading apparatus in the main scanning direction. FIGS. 4A and 4B are top views for explaining a state in which the erecting equal-magnification lens array is attached to the housing. It is sectional drawing in the subscanning direction for demonstrating a mode at the time of attaching an erecting equal-magnification lens array to a housing | casing. It is a figure for demonstrating ratio of the document / lens distance a and the lens / sensor distance b in case the line image sensor is not curled. FIG. 5 is a diagram for explaining a ratio between a document / lens distance a and a lens / sensor distance b when the line image sensor is warped to be convex toward the document side. FIG. 6 is a diagram for explaining a ratio between a document / lens distance a and a lens / sensor distance b when the line image sensor is warped so as to be convex on the side opposite to the document side. It is a figure which shows the relationship between the curvature ratio of a housing | casing, and optical performance.

Explanation of symbols

  10 optical scanning unit, 11 erecting equal-magnification lens array, 12 housing, 16 line light source, 20 line image sensor, 100 image reading device, G document.

Claims (5)

A line-shaped light source for irradiating light on a document;
An erecting equal-magnification lens array for collecting the reflected light from the original;
A line image sensor that receives light collected by the erecting equal-magnification lens array;
A housing for fixing the line-shaped light source, the erecting equal-magnification lens array, and the line image sensor;
An optical scanning unit comprising:
The housing has a recess opened on the document side, and the erecting equal-magnification lens array is fixed to the document side from the center of the housing by being fitted into the recess,
The concave portion is formed such that the width at the center in the main scanning direction is narrower than the width at the end,
The optical scanning unit, wherein the casing is warped so as to protrude toward the line image sensor in the main scanning direction of the optical scanning unit. 2. The optical scanning unit according to claim 1, wherein the optical scanning unit is configured to be attached to an image reading apparatus so that the original is positioned above and the line image sensor is positioned below. Wherein the housing includes an optical scanning unit according to claim 1 or 2, characterized in that it is formed by injection molding of resin. The warp ratio, which is a ratio of a warp amount at the center of the main scanning direction to a length of the housing in the main scanning direction, is in a range of 0.02% to 0.06%. Item 4. The optical scanning unit according to any one of Items 1 to 3 . An original table on which an original is placed;
An optical scanning unit according to any one of claims 1 to 4 ,
A drive mechanism for scanning the optical scanning unit;
An image reading apparatus comprising:

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