JP2014182325A - Imaging optical device, contact type image sensor module and image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a contact type image sensor module that does not use a refraction distribution type lens, which is able to restrict ghost formed on an image face.SOLUTION: An imaging optical device comprises: a lens member in which a plurality of lens faces 30a, 30b for forming erecting unmagnified images of an object on specific image faces are formed on the object side and the image face side, one on each side; and light shielding members 20, 21 arranged on the object side and image face side of the lens member, one at each side, and having a plurality of through holes 201, 211 through which the respective optical axes of the different lens faces pass. The image face side through hole has a lens face side aperture 211a at a position further away from the lens face by a predetermined margin distance from the intersection furthest from the lens face of the intersections of a target light beam passing through the object side through-hole formed on an optical axis passing through the through-holes and also passing through the periphery of the image face side lens face having the optical axis, with ghost light beams G1, G2 that are not target light beams passing through the periphery of the image face side lens face having the light source.

Description

  The present invention relates to an imaging optical device, a contact-type image sensor module, and an image reading device.

  Conventionally, a contact-type image sensor module that does not use a gradient index lens such as a SELFOC (registered trademark) lens array is known. In a contact-type image sensor module that does not use a gradient index lens, a light shielding member having a through hole is provided between the lens member and the object and between the lens member and the image plane.

JP 2007-57995 A JP 2000-214305 A

  In a contact-type image sensor module that does not use a gradient index lens, it is a problem to suppress ghosts formed on the image plane.

  The imaging optical device according to the present invention includes a lens member in which a plurality of lens surfaces each connecting an erecting equal-magnification image of an object to a predetermined image surface are formed on the object side and the image surface side, and A light-shielding member that is disposed on each of the object side and the image plane side of the lens member and has a plurality of through holes through which optical axes of the lens surfaces different from each other are formed. The through hole includes a target light beam passing through the through hole on the object side formed on an optical axis passing through the through hole and an outer periphery of the lens surface on the image plane side having the optical axis, and the optical axis. Among the intersection points with the ghost rays that are not the target rays passing through the outer periphery of the lens surface on the image plane side, the lens surface at a position further away from the lens surface by a predetermined margin distance from the intersection farthest from the lens surface With side opening .

  According to the present invention, since the light shielding member on the image surface side is away from the lens surface to a position where the ghost light included in the light passing through the lens surface through which the target light beam passes can be separated from the lens surface, the ghost is significantly reduced. Can be suppressed. A ghost ray is a ray that forms a ghost on the image plane when it reaches the image plane.

  Here, the position of the opening on the lens surface side of the through hole on the image surface side is closer to the lens member, and light passing through the lens surface that is not the lens surface through which the optical axis passes through the through hole is incident on the through hole. It becomes difficult. However, the inventor of the present application has found that a ghost ray that forms a ghost in the image plane is also included in the light passing through the lens surface through which the target ray passes. Further, the inventor of the present application pays attention to the fact that the angle formed by the ghost light beam with respect to the optical axis of the lens surface is larger than the angle formed by the target light beam with respect to the optical axis of the lens surface. It was discovered that the ghost can be suppressed by moving the position away from the lens member to some extent. That is, the position of the aperture on the lens surface side of the through hole on the image plane side is the intersection of the target beam and a ghost beam that is not the target beam passing through the outer periphery of the lens surface on the image plane side through which the optical axis passes through the through hole. Among them, the ghost can be suppressed by setting the intersection farthest from the lens surface. Therefore, the position of the opening on the lens surface side of the through hole on the image surface side is set at a position further away from the lens surface from the intersection by a predetermined margin distance corresponding to the manufacturing tolerance.

  In addition, the width of the opening on the lens surface side of the through hole on the image surface side is preferably as narrow as possible within the range through which the target light beam can pass, and thus is the width of the target light beam at the opening position. Thus, a ghost can be suppressed by setting the position and width of the opening on the lens surface side of the through hole on the object side.

  In addition, when the light from one point of the object is designed to form an image on the image plane through the three lenses, the light passing through the middle lens among the three lenses is in the through hole on the image plane side. Since it is difficult to hit the wall, ghosts are unlikely to occur. However, the light passing through the lenses on both sides of the middle lens passes through the through hole at an angle determined by the lens pitch with respect to the lens-image distance. For this reason, it may hit the inner wall surface of the through hole on the image plane side, and the amount of light may decrease. Therefore, it is preferable to provide a taper on the inner wall surface of the through hole on the image plane side so that light of this angle does not strike. In other words, it is preferable that the width of the through hole on the image plane side is wider in the image plane direction than the bundle of target rays that have passed through the opening on the lens plane side.

Sectional drawing concerning embodiment of this invention. The top view concerning embodiment of this invention. The light ray figure concerning embodiment of this invention. The elements on larger scale of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the corresponding component in each figure, and the overlapping description is abbreviate | omitted.

1. Image Reading Device FIG. 1 shows a main part of an image reading device 1 as a position example of the present invention. The image reading device 1 includes a contact-type image sensor module including the imaging optical device 2 and the linear image sensor 40, a platen glass 10, an analog-digital converter (not shown), a sub-scanning mechanism, a control unit, and the like.

  A platen glass 10 as a positioning member is a transparent flat glass for positioning a document 9 as an object with respect to the imaging optical device 2. The linear image sensor 40 as an imaging element has a light receiving surface 40 a that is parallel to the platen glass 10 and faces the platen glass 10. A large number of photoelectric conversion elements (not shown) are linearly arranged on the light receiving surface 40a serving as the image plane of the object. The arrangement direction of the photoelectric conversion elements is the main scanning direction, and the direction orthogonal to this is the sub-scanning direction. The imaging optical device 2 includes a first light shielding member 20 on the object side, a lens member 30, and a second light shielding member 21 on the image plane side. The imaging optical device 2 is disposed between the platen glass 10 and the linear image sensor 40 so as to form an erecting equal-magnification image on the light receiving surface 40a of the linear image sensor 40.

  The lens member 30 is a transparent resin member in which a large number of lens surfaces 30a and 30b are linearly arranged on each of two opposing end surfaces. The end surface on the object side and the end surface on the image plane side of the lens member 30 have the same shape. That is, the lens surface 30a on the object side of the lens member 30 and the lens surface 30b on the image surface side of the lens member 30 have the same shape, and the arrangement of the lens surfaces 30a and 30b on the respective end surfaces is also the same. .

  The first light shielding member 20 and the second light shielding member 21 disposed on both sides of the lens member 30 are plate-like members made of an opaque resin manufactured by injection molding. The first light shielding member 20 is disposed between the lens member 30 and the platen glass 10 in parallel with the light receiving surface 40 a of the linear image sensor 40. The second light shielding member 21 is disposed between the lens member 30 and the linear image sensor 40 in parallel with the light receiving surface 40 a of the linear image sensor 40. A large number of through holes 201 and 211 are linearly arranged in the light shielding members 20 and 21, respectively. The optical axes of different lens surfaces 30a and 30b pass through the through holes 201 and 211, respectively.

2. Details of Imaging Optical Device FIG. 2A shows the contours of the lens surfaces 30a and 30b viewed from the optical axis direction of the lens surfaces 30a and 30b. FIG. 2B shows the outlines of the through holes 201 and 211 as seen from the optical axis direction of the first light shielding member 20 and the second light shielding member 21. The arrangement direction and arrangement interval of the through holes 201 and 211 coincide with the arrangement direction and arrangement interval of the lens surfaces 30a and 30b. The arrangement direction of the through holes 201 and 211 and the arrangement direction of the lens surfaces 30a and 30b coincide with the main scanning direction.

  The lens surfaces 30a and 30b are formed of spherical surfaces whose both ends are cut off by a plane perpendicular to the arrangement direction of the lens surfaces 30a and 30b and intersecting each other on the adjacent lens surfaces 30a and 30b. Therefore, compared to a configuration in which the circumferences of adjacent lens surfaces are in contact with each other, large lens surfaces 30 a and 30 b can be densely arranged on the end surface of the lens member 30. As a result, the irradiance of the light receiving surface 40a can be increased and illuminance unevenness can be reduced.

  The through holes 201 and 211 have a rectangular shape whose cross section perpendicular to the optical axis is short in the arrangement direction of the lens surfaces 30a and 30b. If the corner is rounded, resin molding is easy. Each of the inner wall surfaces of the through holes 201 and 211 is a flat surface, but may be a curved surface. Since these inner wall surfaces need to have a light absorbing function, it is desirable to use a light absorbing member as the member, and specifically, a black resin or the like is preferable. It is also preferable that the surface of the inner wall surface has fine irregularities. Similarly to the openings of the through holes 201 and 211, the widths of the lens surfaces 30a and 30b are narrow in the arrangement direction of the lens surfaces 30a and 30b and wide in the direction orthogonal to the arrangement direction. As described above, since the opening shapes of the through holes 201 and 211 correspond to the shapes of the lens surfaces 30a and 30b, the light beam emitted from the through hole 201 on the object side can be efficiently incident on the lens surface 30a. In addition, the light beam emitted from the lens surface 30b can be efficiently incident on the through hole 211 on the image surface side. Thereby, the irradiance of the light receiving surface 40a can be increased.

3 and 4 show the positions of the light shielding members 20 and 21 with respect to the lens member 30 in the optical axis direction. The distance d ₇ from the lens member 30 to the surface 10a of the platen glass and the distance d ₈ from the lens member 30 to the light receiving surface 40a of the linear image sensor are the same as the optical distance. If the refractive index of the platen glass is n _p and the thickness is d _p , d ₇ becomes longer by d _p (n _p −1) in terms of physical distance. Therefore, the physical distance is d ₇ = d ₈ + d _p (n _p −1), but is ignored here for easy understanding. The first light shielding member 20, the lens member 30, and the second light shielding member 21 have a central axis of the through hole 20 a of the first light shielding member 20 and a central axis of the through hole 21 a of the second light shielding member 21, as indicated by the alternate long and short dash line. And the optical axis of the lens surface 30a and the optical axis of the lens surface 30b are arranged to coincide with each other.

As the distance between the first light shielding member 20 and the lens member 30 is shorter, ghost light is less likely to enter the lens surface 30a. Therefore, the distance d ₉ between the first shielding member 20 and the lens member 30 is set as small as possible. In addition, since the manufacturing cost of the first light shielding member 20 can be reduced by forming by injection molding, and the ghost light is less likely to be incident as the opening on the image plane side is narrow, it is preferable to narrow the opening on the image plane side. However, it is preferable that the through hole 201 extends in the direction from the platen glass 9 toward the lens member 30 in accordance with the spread of the bundle of target beams so as not to block the target beam.

When the second light shielding member 21 is closer to the lens member 30, ghost light that has passed through the lens surface 30 b that is not the lens surface 30 b ₀ through which the optical axis passes through the through hole 211 of the second light shielding member 21 enters the through hole 211. It becomes difficult. However, some of the light rays passing through the lens surface 30b ₀ which the optical axis passes through the through hole 211 may also be included ghost light G1, G2 indicated by the dotted line and two-dot chain line. For this reason, if the second light shielding member 21 is too close to the lens member 30, such ghost rays G1 and G2 enter the through hole 211.

Optical axis angle shown ghost rays of light outgoing from the lens surface 30b ₀ through the target light beam by a one-dot chain line of the lens surface 30b ₀ is greater than the optical axis angle indicated target light beam by a chain line of the lens surface 30b ₀ . Thus the ghost light exits outside of the bundle of target light some extent away from the lens surface 30b _0. Therefore in preventing the ghost light is incident on the through hole 211 to the farthest intersection from the lens surface 30b ₀ of intersection of the target light and ghost light passing through the periphery of the lens surface 30b _0, through the lens surface 30b ₀ The opening 211a of the hole 211 may be separated. As that ghost light passes a lens surface 30b ₀ is far from the optical axis, the intersection with the target light beam passing through the periphery of the ghost light and the lens surface 30b ₀ is the distance from the lens surface 30b _0.

Ghost light is 3, as shown by a dotted line in FIG. 4, beam G1 passing through the through hole 211 adjacent to the through hole 211 of the object side through the target light ray passing through the first lens surface 30b ₀ on the image side Can be included. The ghost light is, as indicated by the two-dot chain line in FIG. 3, may include a light G2 reflected at the inner wall surface of the through-hole 201 of the object side through the target light ray passing through the first lens surface 30b ₀ on the image side .

In this embodiment, as shown in FIGS. 3 and 4, the ghost light beam G1 that has passed through the adjacent through hole 201 rather than the ghost light beam G2 reflected by the inner wall surface of the through hole 201 on the object side through which the target light beam passes. Is smaller in angle with the optical axis of the lens surface 30b. Intersection Q of the target light beam passing through the periphery of the ghost light G1 and the lens surface 30b ₀ 4 therefore, than the intersection point P of the target light beam passing through the periphery of the ghost light G2 and a lens surface 30b _0, the lens surface It is far from 30b. Note that the ghost light G2 reflected at the inner wall surface of the through-hole 201 of the object side through the target light in a ghost light G1 passing through the through hole 201 of the adjacent, towards Which the outer periphery of the lens surface 30b ₀ Whether the intersection with the passing target light beam is far from the lens surface 30b is determined by the arrangement interval of the through holes 201, the inclination angle of the inner wall surface, and the like.

  Depending on the inner wall surface shape of the through-hole 201 on the object side, on the object side of the lens member 30, the image plane passes through the through-hole 201 that is neither the through-hole 201 through which the target light beam passes nor the adjacent through-hole 201. Ghost light can also include ghost light G3 incident on the through-hole 211 through which the target light beam passes, but such ghost light G3 is reflected at the inner wall surface of the through-holes 201 and 211 at an angle that is reflected multiple times. Enter 211. Since the inner wall surfaces of the through holes 201 and 211 are members that absorb light, they are greatly attenuated by being reflected a plurality of times, and substantially no ghost is formed on the image plane.

Therefore, in this embodiment, the target beam passing through the two through-holes 201 and 211 having the same hole axis and the outer periphery of the lens surface on the image plane side, and the through-hole 201 on the object side through which the target beam passes. and intersections of the ghost light reflected by the inner wall surface through the outer periphery of the lens surface 30b _0, of the intersection of the ghost light and its target light passing through the periphery of the through hole 201 and the lens surface 30b ₀ of the next lens surface to set the position of the opening 211a of the through hole 211 of the image plane side to the farthest intersection Q from 30b _0. Incidentally, it will set the actually position of the opening 211a at a position away from the lens surface 30b ₀ than the intersection point Q by a margin distance worth of consideration of tolerance.

Further, in order to prevent the ghost light beam that has passed through the lens surface 30b ₁ adjacent to the lens surface 30b ₀ through which the target light beam passes from entering the through hole 211, the width of the opening 211a is set so that the entire bundle of target light beams passes through the through hole 211. The narrowest width that can be incident is set, or the width is set slightly wider than the width by the margin considering the tolerance. Thus, the ghost light G2 passing through the lens surface 30b ₀ next to the lens surface 30b ₁ through which the target light, it becomes possible to shield at a point R of the end face of the second light-shielding member 21.

Further, the inner wall surface of the through hole 211 on the object side may be set to a shape that does not intersect with the target light beam incident from the opening 211a of the through hole 211 at least. That is, the angle formed by the inner wall surface of the through hole 211 on the object side and the optical axis of the lens surface 30b is θ, the arrangement interval of the lens surfaces 30b is d ₅ , and the distance from the lens surface 30b to the image surface 40a is d ₈ . Then, you may be set so as to satisfy the _{tanθ> d} 5 / d _8. The through hole 211 may be narrowed toward the image plane side, may be widened, or may be a straight hole. However, the straight hole makes injection molding difficult, and when the light from one point on the document surface is collected by a plurality of lenses, the target light does not easily enter the inner wall surface of the through hole 211. For example, when designing so that light from one point on the document surface is collected by a maximum of three lenses (see the light ray G4 in FIG. 4), the lens-light receiving surface distance d ₁₀ , the lens pitch d ₅ , and the rear aperture inner wall taper angle If θ ₂ , tan θ ₂ > d ₅ / d ₁₀ may be satisfied. On the other hand, if the opening 211b on the image plane side of the through-hole 211 is too wide, the second light shielding member 21 cannot be molded, so that tan θ> d ₅ / d ₈ is satisfied and the second light shielding member 21 can be molded. It is only necessary to increase θ in the range and widen the through hole 211 toward the image plane side.

An example of set dimensions that satisfy the above conditions is as follows.
Platen glass thickness d ₁ : 2.8 mm
Refractive index of platen glass: 1.52
Thickness d ₂ of the first light shielding member: 0.66 mm
Second light shielding member thickness d ₃ : 0.5 mm
Lens member thickness d ₄ : 2.68 mm
Lens surface arrangement interval d ₅ : 0.35 mm
Refractive index of lens member: 1.53
Lens surface diameter: 0.588mm
Radius of curvature of lens surface: 0.4mm (Aspheric coefficient is omitted)
Distance from document surface to image surface d ₆ : 10.81 mm
Distance from document surface to lens member d ₇ : 4.46 mm
Distance from lens member to image plane d ₈ : 3.45 mm
Distance d ₉ from the lens member to the first light shielding member: 0 mm
Distance d ₁₀ from the lens member to the second light shielding member: 0.82 mm
Opening size on the object side of the through hole on the image plane side (second light shielding member 21): 0.3 mm × 0.15 mm
Opening size on the image plane side of the through hole on the image plane side (same as above): 1.1 mm × 0.161 mm

  According to the embodiment described above, since the light shielding member on the image plane side is away from the lens surface to a position where the ghost light included in the light passing through the lens surface through which the target light beam passes can be separated from the lens surface, Ghosts can be remarkably suppressed.

3. Other Embodiments The technical scope of the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the scope of the present invention.

For example, the width in the sub-scanning direction of the through holes 211 and 211 may be increased toward the image plane. Thereby, it is possible to suppress the ghost beam having the point shifted from the origin of the target beam in the sub-scanning direction from being reflected by the inner wall surfaces of the through holes 211 and 211 and entering the light receiving surface 40a of the linear image sensor 40. Further, the manufacturing cost may be reduced by matching the shapes of the first light shielding member 20 and the second light shielding member 21 within a range satisfying tan θ> d ₅ / d ₈ . Further, two or more rows of through holes may be formed in the light shielding member.

Of course, materials such as a lens member, a light shielding member, and a platen are examples, and the platen may be formed of resin, the lens member may be formed of glass, or the light shielding member may be formed of metal. good. Further, the lens surfaces may be aspherical surfaces, or may be arranged in two or more rows on each end surface of the lens member. Moreover, the cross-sectional shape orthogonal to the optical axis of the through-hole formed in the light shielding member may be a square, a circle, or any other shape.
Examples of the image reading device include a single-function scanner device, a multifunction device scanner device, a facsimile reading device, and a copying machine reading device.

DESCRIPTION OF SYMBOLS 1 ... Image reading apparatus, 2 ... Imaging optical apparatus, 9 ... Document, 10 ... Platen glass, 20 ... First light shielding member, 20a ... Through hole, 21 ... Second light shielding member, 21a ... Through hole, 30 ... Lens member 30a ... lens surface, 30b ... lens surface, 40 ... linear image sensor, 40a ... image surface, 201 ... through hole, 211 ... through hole, 211a ... opening, 211b ... opening, G1 ... ghost ray, G2 ... ghost ray, G3 ... Ghost rays

Claims (7)

A plurality of lens surfaces respectively connecting the erecting equal-magnification image of the target object to a predetermined image plane on the target object side and the image plane side; and
A light-shielding member that is disposed on each of the object side and the image plane side of the lens member, and has a plurality of through-holes through which optical axes of the lens surfaces different from each other are formed;
With
The through hole on the image plane side is a target beam passing through the through hole on the object side formed on the optical axis passing through the through hole and the outer periphery of the lens surface on the image plane side having the optical axis. And the intersection of the ghost rays that are not the target rays passing through the outer periphery of the lens surface on the image plane side having the optical axis, and further away from the lens surface by a predetermined margin distance from the intersection farthest from the lens surface Having an opening on the lens surface side at a position,
Imaging optical device. The width of the bundle of target rays at the position is the width of the opening of the through hole on the lens surface side,
The imaging optical device according to claim 1. The ghost light beam includes a light beam that has passed through the through hole adjacent to the through hole on the object side through which the target light beam passes through the same lens surface on the image plane side.
The imaging optical apparatus according to claim 1 or 2. The ghost ray includes a ray reflected by an inner wall surface of the through hole on the object side through which the target ray passing through the same lens surface on the image plane side passes.
The imaging optical apparatus according to any one of claims 1 to 3. The width of the through hole on the image plane side is wider in the image plane direction than the bundle of target beams that have passed through the opening on the lens plane side.
The imaging optical apparatus according to claim 1. An imaging optical device according to any one of claims 1 to 5,
An image sensor having the image plane as a light-receiving surface;
A contact-type image sensor module. An imaging optical device according to any one of claims 1 to 5,
An image sensor having the image plane as a light-receiving surface;
A positioning member for positioning a document with respect to the imaging optical device;
An image reading apparatus comprising:

Images