JP2010130296A - Image reading device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader capable of suppressing deterioration in the image quality of an image read, while attaining space saving. <P>SOLUTION: The image reading device is provided with an image reading unit 50, which corrects the displacement between an image forming position of a lamination lens 61 and the light-receiving surface of a solid-state image pickup device 70 in the optical axis direction resulting from temperature rise in a machine where the image reading unit 50 includes: a lamination member 91, constituted by adhering a plate-like member of a substrate 80 and a back plate 90 having different linear expansion coefficients; and a holding part 51a, which holds the lamination member 91 to a base 51 at first and second holding positions located, by sandwiching the light axis in a state where a principal plane of the lamination member 91 is substantially perpendicular to the optical axis, and the size relation of the thermal expansion coefficients of the substrate 80 and the back plate 90 is determined so that the lamination member curves in the direction of alleviating the displacement amount in the optical axis direction, according to the rise in the temperature of the image forming position and the light-receiving surface of the solid-state image pickup device 70. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image reading apparatus that receives reflected light from a document surface on a light receiving surface of a fixed imaging element via an imaging lens to generate image data.

Image readers used in copiers and facsimile machines irradiate light from an exposure lamp onto a document and receive the reflected light on a light receiving surface of a solid-state image sensor such as a CCD (Charge Coupled Device) through an imaging lens. Then, the image data of the original is generated by performing photoelectric conversion and extracting the signal.
In the image reading apparatus having such a configuration, the temperature inside the apparatus is likely to rise due to the heat generated from the exposure lamp and the solid-state imaging device.

When the temperature inside the device rises, the distance in the optical axis direction between the imaging lens and the solid-state image sensor fluctuates due to thermal expansion of the imaging lens and the base that holds the solid-state image sensor, or the imaging lens due to the influence of heat. The focal length of the imaging lens fluctuates due to a change in the refractive index of the lens.
Due to this variation, a deviation (hereinafter referred to as “imaging position deviation”) occurs between the imaging position of the image formed by the imaging lens and the position of the light receiving surface of the solid-state imaging device, and this deviation amount is the image quality of the read image. Cause deterioration.

As a technique for preventing an imaging position shift due to the temperature rise, Patent Document 1 discloses that an imaging lens 1004 is fixed on a base 1001 and a solid-state image sensor 1003 is an L-shaped as shown in FIG. It is held on the base 1001 through a holding member 1002. An L-shaped horizontal portion 1002a of the holding member 1002 extends in a direction opposite to the imaging lens 1004, and is coupled to the base 1001 at an engaging portion 1002b on the lower surface of the distal end side. Therefore, even if the base 1001 expands due to the temperature rise and the coupling position with the holding member 1002 is displaced in the right direction in the drawing, the horizontal portion 1002a of the holding member 1002 starts from the engagement portion 1002b as the left side of the drawing. The distance between the solid-state imaging device 1003 and the imaging lens 1004 is suppressed and the imaging position deviation is reduced.
Japanese Patent Laid-Open No. 2007-148047

However, in the image reading apparatus disclosed in Patent Document 1, it is necessary to increase the length of the horizontal portion 1002a in the optical axis direction to some extent in order to cancel out the displacement in the optical axis direction due to the thermal expansion of the base 1002. There is a problem that must be large.
The present invention has been made in view of the above-described problems, and an object thereof is to provide an image reading apparatus capable of suppressing deterioration in image quality of a read image while saving space.

  In order to achieve the above object, an image reading apparatus according to the present invention generates reflected image light from a document surface by a light receiving surface of a solid-state image sensor through an imaging lens fixed to a base. An image reading apparatus comprising: an image forming position correcting unit that corrects a positional shift in an optical axis direction between an image forming position of the image forming lens and a light receiving surface of the solid-state image pickup device due to a temperature rise in the apparatus, The imaging position correcting means includes a laminated member formed by adhering first and second plate-like members having different linear expansion coefficients, and the laminated member in a state where the main surface is substantially orthogonal to the optical axis. And holding means for holding the base via the first and second parts sandwiching the optical axis, and the solid-state image sensor on the main surface of the laminated member on the imaging lens side. Is held with its light receiving surface substantially parallel to the main surface. The magnitude relationship between the thermal expansion coefficients of the first and second plate-shaped members is that the laminated member has a positional shift amount in the optical axis direction associated with a temperature rise between the imaging position and the light receiving surface of the solid-state imaging device. It is determined to be warped in the direction of reduction.

With the above configuration, the laminated member warps in a direction that reduces the amount of deviation of the imaging position in the optical axis direction accompanying the temperature rise between the imaging position and the light receiving surface of the solid-state imaging device. The amount of displacement of the position from the light receiving surface of the solid-state image sensor is reduced, and deterioration of the image quality of the read image can be suppressed.
In addition, since the laminated member is arranged substantially orthogonal to the optical axis, it does not take up space in the optical axis direction, and appropriately determines the linear expansion coefficients of the first and second plate-like members in the laminated member. In addition, it is possible to secure a sufficient amount of warpage accompanying the temperature rise and suppress the amount of deviation of the imaging position.

The solid-state imaging device is preferably mounted on a circuit board, and the circuit board is preferably the first plate-like member.
Since the solid-state imaging device is usually mounted on a circuit board, it is not necessary to separately provide the first plate-like member, and the cost can be reduced.
Further, the direction connecting the first and second parts and the longitudinal direction of the solid-state image sensor substantially coincide, and the center of the solid-state image sensor in the longitudinal direction and the center of the first and second parts are It is desirable that the solid-state imaging device is held by the laminated member in a substantially matched state, and the lamination center is such that the longitudinal center of the solid-state imaging device exists on the optical axis of the imaging lens. It is desirable that the member is held by a holding member.

  As a result, the laminated member deforms symmetrically about the optical axis, so that the solid-state imaging device is displaced while maintaining a state substantially orthogonal to the optical axis even if the laminated member is warped. be able to.

Hereinafter, an embodiment of an image reading apparatus according to the present invention will be described by taking as an example a case where the image reading apparatus is applied to a mirror scan type image reading apparatus.
This mirror scanning method is a method of reading a document by moving a light source or a plurality of mirrors while maintaining a constant optical path length from the document surface to the imaging lens.
FIG. 1 is a diagram showing a schematic configuration of the image reading device 8.

As shown in FIG. 1, the image reading device 8 includes a document pressing plate 11 and an image reading unit 12.
The document pressing plate 11 is used to press the document placed on the machine frame of the image reading unit 12 from above, and is pivotally supported on the upper portion of the image reading unit 12 so as to be opened and closed.
The image reading unit 12 controls a mirror unit 38, a folding mirror unit 43, a drive motor M, and an image reading unit 50 in a box-shaped machine frame 32 having a platen glass 31 fitted on the upper surface. The control part 47 etc. are accommodated.

The mirror unit 38 includes a lamp 40 and a mirror 42, and the folding mirror unit 43 includes a folding mirror 44 and a folding mirror 46.
The original placed on the platen glass 31 is irradiated by the lamp 40 through the platen glass 31, and the reflected light is reflected in the horizontal direction by the mirror 42 and further reflected by the folding mirror 44 and the folding mirror 46. The light enters the reading unit 50.

When executing document reading, the mirror unit 38 is moved in the direction of arrow A in the figure by the motor M and a driving mechanism (not shown) to scan the document image.
At this time, the folding mirror unit 43 moves in the same direction as the mirror unit 38 at a half of its moving speed, so that from the document surface to the lens unit 60 in the image reading unit 50. With the optical path length kept constant, the reflected light from the document can be imaged on the light receiving surface of the solid-state image sensor 70 in the image reading unit 50.

As a scanner drive mechanism, for example, the scanner is slidably held on two or more rails arranged in parallel with the direction of arrow A, and a wire stretched on a pulley is used. A known drive mechanism is used in which a scanner is connected to a part and the wire is driven by a scanner motor M.
Reflected light from the document incident on the solid-state image sensor 70 is converted into an electrical signal, A / D converted by the control unit 47 to become a multi-value digital signal, and further processing such as shading correction, density conversion, and edge enhancement is performed. After being added, it is stored in an image memory (not shown).

The control unit 47 includes a CPU, a signal processing unit, an image memory, a ROM, a RAM, a communication interface, and the like as main components, and performs processing such as A / D conversion on the image data read by the solid-state imaging device 70. The image data is transmitted to the external device.
(Configuration of image reading unit 50)
2A is a cross-sectional view showing the configuration of the image reading unit 50 when the environmental temperature is substantially room temperature t0 (about 25 ° C.), and FIG. 2B is a horizontal cross-sectional view thereof. is there.

As shown in FIG. 2A, the image reading unit 50 includes a base 51, a lens unit 60, an image sensor unit 69, and a light shielding cover 97 that covers them.
The light shielding cover 97 is made of resin or metal having light shielding properties, and has an opening 97a on the side surface.
The lens unit 60 is formed by fixing a laminated lens 61 in which a plurality of lenses are laminated in the optical axis direction with a lens holder 62.

The lens holder 62 is fixed to the upper surface of the pedestal 62a with an adhesive or the like, and the pedestal 62a is substantially at the center in the optical axis direction (X direction) as shown in FIG. It is fixed on the base 51 by screws 68 at the sandwiched position.
The base 51 is, for example, a plate body made of metal or resin, and has a T shape in plan view (FIG. 2B).

The image sensor unit 69 includes a solid-state image sensor 70, a substrate 80 on which the solid-state image sensor 70 is mounted, and a back plate 90 joined to the back surface of the solid-state image sensor 70 with an adhesive.
The board 80 is a rectangular printed board on which electronic components such as the solid-state imaging device 70 and a memory are mounted.
The solid-state imaging device 70 is, for example, a line sensor in which photoelectric conversion elements such as CCDs are arranged in a line, the light receiving surface thereof is parallel to the main surface of the substrate 80, and the longitudinal directions of both are coincident. In such a state, the lead pin 71 is soldered and held on the substrate 80.

After mounting other necessary electronic components on the board 80 and soldering to complete the circuit board, an insulating resin adhesive (for example, an acrylic adhesive) is applied to the back surface of the back board 90. The substrates are bonded together (hereinafter, the substrate 80 and the back plate 90 are referred to as “laminated member 91”).
As shown in FIG. 2B, the laminated member 91 is parallel to the Y-axis direction, and the center in the longitudinal direction of the solid-state imaging device 70 mounted on the substrate 80 substantially coincides with the optical axis L. In this state, the base 51 is fixed by screws 95 to a pair of holding members 51a that are erected in a substantially symmetrical position across the optical axis L.

When the environmental temperature of the image reading device 8 increases, the distance L1 (FIG. 2) in the X-axis direction from the screw 68 for fixing the lens unit 60 to the holding portion 51a is changed to L2 (FIG. ))).
Further, in the lens unit 60, since the refractive index of each lens changes with temperature change, the lens holder 62 holding these lenses also changes in size due to thermal expansion. The focal length changes.

For this reason, even if it is set so that an image is formed on the light receiving surface of the solid-state image sensor 70 at the time of assembly (room temperature), if the temperature changes, the image forming position is shifted from the light receiving surface of the solid-state image sensor 70. Image position shift occurs.
The back plate 90 is provided in order to reduce such an image formation position shift, and satisfies the following requirements.

(Regarding the linear expansion coefficient of the back plate 90)
When the focal length of the lens unit 60 changes as the temperature rises and the image formation position moves by Δf in the optical axis direction, the screw 68 that fixes the lens unit 60 to the holding portion 51a in the optical axis direction. If the change in distance L is ΔL (= L2−L1) (the amount of change in the X direction is positive) and Δf−ΔL = Δd, then the value of Δd becomes the actual amount of imaging position deviation. Equivalent to.

The sign of Δd is determined for each model depending on the conditions such as the lens material and its combination, the material of the bracket 62, the material of the base 51, and the distance L1 in the optical axis direction.
(1) When Δd <0
In a model in which Δd <0, the imaging position comes before the light receiving surface of the solid-state image sensor 70, so the position of the solid-state image sensor 70 needs to be displaced in the lens unit 60 direction (X ′ direction).

In this case, the linear expansion coefficient of the back plate 90 is set to be smaller than the linear expansion coefficient of the substrate 80.
As a result, the thermal expansion amount of the substrate 80 becomes larger than the thermal expansion amount of the back plate 90, and as shown in FIG. 3B, the laminated member 91 warps so as to bulge in the X ′ direction, thereby Since it is displaced by ΔS, the image formation position shift is corrected accordingly.

  At this time, since the substrate 80 and the back plate 90 are bonded to each other with an adhesive having a predetermined elasticity even after being fixed, it is possible to absorb a minute shift generated on the bonding surface and the adhesive layer is peeled off. There is nothing to do. In addition, if the back plate 90 is too thin, it stretches following the elongation of the substrate 80, and the amount of warpage is reduced. Therefore, it is necessary to have a certain thickness and Young's modulus. Those specific ranges can be easily determined by those skilled in the art so as to satisfy the following conditional expressions.

Ideally, the absolute values of ΔS and Δd are equal over the entire temperature range. However, although it is empirically known that the absolute values of both tend to increase monotonically with temperature rise, it is difficult to always make them equal because the rates of change are different.
The image reading device is adjusted so that Δd = 0 at room temperature (20 ° C.) at the time of assembly, and the temperature inside the image reading device rises to about 60 ° C. at maximum, so that it is under a normal use environment. In the temperature range of 20 ° C. to 60 ° C., Δd may be set within the allowable range A.

That is, −A ≦ | Δd | − | ΔS | ≦ A (formula C)
It is sufficient to obtain a warping amount ΔS that satisfies the above.
The value of A is set to about 25 μm, for example. This is because almost no degradation of the image quality can be visually recognized.
As described above, the warping direction of the laminated member 91 accompanying the temperature rise is determined by the difference in the linear expansion coefficient between the substrate 80 and the back plate 90.

Further, the warpage amount ΔS is somewhat dependent on the difference in the linear expansion coefficient, but has a certain correlation with the difference in the elongation amount in the longitudinal direction of the substrate 80 and the back plate 90. This mainly depends on the pitch P1 (see FIG. 2B).
Therefore, the linear expansion coefficient and the pitch P1 of the back plate 90 are obtained in advance through experiments and simulations so as to satisfy the conditional expression C in the temperature range of 20 ° C. to 60 ° C.

At this time, as the material of the back plate 90, for example, if polycarbonate filled with a filler such as glass fiber is used, the linear expansion coefficient can be easily adjusted by changing the amount of the filler mixed.
Moreover, as long as the said conditional expression C is satisfy | filled, the material of the backplate 90 may be a metal.

Even if the conditional expression C cannot be satisfied in the entire temperature range, at least the value of the image formation position deviation Δd can be made smaller than in the conventional case, and image quality degradation can be suppressed accordingly.
Normally, since the image reading apparatus is used indoors, even if it is used in a use environment lower than room temperature (20 ° C.), it is about 10 ° C. at most. In this embodiment, the amount of contraction of the substrate 80 becomes larger than the amount of contraction of the back plate 90 even if Δd is changed to a positive value when the temperature is lower than room temperature. Since the member 91 also tends to warp in the positive direction (X direction), it also acts to cancel out Δd and can maintain good image quality.

  In addition, when the laminated member 91 is warped, the solid-state imaging device 70 may be inclined with respect to the Y axis. However, in actuality, the imaging position deviation amount Δd is about several tens of microns at the maximum, and the warping amount ΔS is also about that level. In addition, in the image reading unit 50 of the present embodiment, as described above, the image sensor unit 69 has a substantially symmetric shape in the Y-axis direction, and holds the laminated member 91 at the symmetrical position. Since 91 is deformed symmetrically in the Y-axis direction, even if the solid-state imaging device 70 is tilted due to warping of the laminated member 91, it is extremely small and has almost no influence on the image quality.

In addition, the lead pin 71 is provided at a substantially symmetrical position with respect to the center in the longitudinal direction of the solid-state imaging device 70 and is somewhat elastic because it is a metal, so that when the laminated member 91 is warped. When the solid-state image sensor 70 is held while being deformed, and the laminated member 91 returns from a warped state to a straight state, the shape returns to the original state, so that the tilt is less likely to occur.
(2) In the case of Δd> 0 In a model where Δd> 0, the imaging position exceeds the position of the light receiving surface of the solid-state image sensor 70, so the position of the solid-state image sensor 70 is opposite to the lens unit 60. It is necessary to displace in the (X direction).

In this case, the linear expansion coefficient of the back plate 90 is set to be larger than the linear expansion coefficient of the substrate 80.
As a result, the thermal expansion amount of the back plate 90 becomes larger than the thermal expansion amount of the substrate 80, and as shown in FIG. 4B, the laminated member 91 is warped so as to bulge out in the X direction, and the imaging position deviation is corrected. The solid-state imaging device 70 moves in the direction in which it is moved.

Even in this case, it is needless to say that the conditional expression C is satisfied. It can be achieved by appropriately adjusting not only the linear expansion coefficient of the back plate 90 but also the size of the pitch P1 if necessary. It is.
As described above, in the image reading unit 50 according to the present embodiment, the magnitude relationship between the thermal expansion coefficients of the substrate 80 and the back plate 90 constituting the laminated member 91 is the imaging position deviation amount, that is, the imaging position and the solid state. Since the laminated member 91 is determined to be warped in a direction to reduce the amount of positional deviation in the optical axis direction due to the temperature rise with the light receiving surface of the image sensor, the environmental temperature rises and the imaging position deviation occurs. Can fall within a predetermined range.

In addition, the laminated member 91 is arranged in a direction orthogonal to the optical axis of the lens unit 60 and can be provided in a space that originally has a margin, so that the apparatus scale is not increased, which contributes to space saving.
<Modification>
The present invention is not limited to the above-described embodiment, and the following modifications can be implemented.
(1) In the above embodiment, the laminated member 91 is directly clamped with the screw 95. In such a case, the laminated member 91 is repeatedly warped, whereby a stress fluctuation in the X-axis direction occurs in the screw 95. Since it becomes easy to loosen, you may tighten via elastic members, such as a spring washer.

In addition, since the deformation of the both end portions of the laminated member 91 is facilitated by using such an elastic member, the amount of warp ΔS of the solid-state imaging device 70 per unit temperature change can be increased.
(2) Moreover, in the said embodiment, although the both ends of the laminated member 91, ie, the thing which affixed the board | substrate 80 and the backplate 90, was hold | maintained, it is not restricted to this structure.

That is, it may be configured such that one of the substrate 80 and the back plate 90 is shortened and only the other end portions of the other are screwed.
(3) Further, in the above embodiment, the screw 95 is used to hold the laminated member 91. However, the present invention is not limited to this. For example, both ends of the laminated member 91 in the Y-axis direction are fitted and fixed. A nail-like member may be provided on the holding portion 51a.
(4) In the above embodiment, since the back plate 90 is adhered to the back surface of the substrate 80, it is desirable that the back surface of the substrate 80 be as flat as possible.

However, in reality, it is conceivable that the end of the lead pin or solder protrudes from the back surface of the substrate 80. In such a case, the back plate 90 is notched at a position corresponding to the protruding portion of the substrate 80. Perforations may be provided.
Furthermore, it is desirable that the notches and the holes are provided symmetrically with respect to the center in the Y-axis direction so that warpage is easily generated symmetrically with respect to the center.
(5) In the present embodiment, the holding portion 51a for holding the solid-state imaging device 70 is directly erected on the base 51, but is indirectly held on the base 51 via another member. It does not matter if it is made.
(6) In the above-described embodiment, the mirror scanning type image reading device 8 has been described. However, the present invention is not limited to this. For example, a single light source, an optical element such as a lens or a folding mirror, and a solid-state image sensor are provided. The image forming apparatus may be applied to a known unit scan type image reading apparatus that is housed in a housing and unitized, and is moved to read a document.
(7) Further, in the above embodiment, the description has been given of the image reading apparatus of the moving optical system that reads the image while placing the document on the platen glass and moving the folding mirror. However, the present invention is not limited to this configuration.

For example, instead of the document pressing plate, an automatic document transport device that sequentially transports the document while passing through a specific region on the platen glass is provided, and passes through the specific region without moving the light source or the folding mirror. A so-called sheet-through method of reading an image may be used.
(8) In the above embodiment, the solid-state imaging device 70 is a CCD sensor. However, the solid-state imaging device 70 is not limited to this, and other solid-state imaging devices such as a CMOS sensor may be used.
(9) Here, it goes without saying that the above embodiment and the above modification can be implemented in combination as much as possible.
(10) Further, in the above-described embodiment, the present invention has been described with respect to an image reading apparatus. However, the present invention can be applied to an image forming apparatus such as a copying machine in which such an image reading apparatus and a printer are combined. Is possible.

  The present invention is suitable as an image reading apparatus that does not cause deterioration of a read image even if the temperature inside the apparatus rises.

1 is a diagram illustrating a schematic configuration of an image reading apparatus according to an embodiment of the present invention. (A) is a cross-sectional view showing the state of the image reading unit according to the embodiment of the present invention at room temperature corresponding to the characteristic that the imaging position of the lens unit shifts to the lens unit side as the temperature rises. And (b) is a horizontal sectional view thereof. (A) is a cross-sectional view showing a state at a high temperature of the image reading unit according to the embodiment of the present invention, corresponding to the characteristic that the imaging position of the lens unit shifts to the lens unit side as the temperature rises. And (b) is a horizontal sectional view thereof. (A) is a cross-sectional view showing a state at a high temperature of the image reading unit according to the embodiment of the present invention corresponding to the characteristic that the imaging position of the lens unit moves away from the lens unit as the temperature rises. , (B) is a horizontal sectional view thereof. It is a figure which shows schematic structure of the conventional image reading unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 8 Image reading apparatus 11 Document pressing plate 12 Image reading part 31 Platen glass 32 Machine frame 38, 43 Mirror unit 40 Lamp 42, 44, 46 Mirror 47 Control part 50 Image reading unit 51 Base 51a Holding part 60 Lens unit 61 Multilayer lens 62 Lens holder 69 Image sensor unit 70 Solid-state imaging device 71 Lead pin 80 Substrate 90 Back plate 91 Laminated member 97a Opening 97 Light-shielding cover 206a Seat

Claims (4)

An image reading device that receives reflected light from a document surface on a light receiving surface of a solid-state imaging device via an imaging lens fixed to a base, and generates image data,
An imaging position correcting means for correcting a positional deviation in the optical axis direction between the imaging position of the imaging lens and the light receiving surface of the solid-state imaging device due to a temperature rise in the apparatus,
The imaging position correcting means includes
A laminated member formed by adhering first and second plate-like members having different linear expansion coefficients;
Holding means for holding the laminated member on the base via first and second parts that sandwich the optical axis in a state in which the main surface is substantially orthogonal to the optical axis;
The solid-state imaging device is held on the main surface of the laminated member on the imaging lens side in a state where the light receiving surface thereof is substantially parallel to the main surface,
The magnitude relationship between the thermal expansion coefficients of the first and second plate members reduces the amount of positional deviation in the optical axis direction when the laminated member rises in temperature between the imaging position and the light receiving surface of the solid-state imaging device. An image reading apparatus, wherein the image reading apparatus is determined so as to warp in a moving direction.   The image reading apparatus according to claim 1, wherein the solid-state imaging element is mounted on a circuit board, and the circuit board is the first plate member. The direction connecting the first and second parts and the longitudinal direction of the solid-state image sensor substantially coincide, and the center of the solid-state image sensor and the center of the first and second parts substantially coincide. 3. The image reading apparatus according to claim 1, wherein the solid-state imaging element is held by the laminated member in a state of being performed.   The image reading apparatus according to claim 3, wherein the laminated member is held by a holding member so that a longitudinal center of the solid-state imaging element exists on an optical axis of the imaging lens.

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