Image reading apparatus and assembling method

A document reading apparatus includes a sensor configured to receive light from a document, an imaging lens configured to form an image of light from the document on the sensor, a first holding member to which the imaging lens is fixed, and a second holding member to which the sensor is fixed, wherein the first holding member and the second holding member are fixed using an adhesive and solder.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image reading apparatus including an imaging unit that forms an image of light from a document, and a image sensor that receives the light from the document via the imaging unit, and a method for assembling the image reading apparatus.

2. Description of the Related Art

Conventionally, there is an image reading apparatus including an optical unit as illustrated inFIG. 10. The optical unit uses an imaging unit to form an image of light from the document on a solid-state image sensor, and thus generates image data of the document.

In general, when the image reading apparatus is assembled, optical adjustment is performed as follows.

Referring toFIG. 10, a solid-state image sensor100is mounted on a solid-state image sensor substrate101. The solid-state image sensor substrate101, on which the solid-state image sensor100has been mounted, is fixed to a substrate holding member102. An imaging unit103is fixed to an optical unit frame104. After the optical adjustment is performed, the substrate holding member102is fixed to solid-state imaging unit holding members106aand106b, which are fixed to the optical unit frame104. The position of the solid-state image sensor100with respect to the imaging unit103is adjusted in performing the optical adjustment.

More specifically, the substrate holding member102is temporarily held by an adjustment tool (not illustrated). A gap of approximately 1 mm is then formed between the substrate holding member102temporarily held by the adjustment tool and the solid-state imaging unit holding members106aand106b. The adjustment tool is then used to move the substrate holding member102, to which the solid-state image sensor100is fixed via the solid-state image sensor substrate101. The position of the solid-state image sensor100in X, Y, and θ directions is thus adjusted to adjust the focus on the solid-state image sensor100.

Adhesives are then injected to and fixated in the gap between the substrate holding member102and the solid-state imaging unit holding members106aand106bat fixed portions107a,107b,107c, and107din the adjusted position. As a result, the substrate holding member102is fixed to the optical unit frame104. In other words, the solid-state image sensor100and the imaging unit103are fixed to the optical frame unit in a focus-adjusted state. Adhesives, such as a naturally curable adhesive, an ultraviolet curable adhesive, and an instant adhesive, are used.

In recent years, the adhesive is automatically applied, and efficiency is thus improved. However, since the adhesive is made of a material such as acrylic resin and epoxy resin, there is a lack of strength.

Further, solder maybe used as a fixing member instead of the adhesive. The fixing strength of the solder is sufficient. However, soldering needs a skilled worker. For example, if a soldering iron is pressed on the substrate holding member102while soldering, the position of the substrate holding member, which is only temporarily fixed by the adjustment tool, becomes displaced. Fixing using the solder is thus inefficient.

Furthermore, when the adhesive hardens, volume contraction occurs, so that a relative distance between the solid-state image sensor100and the imaging unit103is changed. As a result, focus variation occurs before and after curing, and image degradation is generated. In recent years, an increase in the pixel number of the solid-state image sensor has made the solid state image sensor sensitive to changes in the focusing. As a result, the defocusing amount caused by the change in the volume when the adhesive hardens is not ignorable.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a document reading apparatus includes a sensor configured to receive light from a document, an imaging lens configured to form an image of light from the document on the sensor, a first holding member to which the imaging lens is fixed, and a second holding member to which the sensor is fixed, wherein the first holding member and the second holding member are fixed using an adhesive and solder.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiment of the invention will be described in detail below with reference to the drawings.

FIG. 4is a cross-sectional view illustrating an image reading apparatus according to a first exemplary embodiment of the present invention.FIG. 3is a cross-sectional view illustrating an optical unit in the image reading apparatus.FIG. 1is a perspective view illustrating a substrate holding member in the optical unit.FIG. 2is a perspective view illustrating an imaging lens holding member in the optical unit.

Referring toFIG. 4, the image reading apparatus reads a document positioned on a document positioning glass plate110by moving the optical unit in a moving direction. The optical unit is stored in a reader frame111, and a timing belt113driven by a motor moves the optical unit along a guide shaft112in the moving direction indicated by an arrow illustrated inFIG. 4.

Referring toFIG. 3, the optical unit includes an optical unit frame104, the imaging lens103, plane mirrors109a,109b,109c, and109d, and a solid-state image sensor100. The plane mirrors109a,109b,109c, and109dguide to the imaging lens103the light, which is irradiated by an illumination unit (not illustrated) and reflected on the document. The imaging lens103thus forms an image on the solid-state image sensor100. The solid-state image sensor100then generates an image signal, i.e., an electrical signal, based on the received reflected light. According to the present exemplary embodiment, a complementary metal-oxide semiconductor (CMOS) sensor is used as the solid-state image sensor which receives the reflected light from the document and generates the image signal. A charge-coupled device (CCD) sensor may also be used as the solid-state image sensor.

Referring toFIG. 1, the solid-state image sensor substrate101, on which the solid-state image sensor100is mounted, is fixed to the substrate holding member102. According to the present exemplary embodiment, the solid-state image sensor substrate101is fixed to the substrate holding member102by a screw. On the other hand, referring toFIG. 2, the imaging lens103including the lens is fixed to the imaging lens holding member105. Further, the substrate holding member102is fixed to the imaging lens holding member105, and the imaging lens holding member105is fixed to the optical unit frame. The substrate holding member102and the imaging lens holding member105are formed by bending a tinned steel plate.

When assembling, an assembling worker adjusts a positional relation between the imaging lens holding member105and the substrate holding member102so that the focus becomes adjusted. After performing the adjustment, the assembling worker fixes the substrate holding member102to the imaging lens holding member105using the adhesive and the solder. The assembling worker then fixes to the optical unit frame104the imaging lens holding member105fixed to the substrate holding member102.

The optical adjustment performed in assembling the optical unit will be described below.

In the optical adjustment, the position of the solid-state image sensor100with respect to the imaging lens103is adjusted. A gap of approximately 1 mm is formed in respective vertical and horizontal focus moving directions in a connecting portion between the imaging lens holding member105and the substrate holding member102, to allow adjustment. According to the present exemplary embodiment, an adjustment tool illustrated inFIG. 5is used to adjust the position of the substrate holding member102, to which the solid-state image sensor100is fixed, with respect to the imaging lens holding member105to which the imaging lens103is attached.

Referring toFIG. 5, an adjustment tool200includes a pedestal204, to which the imaging lens holding member105is temporarily fixed, and a stage203, to which the substrate holding member102is temporarily fixed.

More specifically, the substrate holding member102is temporarily fixed using left and right guide pins201aand201bto a clamp device202attached to the stage203. According to the present exemplary embodiment, the solid-state image sensor substrate101, on which the solid-state image sensor100is mounted, is fixed to the substrate holding member102.

The stage203adjusts the position of the substrate holding member102in the X, Y, and θ directions. By adjusting the position of the substrate holding member102in the X, Y, and θ directions using the stage203, the position of the solid-state image sensor100with respect to the imaging lens103can be adjusted so that the focus becomes adjusted.

The method for fixing to the imaging lens holding member105the substrate holding member102, on which optical adjustment has been performed, will be described below.

An automatic injector device (not illustrated) injects the adhesive to gaps as fixed portions107aand107bbetween the substrate holding member102, on which optical adjustment has been performed, and the imaging lens holding member105that are temporarily fixed to the adjustment tool200. After the adhesive has naturally hardened and reached practical strength, the worker fixes to the imaging lens holding member105the substrate holding member102using the solder at positions108aand108b, which are different from the positions in which the adhesive has been injected. The positions108aand108bbound using the solder are near positions, as the fixed portions107aand107b, bound by the adhesive, respectively, and are within a range in which the heat due to soldering is transferred.

When the solder cools down and is solidified, the binding strength reaches the same level as the binding strength of metal welding. The substrate holding member102and the imaging lens holding member105are thus directly and firmly bonded together without other members. As a result, breakage or displacement of the fixed portions due to vibration or impact can be prevented.

When soldering is performed, the substrate holding member102and the imaging lens holding member105are previously fixed to each other by the adhesive. Thus, the displacement does not occur even if the soldering iron touches the substrate holding member. In other words, the soldering efficiency is improved as compared to the conventional case where the substrate holding member102and the imaging lens holding member105are fixed using only the solder. Further, since displacement rarely occurs in the soldering, it is not necessary to firmly perform the temporary fixation of the substrate holding member. As a result, the clamp device, such as a magnet clamp which is easily attachable and detachable, may be used, so that efficiency can be further improved.

Furthermore, it is confirmed that a change in focusing before and after the adhesive has hardened can be reduced by setting a soldering bonding position near an adhesive bonding position.FIG. 6illustrates amounts of focusing position displacement when the substrate holding member102and the imaging lens holding member105are fixed to each other using the adhesive and then by soldering, after the optical adjustment is performed. Referring toFIG. 6, a vertical axis indicates an amount (μm) of displacement of the focusing position when the focusing position before the adhesion (that is, after performing the optical adjustment) is set to zero. “Adhesion” indicated on a horizontal axis is timing at which the fixation is performed using the adhesive while the focus position has been adjusted by the optical adjustment. “Soldering” indicates timing at which soldering is performed after the adhesive has fixated. “After soldering” indicates timing at which the solder has fixated. Lines No.1, No.2, No.3, No.4, No.5, No.6, No.7, No.8, and No.9each indicate results of the experiment. As illustrated inFIG. 6, the focusing position, which has been displaced due to volume contraction caused by fixation of the adhesive, can be returned towards the zero position direction by performing soldering. Further, according to the present exemplary embodiment, the focusing position displacement becomes less than or equal to ±10 μm, which is an appropriate range thereof, in all of the nine experiment results. As described above, the effect of volume contraction due to the hardening of the adhesive can be reduced by arranging the fixed portion using the solder near the fixed portion using the adhesive. It is assumed that such a phenomenon occurs as follows. The heat caused by the soldering is transferred to the fixated adhesive, and the hardened adhesive expands. An anneal effect then occurs on the hardened adhesive, and an internal distortion (residual stress) of the hardened adhesive is released, so that the focusing position, which has been displaced due to the effect of the volume contraction, returns towards the zero position direction.

Further, the solder-fixed portion acts as a ground between the substrate holding member102and the imaging lens holding member105, and may thus hold a margin with respect to static and electromagnetic interference (EMI) radiation noise.

The ultraviolet curable adhesive may be used as the adhesive. The ultraviolet curable adhesive hardens in a short time by being irradiated with the ultraviolet light, so that work time can be shortened. Further, an instant curable adhesive may be used as the adhesive. If there is a gap which cannot be reached by the ultraviolet light, or a portion which cannot be reached by the ultraviolet light due to a shadow of a shape, the substrate holding member102and the imaging lens holding member105may be fixated in a shorter time by using the instant curable adhesive instead of the ultraviolet curable adhesive.

Further, the positions and the number of the adhesive-fixed portions and the solder-fixed portions are not limited to the positions and the number illustrated inFIG. 2.

For example, as illustrated inFIG. 7, there may be four adhesive-fixed portions (107a,107b,107c, and107d) and two solder-fixed portions (108aand108b). Referring toFIG. 7, the solder-fixed portions are arranged to be approximately equidistant from the plurality of positions bound using the adhesive. In other words, the position of the solder-fixed portion108ais approximately equidistant from the adhesive-fixed portions107aand107b, and the position of the solder-fixed portion108bis approximately equidistant from the adhesive-fixed portions107cand107d. By such an arrangement, the heat caused by performing the soldering is equally transferred to the respective adhesives, so that the anneal effect on each adhesive makes the contraction amount due to the hardening uniform, and thus the change in focusing is further reduced.

Furthermore, as illustrated inFIG. 8, the worker can view from the imaging lens side of the adjustment tool the positions of the adhesive-fixed portions107a,107b,107c, and107dand the solder-fixed portions108aand108b. When performing the optical adjustment, the worker performs the adjustment while viewing from the imaging lens side. If the adhesive-fixed portions and the solder-fixed portions are arranged not to mutually become blind spots when the worker views the adjustment tool from the imaging lens side, the efficiency can be improved and failure to perform bonding may be prevented.

Moreover, as illustrated inFIG. 9, the positions of the adhesive-fixed portions107a,107b,107c, and107dand the solder-fixed portions108aand108bare arranged approximately on an ellipse centered on an optical axis of the lens in the imaging lens103. According to the above-described exemplary embodiment, the amount of displacement of the focus position due to the volume contraction when the adhesive hardens can be reduced. However, the amount of displacement cannot be reduced to zero. To solve such a problem, if the positions of the adhesive-fixed portions and the solder-fixed portions are arranged as illustrated inFIG. 9, the following may be achieved. The amount of displacement due to contraction, which cannot be reduced according to the above-described exemplary embodiment, becomes uniform in a main scanning direction or a sub-scanning direction with respect to the imaging lens. In other words, a failure such as a one-sided blur can be prevented. The positions of the adhesive-fixed portions and the solder-fixed portions do not have to be arranged approximately on an ellipse, but may be arranged approximately on a circle.

This application claims the benefit of Japanese Patent Application No. 2012-123494 filed May 30, 2012, which is hereby incorporated by reference herein in its entirety.