Camera unit

In a camera unit having a lens and an imaging device, the imaging device is fixed by means of a base plate, an elastic material, and a printed circuit board. The imaging device abuts on a first plane of the base plate, and the elastic material is sandwiched between the printed circuit board and a second plane opposite to the first plane of the base plate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to image recognition systems typified by in-car cameras.

2. Background Art

Retention structures of imaging devices built into imaging apparatuses such as video cameras are typically obtained by bonding with an adhesive. Specifically, an imaging device is fixedly attached to a board serving as a positioning reference for assembly, in a constant relative position. After the board is inserted into and positioned within a camera housing, it is fastened with screws and the like and retained therein. For fixation of such an imaging device, a technique using an adhesive is known (see Reference 1: JP Patent Publication (Kokai) No. 2006-094444 A). There have also been proposed methods of determining the position of an imaging device with high accuracy while reducing the number of component parts of an imaging recognition system. For example, there is known a technique of mounting a semiconductor chip of an imaging device on an attachment board and determining the position of the main body of the imaging device with a positioning means provided on the attachment board (see Reference 2: JP Patent Publication (Kokai) No. 2002-9264 A). Further, there is also known a technique of forming a package of an imaging device in an irregular shape and providing the package with notches so that such notches can be used as positioning references (see Reference 3: JP Patent Publication (Kokai) No. 63-316572 A).

SUMMARY OF THE INVENTION

However, References 1 to 3 are problematic in that in a use environment of an image processing system in which temperature fluctuation or vibration occurs, it is highly probable that the subject of image recognition would not be imaged accurately because the relative position of an imaging device and a lens could be changed due to, for example, thermal stress resulting from a difference in the coefficient of linear expansion between a structural member that abuts on the imaging device and an adhesive and between the adhesive and the imaging device, stress resulting from vibration, or peeling of the adhesive resulting from deterioration of such adhesive.

In view of the foregoing, it is an object of the present invention to provide a camera unit that can accurately image an image recognition subject even in a use environment in which temperature fluctuation or vibration occurs.

One aspect of the present invention that is desirable for solving the aforementioned problems is as follows.

In a camera unit having a lens and an imaging device, the imaging device is fixed by means of a base plate, an elastic material, and a printed circuit board.

According to the present invention, a camera unit can be provided that can accurately image an image recognition subject even in a use environment in which temperature fluctuation or vibration occurs.

DESCRIPTION OF SYMBOLS

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1illustrates a layout of a camera unit.

This camera unit includes an imaging device (CCD)1, a base plate2, an elastic material3, a printed circuit board4, solder5, and a lens6. The imaging device1and the lens6are positioned a focal length of ƒ apart from each other.

A lead1-bmade of metal extends from a package1-aof the imaging device1, and the imaging device1abuts on the base plate2. The elastic material3is sandwiched between the printed circuit board and a plane on the opposite side of the base plate2on which the imaging element1abuts. As shown inFIG. 1, the imaging device1, the base plate2, the elastic material3, and the printed circuit board4are fixed with the solder5. With such a structure, the positions of the base plate2and the lens6can be fixed without being influenced by temperature changes. Further, the reliability of the camera unit can be improved and a more stable focus state can be provided.

When the elastic body3is not provided, stress could be applied to the solder5, resulting in failure as shown inFIG. 2A, due to expansion or shrinkage of each member resulting from a difference in the coefficient of linear expansion, or the distance between the imaging device1and the lens6could become too short as shown inFIG. 2Bas a result of the imaging device1being located at a distance from the base plate2, in which case an out-of-focus image would result, for example.

Considered now is a case in which aluminum (coefficient of linear expansion α: 20e-6) is used as the material of the base plate2and 42 ALLOY (coefficient of linear expansion α: 5e-6) is used as the material of the lead1-bof the imaging device1. In this case, the coefficient of linear expansion of the base plate2is four times that of the lead1-bof the imaging device1. In order to reduce adverse effect of heat, the base plate2and the lead1-bof the imaging device1are desirably formed of the same material. Note that “e” is the natural logarithm.

In practice, at high temperatures, when the lead1-bof the imaging device1expands by 10 μm, the base plate2will expand by 40 μm. However, such difference in expansion will absorbed by the elastic material3.

At low temperatures, when the lead1-bof the imaging device1shrinks by 10 μm, the base plate2will shrink by 40 μm. However, a gap of 30 μm generated by such shrinkage will be absorbed by the elastic material3pulling the imaging device1. For the elastic material3, a molding of silicone rubber with properties that will hardly change at either high temperatures or low temperatures, a plate spring made of a metal material, or the like can be used. With the aforementioned structures, a decrease in reliability or function resulting from thermal fluctuation can be suppressed.

FIG. 3illustrates a specific assembling method of the present structure.

First, the imaging device1is fixed on the base plate2. The base plate2has a reference plane on which the position of the imaging device1is to be fixed. Next, the base plate2on which each imaging device1is fixed is flipped, and the elastic body3is mounted thereon. Next, the printed circuit board4is mounted such that the elastic body3is sandwiched between the printed circuit board4and the base plate2. Then, bonding of the solder5is performed in a condition in which the printed circuit board4is pressed to a prescribed extent. The prescribed extent is determined in consideration of variations in shape, elastic modulus, compression set, and the like of the elastic body3.

When cylindrical silicone rubber measuring 4.5 mm in diameter and 1.5 mm in height is used for the elastic body3, the prescribed extent of compression will be 0.3 mm.

When silicone rubber or the like is used for the elastic body3, such silicone rubber is preferably not milky translucent but is colored. When the color difference between the elastic body3and the base plate2is set to be larger than a predetermined value, failure of mounting can be avoided. Such predetermined value can be determined in any preferred way.

In order for the elastic body3to pull the imaging device1with stability, it is necessary that the center position of the imaging device1coincide with the center position of the elastic body3. To this end, the elastic body3is preferably mounted after providing a recess portion in the base plate2to serve as a positioning portion. In such case, the shape of the recess portion is desirably cylindrical rather than rectangular so that operation failure such that the elastic body3becomes located upon the positioning portion as shown inFIG. 4Awould be avoided.

As described above, according to the present embodiment, an elastic body is provided between a printed circuit board and a base plate, and an imaging device is configured to be constantly pressed against a reference plane provided on a structural member (i.e., the base plate) with the use of the reaction force of the elastic body, whereby it becomes possible to maintain the state of abutment of the imaging device on the structural member against expansion or shrinkage of the structural member resulting from temperature fluctuation. In addition, even when a gap is instantaneously produced at a portion at which the imaging device abuts on the reference plane due to a significant vibration or shock, the state of abutment will be automatically restored by the reaction force of the elastic body.

Further, when a structure is employed in which an outline reference plane of the imaging device is pressed against a positioning reference plane within a camera with the use of the reaction force of an elastic body, it would be possible, even when the constituent member of the reference plane within the camera is subjected to repeated stress by expansion or shrinkage resulting from thermal fluctuation or by vibration in the use environment, to maintain the imaging device in a state in which it is constantly pressed against the reference plane, to maintain the mounting position of the imaging device with high accuracy, to reduce stress on the leads of the imaging device as well as the solder portion, which could be caused by aging, and thereby to maintain a favorable state.