Imaging device

Abstract

To provide an imaging apparatus that can prevent the shift of a focal position due to a change in temperature, while ensuring waterproofness.SOLUTION: An imaging apparatus (1) has: a sensor unit (5) that has an image pickup device (5a); a lens unit (30) that has a plurality of lenses (7) and a lens frame (3) holding the plurality of lenses; a housing (2) that holds the sensor unit and the lens unit; a connection part (4) that connects the lens frame and the housing to each other; a hold-down ring (8) that covers part of a first lens (7a) arranged on the most object side of the plurality of lenses; and an elastic member (9b) that is arranged between the first lens and the hold-down ring. The coefficient of thermal expansion of the connection part is larger than the coefficient of thermal expansion of the housing and the coefficient of thermal expansion of the lens frame. A connection position (P1) of the connection part and the lens frame is arranged closer to an image side than a connection position (P2) of the housing and the connection part and the position (P3) of a first lens holding part (3c) of the lens frame.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an imaging device. [Background technology]

[0002] Imaging devices used in outdoor environments, such as in-vehicle cameras and surveillance cameras, require improved environmental resistance, including waterproofing. Patent Document 1 discloses an optical unit that ensures waterproofing by sandwiching a sealing member between the lens and a fixing part that fixes the lens inside the lens barrel from the object side.

[0003] On the other hand, to improve environmental resistance, it is necessary to compensate for changes in back focus caused by changes in ambient temperature. Patent Document 2 discloses an imaging device in which an inner part where a lens unit is attached is connected to an outer part provided with a reference surface that fixes the positional relationship with the image sensor via a connecting part. As a result, the connecting part expands and contracts in response to changes in ambient temperature, allowing the lens unit to move closer or farther from the image sensor, thereby compensating for changes in back focus. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6054720 [Patent Document 2] Patent No. 6391122 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the imaging device disclosed in Patent Document 2, the position of the lens unit in the optical axis direction changes due to temperature changes. In this case, if waterproofing is ensured by crushing and clamping the sealing member disposed between the lens and the fixed part, as disclosed in Patent Document 1, the amount of crushing of the sealing member may decrease, resulting in a decrease in waterproofing.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an imaging device that is capable of suppressing shifts in focus due to temperature changes while ensuring waterproofing. [Means for solving the problem]

[0007] An imaging device according to one aspect of the present invention includes a sensor unit having an imaging element, a lens unit having a plurality of lenses and a lens frame for holding the plurality of lenses, a housing for holding the sensor unit and the lens unit, a connecting portion for connecting the lens frame to the housing, a press ring for covering a portion of a first lens of the plurality of lenses that is arranged closest to the object, and an elastic member arranged between the first lens and the press ring, wherein the thermal expansion coefficient of the connecting portion is greater than the thermal expansion coefficient of the housing and the thermal expansion coefficient of the lens frame, and the lens frame has a first lens holding portion for holding the first lens, and a connecting position between the connecting portion and the lens frame is arranged closer to the image side than the connecting position between the housing and the connecting portion and the position of the first lens holding portion. The housing has a sensor unit holder that holds the sensor unit, and when temperature changes, a position change amount of the first lens in the optical axis direction based on a position of the sensor unit holder is smaller than a position change amount of at least one lens of the plurality of lenses other than the first lens in the optical axis direction. .

[0008] Other objects and features of the present invention are illustrated in the following examples. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an imaging device that can suppress shifts in focus due to temperature changes while ensuring waterproofing. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of an imaging device according to a first embodiment. [Figure 2] FIG. 1 is an exploded perspective view of an imaging device according to a first embodiment. [Figure 3] 1 is a cross-sectional view of an imaging device according to a first embodiment. [Figure 4] FIG. 10 is an enlarged cross-sectional view of an imaging device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0012] (First embodiment) First, an imaging device according to a first embodiment of the present invention will be described with reference to Fig. 1 and Figs. 2(A) and (B). Fig. 1 is a cross-sectional view of imaging device 1 according to this embodiment. Fig. 2(A) is an exploded perspective view of imaging device 1 as seen from the object side, and Fig. 2(B) is an exploded perspective view of imaging device 1 as seen from the image side. The imaging device 1 according to this embodiment can be applied to, but is not limited to, an in-vehicle camera, a surveillance camera, a network camera, or the like.

[0013] The housing 2 has an inner diameter threaded portion 2a, an outer diameter threaded portion 2b, and a sensor unit holding portion 2c. The sensor unit 5 has an imaging element 5a such as a CMOS sensor and a sensor plate 5b. The imaging element 5a is held to the sensor plate 5b with a UV adhesive or the like. The sensor unit 5 is attached to the sensor unit holding portion 2c of the housing 2 and fixed with screws 6.

[0014] The lens unit 30 includes a plurality of lenses 7 constituting an imaging optical system and a lens frame 3 for holding the plurality of lenses 7, and is disposed inside the housing 2. In this embodiment, the lenses 7 are composed of three lenses: a first lens 7a, a second lens 7b, and a third lens 7c, but this is not limiting. The first lens 7a is the lens of the plurality of lenses 7 that is positioned closest to the object. The lens frame 3 includes an outer thread portion 3a, a first lens holder 3c, a second lens holder 3d, and a third lens holder 3e. The lenses 7 are held inside the lens frame 3. The first lens 7a is held in contact with the first lens holder 3c. The second lens 7b is held in contact with the second lens holder 3d. The third lens 7c is held in contact with the third lens holder 3e. As a result, the positions of the first lens 7a, second lens 7b, and third lens 7c in the optical axis direction are determined by the lens frame 3.

[0015] The connecting part 4 has an inner diameter threaded portion 4a and an outer diameter threaded portion 4b. The connecting part 4 is disposed outside the lens unit 30 and inside the housing 2. The inner diameter threaded portion 2a of the housing 2 and the outer diameter threaded portion 4b of the connecting part 4 are threadedly engaged with each other, thereby holding (connecting) the connecting part 4 to the housing 2. Furthermore, the inner diameter threaded portion 4a of the connecting part 4 and the outer diameter threaded portion 3a of the lens frame 3 are threadedly engaged with each other, thereby holding (connecting) the lens unit 30 to the connecting part 4.

[0016] Next, the waterproof structure of the imaging device 1 will be described. The press ring 8 is a flange portion that covers a portion of the first lens 7a and has an inner diameter thread portion 8a, an abutment surface 8b, and an inner diameter portion 8c. The second elastic body (elastic member) 9b is sandwiched between the abutment surface 8b of the press ring 8 and the first lens 7a. The abutment surface 8b of the press ring 8 abuts against the second elastic body 9b. The first elastic body (elastic member) 9a is housed in the groove portion 2e of the housing 2. The first elastic body 9a and the second elastic body 9b are each, for example, annular O-rings. The first elastic body 9a is housed in the groove portion 2e around the optical axis OA. The second elastic body 9b abuts against the first lens 7a around the optical axis OA. The first elastic body 9a is clamped between the inner diameter portion 8c of the pressure ring 8 and the groove portion 2e of the housing 2, and the inner diameter threaded portion 8a of the pressure ring 8 is screwed into the outer diameter threaded portion 2b of the housing 2, thereby holding the pressure ring 8 in place in the housing 2.

[0017] With this configuration, the first elastic body 9a and the second elastic body 9b are clamped while being crushed. As a result, the gap between the retaining ring 8 and the first lens 7a and the gap between the retaining ring 8 and the housing 2 are sealed, preventing water from entering the lens unit 30 and the sensor unit 5. With this waterproof configuration, waterproofing can be ensured without providing a protective window for sealing or the like in front of the first lens 7a (on the object side). This makes it possible to achieve a compact imaging device 1.

[0018] Next, we will explain focus correction due to temperature changes in the imaging device 1. The screw joint (connection position P1) between the connecting portion 4 and the lens frame 3 of the imaging device 1 is located closer to the image side (image sensor side) than the screw joint (connection position P2) between the housing 2 and the connecting portion 4 and position P3 of the first lens holding portion 3c that holds the first lens 7a of the lens frame 3. The thermal expansion coefficient of the connecting portion 4 is greater than the thermal expansion coefficients of the housing 2 and the lens frame 3.

[0019] Here, an example will be described in which the ambient temperature rises. When the temperature of lens 7 rises in accordance with the ambient temperature, changes in the refractive index of lens 7 and changes in its characteristics, such as thermal deformation, occur, causing the imaging position of lens 7 to shift away from image sensor 5a toward the object side. When the temperature rises further, housing 2 thermally expands in a direction extending toward the object side based on sensor unit holding portion 2c, and similarly, lens frame 3 thermally expands in a direction extending toward the object side based on the screw engagement position between connecting portion 4 and lens frame 3. As a result, the imaging position of lens 7 shifts away from image sensor 5a toward the object side.

[0020] On the other hand, when the temperature rises, the connecting portion 4 thermally expands in the direction extending toward the image side based on the screwed position of the connecting portion 4 and the housing 2. The operation of the connecting portion 4 changes the characteristics of the lens 7 and the image sensor 5 due to the thermal expansion of the housing 2 and the lens 7. a This allows compensation for the change in the image formation position in the direction away from the image sensor 5 toward the object side. a The positions of the two can be matched within the range of the depth of focus, making it possible to maintain good image quality without blurring.

[0021] Next, we will explain how the position of the first lens 7a of the imaging device 1 changes in the direction along the optical axis OA (optical axis direction) when the temperature changes. When the sensor unit holding portion 2c of the housing 2 is used as a reference, the amount of position change of the first lens 7a in the optical axis direction when the temperature changes is calculated by multiplying the amount of temperature change by the position change coefficient expressed by the following equation (1).

[0022] |L1×α1+L3×α3-L2×α2| …(1) In formula (1), L1 is the distance in the optical axis direction from the position of the sensor unit holding portion 2c of the housing 2 to the screw-connecting portion (connection position P2) between the housing 2 and the connecting portion 4. L2 is the distance in the optical axis direction from the screw-connecting portion (connection position P1) between the connecting portion 4 and the lens frame 3 to the screw-connecting portion (connection position P2) between the housing 2 and the connecting portion 4. L3 is the distance in the optical axis direction from the screw-connecting portion (connection position P1) between the connecting portion 4 and the lens frame 3 to the position P3 of the first lens holding portion 3c of the lens frame 3. α1 is the thermal expansion coefficient of the housing 2. α2 is the thermal expansion coefficient of the connecting portion 4. α3 is the thermal expansion coefficient of the lens frame 3.

[0023] The smaller the position change coefficient calculated by equation (1), the smaller the amount of position change in the optical axis direction of the first lens 7a due to temperature changes. For example, it is preferable that the position change coefficient expressed by equation (1) is 0.1 or less (satisfying the condition |L1×α1+L3×α3+L2×α2|≦0.1). In this case, the amount of position change in the optical axis direction of the first lens 7a due to a temperature change of 50°C is 5 μm or less. As a result, the amount of change in the amount of crushing of the second elastic body 9b due to temperature changes is also 5 μm or less.

[0024] Here, L4 is the distance in the optical axis direction from the screw-engagement portion (connection position P1) between the connecting portion 4 and the lens frame 3 to the position P4 of the second lens holder 3d of the lens frame 3. Also, L5 is the distance in the optical axis direction from the screw-engagement portion (connection position P1) between the connecting portion 4 and the lens frame 3 to the position (P5) of the third lens holder 3e of the lens frame 3. In this case, the position change coefficient of the second lens 7b in the optical axis direction due to temperature changes is |L1×α1+L4×α3-L2×α2|, and the position change coefficient of the third lens 7c in the optical axis direction due to temperature changes is |L1×α1+L5×α3-L2×α2|. In the imaging device 1, distances L4 and L5 are shorter than distance L3, so |L1×α1+L4×α3-L2×α2| and |L1×α1+L5×α3-L2×α2| are greater than |L1×α1+L3×α3-L2×α2|. In this way, when the temperature changes, the amount of positional change in the optical axis direction of the first lens 7a is smaller than the amount of positional change in the optical axis direction of the second lens 7b and the third lens 7c (at least one lens other than the first lens 7a) based on the position of the sensor unit holding portion 2c.

[0025] Preferably, the absolute value of the sensitivity of the first lens 7a is 0.5 or less. Here, sensitivity corresponds to the ratio between the amount of change in position of the first lens 7a in the optical axis direction and the amount of change in position of the imaging position in the optical axis direction. For example, if the sensitivity of the first lens 7a is 0.4, when the first lens 7a moves 1 mm in the optical axis direction, the imaging position of the lens 7 moves 0.4 mm in the optical axis direction. The total sensitivity of all lenses constituting the lens unit 30 is 1. For example, if the sensitivity of the first lens 7a is 0.4, the total sensitivity of the second lens 7b and the third lens 7c is 0.6.

[0026] Even with temperature changes, the first lens 7a only changes its position in the optical axis direction relative to the sensor unit holder 2c of the housing 2, resulting in a small change in the imaging position. If the sensitivity of the first lens 7a is high, the total sensitivity of the other lenses is small. Therefore, to compensate for temperature changes in the focus position, the other lenses must be significantly displaced in the optical axis direction, requiring a large amount of space. Therefore, by setting the sensitivity of the first lens 7a to 0.5 or less, the total sensitivity of the other lenses becomes greater than 0.5. This reduces the amount of change in the position of lenses other than the first lens 7a in the optical axis direction required to compensate for temperature changes in the focus position, thereby enabling the imaging device 1 to be made more compact.

[0027] Next, with reference to Fig. 3, the amount of position change in the optical axis direction due to temperature change of the contact surface 8b of the press ring 8 of the imaging device 1 in this embodiment will be described. Fig. 3 is a cross-sectional view of the imaging device 1. If the amount of position change in the optical axis direction due to temperature change of the contact surface 8b of the press ring 8 is small, the change in the amount of crushing of the second elastic body 9b will be small even with temperature changes, and waterproofing can be maintained. Using the sensor unit holding portion 2c of the housing 2 as a reference, the amount of position change in the optical axis direction of the contact surface 8b of the press ring 8 due to temperature changes is calculated by multiplying the amount of temperature change by the position change coefficient expressed by the following equation (2).

[0028] |L6×α1+L7×α4| …(2) In equation (2), L6 is the distance in the optical axis direction from position P6 of sensor unit holding portion 2c of housing 2 to the screw-connection portion (connection position P7) between presser ring 8 and housing 2. L7 is the distance in the optical axis direction from the screw-connection portion (connection position P7) between presser ring 8 and housing 2 to position P8 of the abutment surface 8b of presser ring 8. α4 is the thermal expansion coefficient of presser ring 8.

[0029] The smaller the value of formula (2), the smaller the amount of positional change in the optical axis direction of the contact surface 8b of the press ring 8 due to temperature changes. For example, it is preferable to configure the lens so that the positional change coefficient expressed by formula (2) is 0.5 or less (satisfying the condition |L6×α1+L7×α4|≦0.5). In this case, the amount of positional change in the optical axis direction of the contact surface 8b of the press ring 8 due to a temperature change of 50°C (the amount of positional change in the optical axis direction of the first lens 7a) is 25 μm or less. As a result, the amount of change in the amount of crushing of the second elastic body 9b due to temperature changes is also 25 μm or less.

[0030] Table 1 shows the characteristics of each part of the imaging device 1 in this embodiment. As shown in Table 1, the housing 2 is made of aluminum, and the distance L1 in the optical axis direction from the sensor unit holding portion 2C of the housing 2 to the screw-connecting portion between the housing 2 and the connecting portion 4 is 20 mm. Also, the distance L6 in the optical axis direction from the sensor unit holding portion 2C of the housing 2 to the screw-connecting portion between the presser ring 8 and the housing 2 is 21.5 mm.

[0031] The connecting portion 4 is made of polycarbonate, and the distance L2 in the optical axis direction from the screw joint between the housing 2 and the connecting portion 4 to the screw joint between the connecting portion 4 and the lens frame 3 is 10 mm. The lens frame 3 is made of glass fiber-reinforced polycarbonate, and the distance L3 in the optical axis direction from the screw joint between the connecting portion 4 and the lens frame 3 to the first lens holder 3c of the lens frame 3 is 15 mm. The distance L4 in the optical axis direction from the screw joint between the connecting portion 4 and the lens frame 3 to the second lens holder 3d of the lens frame 3 is 6 mm. The distance L5 in the optical axis direction from the screw joint between the connecting portion 4 and the lens frame 3 to the third lens holder 3e of the lens frame 3 is 2 mm. The retaining ring 8 is made of aluminum, and the distance L7 in the optical axis direction from the screw joint between the retaining ring 8 and the housing 2 to the abutment surface 8b of the retaining ring 8 is 1.5 mm.

[0032] [Table 1]

[0033] The position change coefficient in the optical axis direction of first lens 7a due to temperature change is |L1×α1+L3×α3-L2×α2|=0.095, and the position change amount in the optical axis direction of first lens 7a due to a temperature change of 50° C. is 4.75 μm. The change amount of crushing of second elastic body 9b due to a temperature change of 50° C. is also 4.75 μm or less.

[0034] Similarly, the position change coefficient of the second lens 7b in the optical axis direction with temperature change is |L1×α1+L4×α3-L2×α2|=0.13, and the position change amount of the second lens 7b in the optical axis direction with a temperature change of 50°C is 6.5 μm. Furthermore, the position change coefficient of the third lens 7c in the optical axis direction with temperature change is |L1×α1+L5×α3-L2×α2|=0.23, and the position change amount of the third lens 7c in the optical axis direction with a temperature change of 50°C is 11.5 μm. Therefore, the position change amount of the first lens 7a in the optical axis direction with respect to the sensor unit holder 2c with temperature change is smaller than that of the second lens 7b and the third lens 7c.

[0035] Furthermore, the coefficient of positional change in the optical axis direction of the contact surface 8b of the presser ring 8 due to temperature change is |L6×α1+L7×α4|=0.483, and the amount of positional change in the optical axis direction of the contact surface 8b of the presser ring 8 due to a temperature change of 50° C. is 24.15 μm. As a result, the amount of change in the amount of crushing of the second elastic body 9b due to temperature change is also 24.15 μm or less.

[0036] (Second embodiment) Next, an imaging device according to a second embodiment of the present invention will be described with reference to FIG. 4. FIG. 4 is an enlarged cross-sectional view of an imaging device 1a according to this embodiment. In this embodiment, a correction member 10 is disposed between the first lens 7a and the second elastic body 9b. The correction member 10 is sandwiched between the first lens 7a and the second elastic body 9b. The correction member 10 has an annular shape and contacts the first lens 7a around the entire circumference centered on the optical axis OA. The thickness of the correction member 10 in the optical axis direction changes due to thermal expansion caused by temperature changes. This further reduces the amount of deformation of the second elastic body 9b caused by temperature changes, regardless of the position of the first lens 7a in the optical axis direction. This makes it possible to maintain waterproofing even with temperature changes. The correction member 10 may also be disposed between the contact surface 8b of the press ring 8 and the second elastic body 9b.

[0037] According to each embodiment, it is possible to provide an imaging device that can suppress shifts in focus due to temperature changes while ensuring waterproofing.

[0038] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0039] 1. Imaging device 2. Case 3 Lens frame 3c First lens holder 4 Connecting part 5 Sensor Unit 5a Image sensor 7 Lens (imaging optical system) 7a First lens 8 Presser foot ring 9b Second elastic body (elastic member) 30 Lens unit P1 Connection position between the connecting part and the lens frame P2 Connection position between the housing and the connecting part P3 Position of the first lens holder

Claims

1. a sensor unit having an imaging element; a lens unit having a plurality of lenses and a lens frame for holding the plurality of lenses; a housing for holding the sensor unit and the lens unit; a connecting portion that connects the lens frame and the housing; a press ring that covers a part of a first lens that is disposed closest to the object side among the plurality of lenses; an elastic member disposed between the first lens and the presser ring, a thermal expansion coefficient of the connecting portion is greater than a thermal expansion coefficient of the housing and a thermal expansion coefficient of the lens frame; the lens frame has a first lens holding portion that holds the first lens, a connection position between the connecting portion and the lens frame is disposed closer to the image side than a connection position between the housing and the connecting portion and a position of the first lens holding portion; the housing has a sensor unit holding portion that holds the sensor unit, An imaging device characterized in that, when temperature changes, the amount of position change in the optical axis direction of the first lens, based on the position of the sensor unit holding portion, is smaller than the amount of position change in the optical axis direction of at least one lens among the plurality of lenses excluding the first lens.

2. When the distance in the optical axis direction from the position of the sensor unit holding portion to the connection position between the housing and the connecting portion is L1, the distance in the optical axis direction from the connection position between the connecting portion and the lens frame to the connection position between the housing and the connecting portion is L2, the distance in the optical axis direction from the connection position between the connecting portion and the lens frame to the position of the first lens holding portion of the lens frame is L3, the thermal expansion coefficient of the housing is α1, the thermal expansion coefficient of the connecting portion is α2, and the thermal expansion coefficient of the lens frame is α3, |L1×α1+L3×α3+L2×α2|≦0.1 2. The imaging device according to claim 1, wherein the following condition is satisfied:

3. Let L6 be the distance in the optical axis direction from the position of the sensor unit holding portion to the connection position between the presser ring and the housing, L7 be the distance in the optical axis direction from the connection position between the presser ring and the housing to the position of the abutment surface of the presser ring, α1 be the thermal expansion coefficient of the housing, and α4 be the thermal expansion coefficient of the presser ring. |L6×α1+L7×α4|≦0.5 3. The imaging device according to claim 1, wherein the following condition is satisfied:

4. 4. The imaging device according to claim 1, wherein a ratio between a positional change amount of the first lens in the optical axis direction and a positional change amount of the imaging position in the optical axis direction is 0.5 or less.

5. 5. The imaging device according to claim 1, wherein the elastic member has an annular shape and is in contact with the first lens around the entire circumference of the annular member centered on the optical axis.

Images