Lens unit and camera module

Abstract

To provide a lens with a film which prevents an antireflection film on a lens surface from being adversely affected by the heat of a heater for heating the lens, and to provide a lens unit and a camera module.SOLUTION: A lens unit 11 includes a lens 13 with a film which is provided at an end on an object side of a lens barrel 12 and has an antireflection film 30 formed on a surface thereof. The antireflection film 30 is formed by alternately laminating a first film formed of a first material having a first refractive index and a second film formed of a second material having a second refractive index higher than the first refractive index, and the first material and the second material have thermal shock resistance of 500 °C or higher.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a lens unit and a camera module, and more particularly to a lens unit and a camera module that can be provided in an in-vehicle camera mounted on a vehicle such as an automobile. [Background technology]

[0002] In recent years, automobiles have been equipped with on-board cameras to assist with parking and prevent collisions through image recognition, and attempts have also been made to apply these to autonomous driving.The camera module of such on-board cameras generally includes a lens unit having a lens group consisting of multiple lenses arranged along an optical axis, a lens barrel that houses and holds this lens group, and an aperture member arranged between at least one of the lenses in the lens group (see, for example, Patent Document 1).

[0003] A lens unit (camera module) having the above configuration can be used in various optical devices, not limited to vehicle-mounted cameras, but particularly when exposed to the external environment in cold regions, as freezing of the lens or accumulation of snow on the lens can be expected, it is generally provided with a snow melting function, etc. Specifically, for example, as shown in Fig. 5, in order to warm up first lens 101, which is positioned closest to the object among lens group L housed and held in lens barrel 120 and exposed from lens barrel 120 (exposed to the external environment), heater 130, for example a PTC (positive temperature coefficient) heater, is interposed between surface 101a facing the image side of first lens 101 and surface 102a facing the object side of second lens 102 adjacent to first lens 101. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-231993 Summary of the Invention [Problem to be solved by the invention]

[0005] In a lens unit equipped with such a heater 130, the heat generated by the heater 130 may adversely affect the anti-reflection coating on the lens surface. Specifically, a typical anti-reflection coating is formed by alternately laminating a first film formed from a vapor deposition material having a first refractive index and a second film formed from a vapor deposition material having a second refractive index higher than the first refractive index. In many cases, a ceramic material (such as SiO2 or Al2O3) or a titanium-based material (such as TiO2) is used. For example, the first film is made of a material mainly containing SiO2, and the second film is made of a material mainly containing Al2O3 or TiO2. However, when such a reflective coating is provided on the surface of the first lens 101, which is directly exposed to the heat of the heater, the anti-reflection coating is repeatedly exposed to the heat from the heater, which causes deterioration of the film structure and makes the coating more susceptible to damage.

[0006] It is known that ceramic materials in particular can deteriorate due to thermal shock fatigue, resulting in cracks and other damage, when subjected to repeated thermal shocks over an extended period of time, even if the temperature difference is relatively small. For this reason, even though heater 130 generally only raises the temperature of first lens 101 to around 120°C, ceramic materials for the anti-reflection coating that are repeatedly exposed to such temperatures over an extended period of time will inevitably develop cracks on their surfaces, even for materials such as Al2O3 that are resistant to thermal shocks above this temperature, apart from SiO2, which has high thermal shock resistance. Such cracks can adversely affect the optical properties of the lens unit, and must therefore be reliably prevented.

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a lens unit and a camera module that prevent the anti-reflection film on the lens surface from being adversely affected by the heat of a heater that warms the lens. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention provides a coated lens provided at an end of a lens barrel on the object side, the coated lens having an anti-reflection coating formed on a surface thereof, the antireflection film is formed by alternately laminating first films made of a first material having a first refractive index and second films made of a second material having a second refractive index higher than the first refractive index, The first material and the second material are characterized by having a thermal shock resistance of 500° C. or higher.

[0009] The inventors have discovered that the thermal shock resistance of the material that forms the anti-reflection coating plays a major role in the adverse effect that snow-melting heaters that repeatedly heat lenses over long periods of time have on the anti-reflection coating on the lens.As a result of repeated experiments, they have found that, particularly in the case of snow-melting heaters that heat lenses up to, for example, about 120°C, when the anti-reflection coating is formed by alternately laminating a first film formed from a first material having a first refractive index and a second film formed from a second material having a second refractive index higher than the first refractive index, if the thermal shock resistance of the first and second materials is 500°C or higher, the anti-reflection coating can be prevented from deteriorating over time due to the heat of the heater and leading to damage, and the film strength can be maintained at a desired level.

[0010] That is, according to the above-described configuration of the present invention, since the first and second materials forming the anti-reflection coating have a thermal shock resistance of 500°C or higher, even if the coated lens with this anti-reflection coating is used together with a heater (particularly a snow-melting heater that heats the lens up to about 120°C) and is repeatedly exposed to heat from the heater over a long period of time, the anti-reflection coating can be prevented from being adversely affected. This can be particularly beneficial when using ceramic materials as the first and second materials, which can deteriorate due to thermal shock fatigue and cause damage such as cracks when repeatedly exposed to thermal shocks over a long period of time, even with a relatively small temperature difference.

[0011] In the above configuration, the thermal shock resistance of the material is evaluated and measured in accordance with the "Thermal Shock Test Method for Fine Ceramics" specified in JIS R1648:2002. In the above configuration, the anti-reflection coating is provided on at least the surface of the coated lens facing the object side, but it may also be provided on the surface of the coated lens facing the image side. Furthermore, in the above configuration, the coated lens may be made of glass or resin.

[0012] Furthermore, in the above-described configuration of the present invention, when ceramic materials are used as the first and second materials, it is preferable that the first material be primarily composed of SiO2 and the second material be primarily composed of Si3N4. By using Si3N4, which has particularly good thermal conductivity, heat from the heater can be transmitted efficiently, and when using a heater to melt snow on the surface of a film-coated lens, for example, the snow melting time can be shortened.

[0013] In addition, in the above-mentioned configuration of the present invention, it is preferable to provide a hydrophilic film on the anti-reflection film. In this way, providing a hydrophilic film on the anti-reflection film instead of a water-repellent film can shorten the snow melting time and improve the visibility of the film-coated lens, especially when the film-coated lens is used together with a snow-melting heater and the heater is used to melt snow on the surface of the film-coated lens. Due to the hydrophilic effect of the hydrophilic film, providing a water-repellent film on the anti-reflection film promotes the spherical formation of water droplets under the water-repellent effect, so that small water droplets are heated by the heater, limiting the heat transfer area and reducing heating efficiency, resulting in a longer snow melting time. However, providing a hydrophilic film on the anti-reflection film allows the fine water droplets adhering to the lens surface to spread over the hydrophilic film, which has a high surface free energy, to form a thin water film. Therefore, a larger water film is heated by the heater, expanding the heat transfer area and improving heating efficiency, thereby shortening the snow melting time. Furthermore, the hydrophilic film can also improve visibility by spreading water droplets that reduce visibility into a film.

[0014] In addition, the hydrophilic film can be formed by vapor deposition, coating, spraying, dipping, etc., with or without masking by taping, but from the viewpoint of increasing the adhesion strength of the film, it is preferable to form the hydrophilic film by vapor deposition.In particular, if the hydrophilic film is formed on the anti-reflection film by vapor deposition, it can contribute to improving the adhesion of the hydrophilic film to the lens surface, especially when the lens is a glass lens.That is, when the hydrophilic film is formed directly on the lens surface, it is necessary to match the composition of the entire hydrophilic film with that of the lens, in order to improve the adhesion between the lens surface and the hydrophilic film, which is troublesome and costly.However, when the hydrophilic film is formed on the lens surface via the anti-reflection film as in the above-mentioned configuration of the present invention, SiO2, which is a general component of the anti-reflection film, is present at the interface between the anti-reflection film and the hydrophilic film, so that the compatibility of the adhesion between the hydrophilic film and the anti-reflection film is good, and therefore it is only necessary to carry out composition modification, etc., to improve adhesion only at the interface between the anti-reflection film and the glass surface. This means that the same adhesion strength can be stably achieved by always using the same hydrophilic film specifications without requiring significant effort or cost.

[0015] In the above configuration, a hydrophilic film is a thin film with hydrophilic properties, with a contact angle of a water droplet of 40 degrees or less. In contrast, a water-repellent film is a thin film with water-repellent properties, with a contact angle of a water droplet of 90 degrees or more, which distinguishes it from a hydrophilic film. In this case, the contact angle is measured using the sessile drop method (A·half-angle·Method), in which a 2.5-microliter water droplet is placed on the lens surface on which the film is formed, so as to minimize the influence of the lens surface. The curved surface connecting the left and right endpoints of the droplet is considered to be a straight line, and the contact angle of the water droplet is measured.

[0016] The present invention also provides a lens unit including a lens group in which a plurality of lenses are arranged along the optical axes of the lenses, and a lens barrel in which the lens group is housed, The lens barrel is provided with a film-coated lens of the above-described configuration at the object-side opening, and a heater is interposed between the surface of the film-coated lens facing the image side and the surface of the lens adjacent to the film-coated lens facing the object side.

[0017] In this way, when the film-coated lens having the above-described configuration is used together with a heater, it can exhibit its inherent characteristics and provide the excellent effects described above. In the above-described configuration of the present invention, the "heater" may be, for example, a PTC (positive temperature coefficient) heater. Furthermore, in the above-described configuration, if the film-coated lens adjacent to and in contact with the heater is a glass lens, the surface facing the image side may be blackened to block light and prevent ghosting.

[0018] The present invention also provides a camera module including the lens unit, which can achieve the same effects as the above-described film-coated lens and lens unit. [Effects of the Invention]

[0019] According to the present invention, since the thermal shock resistance of the first and second materials forming the anti-reflection coating is 500°C or higher, even if a coated lens with this anti-reflection coating is used together with a heater and is repeatedly exposed to heat from the heater over a long period of time, the anti-reflection coating can be prevented from being adversely affected. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic cross-sectional view of a lens unit according to an embodiment of the present invention, which includes a heater. [Figure 2] 2 is a schematic diagram showing a laminated structure of an anti-reflection film of a film-coated lens of the lens unit of FIG. 1. FIG. [Figure 3]FIG. 1(a) is a schematic diagram showing how heater heat is transmitted when a water-repellent film is provided on an anti-reflection film, and FIG. 1(b) is a schematic diagram showing how heater heat is transmitted when a hydrophilic film is provided on an anti-reflection film. [Figure 4] 2 is a schematic cross-sectional view of a camera module including the lens unit of FIG. 1. [Figure 5] FIG. 1 is a schematic cross-sectional view of a conventional lens unit equipped with a heater. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The lens unit of the present embodiment described below is particularly for use in a camera module such as an in-vehicle camera, and is fixedly installed on the exterior surface of the vehicle, with wiring drawn into the vehicle and connected to a display or other device. Furthermore, hatching is omitted for the multiple lenses in Figures 1 to 5, except for the first lens.

[0022] FIG. 1 shows a lens unit 11 according to an embodiment of the present invention, which includes a heater. As shown, the lens unit 11 of this embodiment includes a cylindrical lens barrel 12, e.g., made of metal; multiple lenses arranged within a stepped inner storage space S of the lens barrel 12, e.g., four lenses consisting of, from the object side, a first lens 13, a second lens 14, a third lens 15, and a fourth lens 16; and an aperture member 22. In this embodiment, the aperture member 22 is interposed between the third lens 15 and the fourth lens 16 and serves as an "aperture diaphragm" that limits the amount of transmitted light and determines the F-number, which is an index of brightness, or a "light-blocking diaphragm" that blocks light rays that cause ghosting or aberrations. An in-vehicle camera equipped with such a lens unit 11 includes the lens unit 11, a circuit board (not shown) having an image sensor, and an installation member (not shown) for installing the circuit board in a vehicle such as an automobile.

[0023] The multiple lenses 13, 14, 15, and 16 incorporated and housed within the internal housing space S of the lens barrel 12 are stacked and arranged with their optical axes aligned. The lenses 13, 14, 15, and 16 are aligned along a single optical axis O to form a lens group L used for imaging. In particular, in this embodiment, the first lens 13 is a spherical glass lens, and the second lens 14, third lens 15, and fourth lens 16 are each made of resin. However, this is not limiting. For example, the second to fourth lenses may be glass lenses, and the first lens and lens barrel 12 may be made of resin. The first lens 13, located at the object-side end (opening) of the lens barrel 12, is a coated lens with an anti-reflection coating and a hydrophilic coating, as described below. Therefore, hereinafter, the first lens 13 may also be referred to as a coated lens. The second lens 14, the third lens 15, and the fourth lens 16 are also provided with anti-reflection coatings.

[0024] A cap 23 is screwed onto the object side end of the lens barrel 12 (the upper end in FIG. 1), and this cap 23 secures the first lens 13, which is positioned closest to the object side of the lens group L, to the object side end of the lens barrel 12. Of course, if the lens barrel 12 is made of resin, the object side end of the lens barrel 12 may be crimped radially inward to secure the first lens 13 to the object side end of the lens barrel 12.

[0025] Furthermore, an inner flange portion 24 having an opening with a diameter smaller than that of fourth lens 16 is provided at the end (the lower end in FIG. 1) of lens barrel 12 on the image side. This inner flange portion 24 and cap 23 hold and fix in place in lens barrel 12 the plurality of lenses 13, 14, 15, and 16 that make up lens group L and diaphragm member 22 in the optical axis direction.

[0026] An O-ring 26 serving as a seal is provided between the lens barrel 12 and the outer circumferential annular portion of the surface 13b facing the image side of the first lens 13, which is positioned closest to the object, and the gap between them is sealed at the object-side end of the lens barrel 12. This prevents water, dust, and other fine particles from entering the lens barrel 12 from the object-side end of the lens unit 11. An outer flange 25 is provided on the outer circumferential surface of the lens barrel 12 in the shape of a brim and is used when installing the lens barrel 12 in an in-vehicle camera.

[0027] In this embodiment, in order to heat the first lens 13 exposed from the lens barrel 12 (exposed to the external environment) as needed (for purposes such as melting snow), an annular heater 40 is interposed between a surface 13b facing the image side of the first lens 13 and a surface 14a facing the object side of the second lens 14 adjacent to the first lens 13. In particular, in this embodiment, the heater 40 is formed as a PTC (positive temperature coefficient) heater, and heats the first lens 13 to, for example, about 120°C. The heater 40 is supplied with power from a power source (not shown) via a conductor 73.

[0028] In this embodiment, antireflection coatings 30 are provided on the concave portions of surface 13a facing the object side and surface 13b facing the image side of glass first lens 13. These antireflection coatings 30 are provided over at least the range of the effective diameter of first lens 13. A hydrophilic film 32 is further provided on antireflection coating 30 provided on lens surface 13a facing the object side. Although not clearly shown, a black coating is applied to the portion of surface 13b facing the image side of first lens 13 that is in contact with heater 40 to block light and prevent ghosting.

[0029] As clearly shown in Figure 2, the antireflection coating 30 provided on the surfaces 13a and 13b of the first lens 13 (which is a coated lens) (Figure 2 depicts the antireflection coating 30 provided on the surface 13a together with the hydrophilic coating 32) is formed by alternately laminating first films 30b formed from a first material having a first refractive index, such as SiO2, or a first material mainly composed of SiO2, and second films 30a formed from a second material having a second refractive index higher than the first refractive index, such as Si3N4, or a second material mainly composed of Si3N4, and is formed on the surfaces 13a and 13b of the first lens 13 by, for example, vapor deposition. Here, for example, the first material is a low-refractive-index material with a refractive index of 1.46, and the second material is a high-refractive-index material with a refractive index of 2.02. In this case, the first material, SiO2, has a thermal shock resistance of over 1000°C, and the second material, Si3N4, has a thermal shock resistance of 600 to 650°C. The thicknesses of the SiO2 layer (first film 30b) and Si3N4 layer (second film 30a) are 5 to 150 nm and 5 to 100 nm, respectively. In particular, the anti-reflection coating 30 of this embodiment is formed by stacking six layers in total, with a total thickness of 240 nm. 2, the second film 30a is laminated next to the surface 13a of the lens 13, and then the first film 30b is laminated in this order, but the second film 30a and the first film 30b may be interchanged. Specifically, the order may be lens surface 13a / first film 30b / second film 30a / first film 30b / second film 30a / ... with an optimal thickness.

[0030] 4 is a schematic cross-sectional view of a camera module 300 of this embodiment having a lens unit 11 configured as described above with filter 100 attached. As shown in the figure, camera module 300 includes an upper case (camera case) 301, which is an exterior component, and a mount (base) 302 that holds lens unit 11. Camera module 300 also includes a sealing member 303 and a package sensor (imaging element) 304.

[0031] Upper case 301 is a member that exposes the object-side end of lens unit 11 and covers the other portions. Mount 302 is disposed inside upper case 301, and has female threads 302a that mesh with male threads 11a of lens unit 11. Sealing member 303 is a member that is interposed between the inner surface of upper case 301 and outer peripheral surface 12a of barrel 12 of lens unit 11 while placed on outer flange portion 25, and is a member that maintains airtightness inside upper case 301.

[0032] Package sensor 304 is disposed inside mount 302 and is positioned to receive the image of the object formed by lens unit 11. Package sensor 304 also includes a CCD, CMOS, or the like, and converts the light that is collected and reaches it through lens unit 11 into an electrical signal. The converted electrical signal is then converted into analog data or digital data, which are components of the image data captured by the camera.

[0033] As described above, according to this embodiment, the first and second materials (SiO2, Si3N4) that form the anti-reflection coating 30 have a thermal shock resistance of 500°C or higher, so even if the coated lens 13 including this anti-reflection coating 30 is repeatedly exposed to heat from the heater 40 over a long period of time, the anti-reflection coating 30 can be prevented from being adversely affected. This can be particularly beneficial when, as in this embodiment, the first and second materials are ceramic materials that, when repeatedly exposed to thermal shocks over a long period of time even at a relatively low temperature difference, can deteriorate due to thermal shock fatigue and cause damage such as cracks.

[0034] Furthermore, in this embodiment, Si3N4, which has good thermal conductivity, is used as the second material of the anti-reflection coating 30, so that the heat from the heater 40 can be transmitted efficiently, and when the heater 40 is used to melt snow on the surface of the coated lens 13, the snow melting time can be shortened.

[0035] Furthermore, in this embodiment, a hydrophilic film 32 is provided on the anti-reflection film 30 instead of a water-repellent film, and therefore, due to the hydrophilic properties of the hydrophilic film 32, the snow melting time can be shortened compared to a water-repellent film, and the visibility of the film-coated lens 13 can also be improved. 3(a), if a water-repellent film 150 is provided on the anti-reflection film 30, the water-repellent effect encourages the spherical formation of water droplets 80, so that small water droplets 80 are heated by the heater 40 (the direction of heat transfer is indicated by arrows in FIG. 3), limiting the heat transfer area, reducing heating efficiency, and lengthening the snow melting time. However, if a hydrophilic film 32 is provided on the anti-reflection film 30 as shown in FIG. 3(b), the hydrophilic effect causes fine water droplets that adhere to the surface of the lens 13 to spread over the hydrophilic film, which has high surface free energy, to form a thin water film 82. This allows the heater 40 to heat the large water film 82, expanding the heat transfer area, improving heating efficiency, and shortening the snow melting time. Furthermore, the hydrophilic film 32 also improves visibility by spreading the water droplets 80, which would otherwise reduce visibility, into a thin film.

[0036] Although the present invention has been described above in relation to specific embodiments, the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the present invention. For example, in the present invention, the shapes of the lenses, lens barrels, anti-reflection coatings, and heaters are not limited to the above-described embodiments. Furthermore, some or all of the above-described embodiments may be combined, or part of the configuration may be omitted from one of the above-described embodiments, without departing from the spirit of the present invention. [Explanation of symbols]

[0037] 11 Lens unit 12 Telescope tube 13 First Lens 14 Second Lens 30 Anti-reflection coating 32 Hydrophilic membrane 40 Heater 300 Camera Module L lens group O optical axis

Claims

1. A lens unit comprising a lens group in which multiple lenses are arranged along the optical axis of the lens, and a lens barrel in which this lens group is housed, The lens group housed in the lens barrel includes a first lens closest to the object and a second lens adjacent to the first lens on the image side. The surface of the first lens facing the image side consists of a radially inward concave surface and a radially outward flat annular surface. The surface of the second lens facing the object has a radially outward flat annular surface that is opposite to the annular surface of the first lens. A heater is interposed between the annular surface of the first lens and the annular surface of the second lens. An anti-reflective coating is formed on the concave surface of the first lens and on the surface of the first lens facing the object, by alternately laminating a first film formed from a first material having a first refractive index and a second film formed from a second material having a second refractive index higher than the first refractive index. A lens unit characterized in that a hydrophilic film is formed on the anti-reflective film on the surface of the first lens facing the object.

2. The opposing surface of the lens barrel that faces the annular surface of the first lens has an annular surface that is radially inward and an annular recess that is radially outward, The heater extends between the annular surface of the first lens, the annular surface of the second lens, and the annular surface of the lens barrel. A sealing member is interposed between the annular surface of the first lens and the opposing surface of the lens barrel, positioned within the annular recess of the lens barrel. The heater's conductor is led out to the outside of the lens barrel through the annular recess of the lens barrel. The lens unit according to feature 1.

3. The lens unit according to claim 1, characterized in that the first material mainly consists of SiO2 and the second material mainly consists of Si3N4.

4. A camera module comprising the lens unit described in claims 1 to 3, wherein an image sensor is positioned to receive the image formed by the lens unit.

Images