Optical unit and distance image capturing device

Abstract

This optical unit comprises: an element substrate on which an image sensor is disposed; a sensor cover attached to the element substrate so as to cover the image sensor; and a lens holder to which a lens is attached. The lens holder and the sensor cover are joined to each other. The optical unit comprises, in the portion where the lens holder and the sensor cover are joined, a first stray light suppression unit that suppresses the occurrence of stray light entering the optical unit.

Description

Optical Unit and Distance Image Capturing Device

[0001] The present invention relates to an optical unit. A distance image capturing device using this optical unit will also be referred to. This application claims priority from Japanese Patent Application No. 2024-231530 filed in Japan on December 27, 2024, the content of which is incorporated herein by reference.

[0002] In ensuring and improving the performance of an imaging device, it is important to accurately align (align) an image sensor and a lens system that guides light to this image sensor. Separately from that, it is also important to minimize light such as stray light or disturbance light that enters the interior from outside the lens system.

[0003] In this regard, Patent Document 1 discloses a technique of disposing a light-shielding member provided with an annular or notch-annular light-shielding protrusion between a stage that holds a lens unit and a substrate on which an image sensor is mounted.

[0004] Japanese Patent No. 6133988 Gazette

[0005] In Patent Document 1, as an application target of the technique, a stereo camera having a pair of imaging modules is cited. Each imaging module is assumed to have visible light as the light that enters the interior in order to acquire a visible light image.

[0006] On the other hand, in a distance image capturing device, in some aspects such as that infrared light or the like that is not visible light is often used and that light for distance measurement is irradiated from a light source provided by itself, it is different from a general imaging device such as the above-described stereo camera. Therefore, although details will be described later, it is not easy to achieve both high-precision alignment and suppression of stray light or the like by simply applying the technique of Patent Document 1.

[0007] In view of the above circumstances, an object of the present invention is to provide an optical unit that easily achieves both high-precision alignment and suppression of stray light or the like.

[0008] An optical unit according to a first aspect of the present invention comprises an element substrate on which an image sensor is arranged, a sensor cover attached to the element substrate so as to cover the image sensor, and a lens holder on which a lens is attached, with the lens holder and the sensor cover being joined together. This optical unit is provided with a stray light suppression unit at the joint between the lens holder and the sensor cover to suppress the generation of stray light entering the optical unit.

[0009] A distance image capturing device according to a second embodiment of the present invention comprises an optical unit according to the first embodiment.

[0010] According to the present invention, it is possible to provide an optical unit that can easily achieve both high-precision alignment and suppression of stray light.

[0011] This is a perspective view showing a camera according to the first embodiment of the present invention. This is a schematic diagram showing the general configuration of the camera in Figure 1. This is a diagram showing the camera in Figure 1 in an exploded view. This is a diagram showing the imaging unit of the camera in Figure 1 in an exploded view. This is a cross-sectional view of the optical unit related to the imaging unit in Figure 4. This is a schematic cross-sectional view showing the joint between the lens holder and the sensor cover in the optical unit in Figure 5. This is a schematic cross-sectional view showing the joint between the lens holder and the sensor cover in a modified example of the optical unit in Figure 5. This is a schematic diagram showing the lens holder and sensor cover in a modified example. This is a schematic diagram showing the lens holder and sensor cover in a modified example. This is a schematic cross-sectional view showing the joint between the sensor cover and the element substrate in the optical unit according to the second embodiment of the present invention. This is a schematic diagram showing the element substrate in a modified example of the optical unit in Figure 11. This is a schematic cross-sectional view showing the joint between the sensor cover and the element substrate in a modified example of the optical unit in Figure 11. This is a schematic cross-sectional view showing the optical unit according to a modified example of the present invention.

[0012] A first embodiment of the present invention will be described with reference to Figures 1 to 10. Figure 1 is a perspective view showing a camera 1, which is a distance image capturing device according to this embodiment. The camera 1 has a rectangular parallelepiped shape defined by a metal housing 10. The housing 10 has a first aperture 2 for imaging and a second aperture 3 for a light source that emits reference light on its front. Two second apertures 3 are provided so as to sandwich the first aperture 2.

[0013] Figure 2 shows a schematic diagram of the camera 1's configuration. Inside the housing 10 are a power supply board 20, a main board 30, and an imaging unit 40. The power supply board 20 is connected to a power supply and generates voltages to drive each part of the camera 1. The main board 30 is composed of integrated circuits and is connected to the power supply board 20 and the imaging unit 40. The main board controls the operation of the power supply board 20 and the imaging unit 40, and performs correction processing of the data handled by the imaging unit 40. A hub 31 used for connecting to the power supply Es and an external computer 200 is also connected to the main board. There are no particular restrictions on the integrated circuits included in the main board 30, and FPGAs (Field-Programmable Gate Arrays), ASICs (Application Specific Integrated Circuits), CPUs, etc., can be appropriately selected and used.

[0014] Figure 3 is a diagram showing the camera 1 in an exploded view. The imaging unit 40 comprises a light source substrate 41 to which a light source is attached, and an optical unit 50 including a lens and an image sensor. The optical unit 50 is an optical unit according to the present invention. The housing 10 has a main body 11 with an internal space and a lid 12. The power supply board 20, the main board 30, and the imaging unit 40 are arranged inside the main body 11, and the lid 12 is screwed to the main body 11, sealing them inside the housing 10. A rubber gasket 13 is placed between the main body 11 and the lid 12, ensuring waterproofing inside the housing 10 when the lid 12 is attached. Light-shielding covers 4 are attached to the first opening 2 and the second opening 3, and are configured to prevent most natural light, etc., that is not used for acquiring distance images (described later), from entering the housing 10.

[0015] Figure 4 shows an exploded view of the imaging unit 40. The imaging unit 40 in this embodiment uses two vertical cavity surface-emitting lasers (VCSELs) as light sources, with two VCSELs 42 mounted on a light source substrate 41. The VCSELs 42 are just an example, and other light sources can of course be used. The optical unit 50 includes a lens barrel 51 to which a lens 52 is attached, a lens holder 53 to which the lens barrel 51 is fixed, and an element substrate 55 on which an image sensor 56 is mounted. For example, a CMOS image sensor can be used as the image sensor 56, and it is mounted on the surface of the element substrate 55 facing the first aperture 2. Furthermore, the image sensor 56 is covered by a sensor cover 61 to which a bandpass filter 62 is attached. The image sensor 56 is configured such that light incident on the image sensor 56 after passing through the lens 52 passes through the bandpass filter 62 before reaching the image sensor 56.

[0016] A metal support block 60 is positioned around the lens 52 and lens holder 53 between the light source substrate 41 and the element substrate 55. The support block 60 is in contact with the light source substrate 41 and the element substrate 55. The support block 60 is configured so that the heat generated when the VCSEL 42 and image sensor 56 are driven is released to the outside of the housing 10 via the support block 60.

[0017] In the sensor cover 61, on the surface opposite to the surface facing the image sensor 56, an alignment protrusion (first protrusion) 63 is formed around the bandpass filter 62. In this embodiment, the protrusion 63 is a square frame shape when viewed from the front and is positioned approximately concentrically with the bandpass filter 62.

[0018] Figure 5 is a cross-sectional view of the optical unit 50. In the lens holder 53, an alignment groove 53a, which has a roughly square shape when viewed from the front, is formed on the lower side facing the sensor cover 61. In the direction perpendicular to the optical axis of the lens 52 (left-right direction in Figure 6), the width of the alignment groove 53a is wider than the width of the protrusion 63 of the sensor cover 61. As a result, the dimensional relationship between the alignment groove 53a and the protrusion 63 is configured such that the entire protrusion 63 can enter the alignment groove 53a, and in that state, the lens holder 53 and the sensor cover 61 can move relative to each other within a certain range.

[0019] During the manufacturing of the optical unit 50, the lens holder 53 and the element substrate 55 are fabricated separately, and the lens holder 53 and the sensor cover 61 are joined together with the lens 52 and the image sensor 56 aligned. In this alignment, both adjustments are made: an adjustment in the planar direction along the light-receiving surface of the image sensor 56 to adjust the optical axis position of the lens 52 relative to the image sensor 56, and an adjustment in the direction perpendicular to the planar direction (up and down direction in Figure 4: optical axis direction) to adjust the distance between the lens 52 and the image sensor 56.

[0020] Alignment is performed by inserting the protrusion 63 of the sensor cover 61 into the alignment groove 53a of the lens holder 53, lightly fixing the two together with adhesive, and checking the image acquired by the image sensor 56. Once the alignment is complete, the adhesive is allowed to fully cure, fixing the positional relationship between the lens holder 53 and the sensor cover 61, and completing the optical unit 50. Light-curing adhesives such as UV-curing adhesives are suitable for the alignment work described above. Since there are individual differences on both the lens holder 53 and the element substrate 55, the relative positional relationship between the lens holder 53 and the sensor cover 61 in the completed optical unit 50 will basically differ from one unit to another.

[0021] Camera 1 acquires a distance image based on the reflected light from the VCSEL 42, which is the light source, reflected by the target object, using an image sensor 56, and measures the distance to the object using the time-of-flight (TOF) method. In Camera 1, due to the presence of the light-shielding cover 4 described above, almost no visible light with a wavelength significantly different from the reference light enters the housing 10, but it is not possible to completely prevent natural light with the same or similar wavelength as the reference light from entering the housing 10. Furthermore, a small portion of the reference light emitted from VCSEL 42 is reflected by the light-shielding cover 4 and remains inside the housing 10. When this light enters the inside of the optical unit 50 and reaches the image sensor 56, it becomes stray light that generates noise and adversely affects the distance measurement performance of Camera 1.

[0022] In the optical unit 50, the gap between the lens holder 53 and the sensor cover 61 is one of the main entry points for stray light. Furthermore, due to the alignment described above, adhesive 71 is placed between the lower surface of the lens holder 53 and the sensor cover 61, so they may be fixed in a state where they do not come into contact with each other, in which case the possibility of stray light entering increases. In the optical unit 50 according to this embodiment, the protrusion 63 of the sensor cover 61 is inserted into the alignment groove 53a of the lens holder 53 and the two are fixed in this state, and the alignment groove 53a and the protrusion 63 form a stray light suppression section (first stray light suppression section) 100. For this reason, as shown in Figure 6, one of the inner surfaces of the alignment groove 53a is always inside the protrusion 63. As a result, much of the light that enters through the gap is reflected by this inner surface, and the amount of light reaching the bandpass filter 62 is significantly reduced. As a result, it is possible to contribute to suppressing both the generation of stray light and the amount of light if it occurs.

[0023] The configuration of the stray light suppression part for reducing stray light generated by the gap between the lens holder 53 and the sensor cover 61 according to this embodiment is not limited to the above-described configuration. In the modified example shown in Figure 7, the lens holder 53 does not have an alignment groove 53a, and only a peripheral wall 54 for defining the range of relative movement protrudes downward. Furthermore, after fixing the lens holder 53 and the sensor cover 61, a light-shielding paste 72 that functions as a stray light suppression part is placed around the entire perimeter of the lens holder 53 so as to cover the adhesive 71 located in the gap between the lens holder 53 and the sensor cover 61. Even with such a configuration, stray light generated by the gap between the lens holder 53 and the sensor cover 61 can be reduced. It goes without saying that this configuration may be combined with an alignment groove 53a.

[0024] In the modified example shown in Figure 8, the cross-sectional shape of the protrusion 63A has a slope, and the inner surface of the alignment groove 53a is also inclined. In this way, if the height of the protrusion and the depth of the alignment groove are the same, the contact area of ​​the adhesive can be increased compared to the embodiment shown, and the lens holder 53 and the sensor cover 61 can be joined more firmly. The slope may be provided on only one of the protrusion and the alignment groove, or the inclination angle of the slope may be different for the protrusion and the alignment groove.

[0025] In the modified example shown in Figure 9, the lower end of the lens holder 53 protrudes in a flange-like shape, further providing the lens holder 53 with a shade 73 (first stray light suppression part) that functions as a stray light suppression part. Such a shade is highly effective in preventing light reflected by the light-shielding cover 4 after being irradiated from the VCSEL 42 from entering the gap between the lens holder 53 and the sensor cover 61. The effect of the shade 73 is enhanced by extending it outward beyond the sensor cover 61, as shown in the figure, but this is not essential, and it may be sized to remain within the range of the sensor cover 61 when viewed from the front. It is also possible to provide a shade that protrudes inward instead of, or in addition to, the shade 73. In the modified example shown in Figure 9, the alignment groove 53a of the lens holder 53 and the protrusion 63 of the sensor cover 61 are shown, but they are not necessarily required.

[0026] In the modified example shown in Figure 10, the sensor cover 61 is further provided with a second protrusion 65 (first stray light suppression part) that functions as a stray light suppression part, within the area surrounded by the protrusion 63. In this way, some of the light that passes through the gap between the lens holder 53 and the sensor cover 61 and enters the lens holder 53 is reflected, further reducing the amount of light that reaches the bandpass filter 62. The position and height of the second protrusion 65 can be appropriately set within a range that does not interfere with the lens holder 53 during the alignment process and does not interfere with the lens holder 53 and lens 52 during bonding, and a higher height will yield a greater effect.

[0027] Note that in Figures 8, 9, and 10, the lens holder 53 and the sensor cover 61 are shown spaced apart for clarity in explaining the configuration. During alignment, the protrusion 63 of the sensor cover 61 is inserted into the alignment groove 53a of the lens holder 53, and after position adjustment, the positional relationship between the lens holder 53 and the sensor cover 61 is fixed, completing the optical unit 50.

[0028] A second embodiment of the present invention will be described with reference to Figures 11 to 12. In the following description, components that are common to those already described will be denoted by the same reference numerals, and redundant descriptions will be omitted. Another entry point for stray light in the optical unit 50 is the joint between the sensor cover 61 and the element substrate 55. The sensor cover 61 does not require very high precision alignment and is usually installed without alignment, so a large gap is unlikely to occur between the sensor cover 61 and the element substrate 55. However, since the light that enters can easily reach the image sensor 56, it is preferable to take countermeasures. In this embodiment, a configuration for suppressing such stray light will be described.

[0029] The sensor cover 61 of this embodiment shown in Figure 11 has a light-shielding wall 81 that protrudes downward inward from the peripheral wall 80 that protrudes downward and is joined to the element substrate 55. As a result, most of the light that enters through the gap between the peripheral wall 80 and the element substrate 55 is reflected by the light-shielding wall (second stray light suppression part) 81, which functions as a stray light suppression part, and is prevented from reaching the image sensor 56. The light-shielding wall 81 is preferably formed to surround the image sensor in the direction normal to the light-receiving surface of the image sensor 56. As long as it surrounds the image sensor, there is no preference for its shape, and any desired shape such as a circular frame or a polygonal frame can be set considering interference with other components on the element substrate 55. The protruding length of the light-shielding wall 81 is preferably set to be as long as possible without causing interference with the element substrate 55 when the sensor cover 61 is installed.

[0030] The configuration of the stray light suppression unit that suppresses stray light entering from between the sensor cover 61 and the element substrate 55 is not limited to that described above. The modified element substrate 55A shown in Figure 12 has a light absorbing unit 82 that functions as a stray light suppression unit around the image sensor 56. As a result, much of the light approaching the image sensor 56 while reflecting off the sensor cover 61 is captured by the light absorbing unit and prevented from reaching the image sensor 56. Examples of the light absorbing unit 82 include black or dark-colored materials, which can be formed by attaching a sheet-like material or by applying and curing a paste. If the surface of the light absorbing unit 82 is excessively smooth, light that is not absorbed and is reflected is more likely to occur, so it is preferable that the surface of the light absorbing unit 82 has a moderate roughness. Depending on the material of the light absorbing unit 82, it is also possible to expect the effect of suppressing the temperature rise of the image sensor during the operation of the camera 1 by absorbing the heat emitted by the image sensor 56. Examples of materials that can be expected to have this effect include graphite and silicone.

[0031] The embodiments shown in Figures 11 and 12 are examples in which the configuration that functions as a stray light suppression unit is located in the space surrounded by the sensor cover 61 and the element substrate 55. As another example, as shown in Figure 13, even if a groove 83 is formed in the element substrate 55 and the sensor cover 61 and the element substrate 55 are joined with the peripheral wall 80 entering into the groove 83, the peripheral wall 80 and the groove 83 function as a stray light suppression unit located at the joint between the sensor cover 61 and the element substrate 55, thereby suppressing stray light entering from between the sensor cover 61 and the element substrate 55.

[0032] The configurations described in this embodiment can be combined in pairs or more. Furthermore, since the provided parts differ from those of the first embodiment, it is possible to further reduce stray light generation by combining them with each aspect of the first embodiment, including modified versions.

[0033] Although each embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments, and modifications and combinations of the configuration are also included without departing from the spirit of the present invention.

[0034] For example, a stray light suppression section may be provided in a part not mentioned in the above-described embodiment. Besides the paths described above, the gap between the lens barrel 51 and the lens 52 may also be a path for stray light to enter. However, in this case, for example, by providing a shade 91 that protrudes outward from the outer circumference of the lens barrel 51A in the modified example shown in Figure 14, the shade 91 reduces the amount of light entering from the gap between the lens barrel 51A and the lens 52 and functions as a stray light suppression section. Such a configuration is particularly effective for light that has been irradiated from the VCSEL 42 and reflected by the light-shielding cover 4. The stray light suppression section corresponding to the gap between the lens barrel 51 and the lens 52 is not limited to the embodiment shown in Figure 14. Furthermore, such a stray light suppression section can be combined with either one or both of the first and second embodiments.

[0035] According to the present invention, it is possible to provide an optical unit that can easily achieve both high-precision alignment and suppression of stray light.

[0036] 1 Camera (distance image acquisition device) 2 First aperture 3 Second aperture 4 Light-shielding cover 10 Housing 11 Main body 12 Lid 13 Rubber gasket 20 Power supply board 30 Main board 40 Imaging unit 41 Light source board 42 VCSEL 50 Optical unit 51 Lens barrel 52 Lens 53 Lens holder 53a Alignment groove 55 Element board 56 Image sensor 61 Sensor cover 63, 63A Protrusion 65 Second protrusion 71 Adhesive 72 Light-shielding paste 73 Shade 81 Light-shielding wall (second stray light suppression unit) 82 Light absorption unit 100 First stray light suppression unit

Claims

1. An optical unit comprising an element substrate on which an image sensor is arranged, a sensor cover attached to the element substrate so as to cover the image sensor, and a lens holder on which a lens is attached, wherein the lens holder and the sensor cover are joined together, and a first stray light suppression unit is provided at the joint between the lens holder and the sensor cover to suppress the generation of stray light entering the optical unit.

2. The optical unit according to claim 1, wherein the lens holder and the sensor cover are joined by an adhesive, the first stray light suppression portion comprises an alignment groove provided in the lens holder and a first protrusion provided in the sensor cover that enters into the alignment groove, and in a direction perpendicular to the optical axis of the lens, the width of the alignment groove is wider than the width of the first protrusion of the sensor cover.

3. The optical unit according to claim 2, wherein the first stray light suppression unit has a second protrusion provided on the sensor cover within the area surrounded by the first protrusion.

4. The optical unit according to claim 2, wherein the first stray light suppression unit has a shade that extends in a flange shape from the lower end of the lens holder.

5. The optical unit according to claim 2, wherein the first stray light suppression portion has a light-shielding paste provided around the entire periphery of the lens holder so as to cover the adhesive.

6. The optical unit according to claim 1, further comprising a second stray light suppression unit in the space surrounded by the sensor cover and the element substrate.

7. A distance image capturing device comprising the optical unit described in any one of claims 1 to 6.

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