Optical unit and distance image acquisition device

Abstract

This optical unit provides a balance between high-precision alignment and suppression of stray light. [Solution] An optical unit 50 has an element substrate 55 on which an image sensor 56 is arranged, a sensor cover 61 attached to the element substrate so as to cover the image sensor, and a lens holder 53 to which a lens 52 is attached, and the lens holder and the sensor cover are joined together, and a stray light suppression part is provided at the joint between the lens holder and the sensor cover to suppress the generation of stray light entering into the optical unit.

Description

Technical Field

[0001] The present invention relates to an optical unit. A distance image capturing device using this optical unit is also mentioned.

Background Art

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

[0003] Regarding this point, Patent Document 1 discloses a technique of arranging 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 imaging element is mounted.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0006] On the other hand, in a distance image capturing device, in some points such as often using infrared light or the like that is not visible light, and irradiating light for distance measurement from a light source provided by itself, it is different from a general imaging device such as the above stereo camera. Therefore, as will be explained in detail later, simply applying the technology described in Patent Document 1 does not easily achieve both high-precision alignment and suppression of stray light.

[0007] Based on the above circumstances, the present invention aims to provide an optical unit that can easily achieve both high-precision alignment and suppression of stray light. [Means for solving the problem]

[0008] A first aspect of the present invention is 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. This optical unit includes a stray light suppression section at the joint between the lens holder and the sensor cover to suppress the generation of stray light entering the optical unit.

[0009] A second aspect of the present invention is a distance image imaging device comprising an optical unit according to the first aspect. [Effects of the Invention]

[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. [Brief explanation of the drawing]

[0011] [Figure 1] This is a perspective view showing a camera according to the first embodiment of the present invention. [Figure 2] This is a schematic diagram showing the general configuration of the camera. [Figure 3] This is a diagram showing the camera disassembled. [Figure 4] This diagram shows the imaging unit of the camera disassembled. [Figure 5] This is a cross-sectional view of the optical unit related to the imaging section. [Figure 6] This is a schematic cross-sectional view showing the joint between the lens holder and the sensor cover in the optical unit. [Figure 7] It is a schematic cross-sectional view showing a joint portion between a lens holder and a sensor cover in a modified example of an optical unit. [Figure 8] It is a schematic view showing a lens holder and a sensor cover according to a modified example. [Figure 9] It is a schematic view showing a lens holder and a sensor cover according to a modified example. [Figure 10] It is a schematic view showing a lens holder and a sensor cover according to a modified example. [Figure 11] It is a schematic cross-sectional view showing a joint portion between a sensor cover and an element substrate in an optical unit according to a second embodiment of the present invention. [Figure 12] It is a schematic view showing an element substrate according to a modified example of the optical unit. [Figure 13] It is a schematic cross-sectional view showing a joint portion between a sensor cover and an element substrate according to a modified example of the optical unit. [Figure 14] It is a schematic cross-sectional view showing an optical unit according to a modified example of the present invention.

Embodiments for Carrying Out the Invention

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

[0013] FIG. 2 schematically shows the schematic configuration of the camera 1. Inside the housing 10, a power supply board 20, a main board 30, and an imaging unit 40 are arranged. The power supply board 20 is connected to a power supply and generates a voltage for driving each part of the camera 1. The main board 30 is configured to include an integrated circuit and is connected to the power supply board 20 and the imaging unit 40. The main board performs operation control of the power supply board 20 and the imaging unit 40, correction processing of data handled by the imaging unit 40, and the like. A hub 31 used for connection to the power supply Es and the external computer 200 is also connected to the main board. There is no particular limitation on the integrated circuit included in the main board 30, and an FPGA (Field-Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), a CPU, or the like can be appropriately selected and used.

[0014] FIG. 3 is a diagram showing the camera 1 disassembled. The imaging unit 40 includes a light source board 41 to which a light source is attached, and an optical unit 50 including a lens and an imaging device. The optical unit 50 is an optical unit according to the present invention. The housing 10 has a main body 11 having 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, thereby being sealed inside the housing 10. A rubber packing 13 is arranged between the main body 11 and the lid 12, and the waterproof property inside the housing 10 is ensured in a state where the lid 12 is attached. A light-shielding cover 4 is attached to the first opening 2 and the second opening 3, and is configured such that natural light and the like that are not used for acquiring a distance image (described later) hardly enter the housing 10.

[0015] FIG. 4 shows the imaging unit 40 disassembled. The imaging unit 40 of the present embodiment uses two vertical cavity surface emitting lasers (VCSELs: Vertical Cavity Surface Emitting Laser) as light sources, and two VCSELs 42 are attached to the light source board 41. The VCSEL 42 is an example, and of course, other light sources can also be used. The optical unit 50 comprises 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 the image sensor 56, for example, a CMOS image sensor can be used and 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, and the light incident on the image sensor 56 after passing through the lens 52 is configured to reach the image sensor 56 after passing through the bandpass filter 62.

[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, and 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 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. The width of the alignment groove 53a is wider than the width of the protrusion 63 of the sensor cover 61, so that the entire protrusion 63 can enter the alignment groove 53a, and the lens holder 53 and the sensor cover 61 can move relative to each other within a certain range when the protrusion 63 is entered.

[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) 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 harden, fixing the positional relationship between the lens holder 53 and the sensor cover 61, and completing the optical unit 50. For the alignment work described above, light-curing adhesives such as UV-curing adhesives are suitable. Since there are individual differences on both the lens holder 53 side and the element substrate 55 side, 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 reference light emitted from the light source, VCSEL 42, which is 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, the presence of the aforementioned light-shielding cover 4 virtually prevents visible light with a wavelength significantly different from the reference light from entering the housing 10. However, 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 the VCSEL 42 is reflected by the light-shielding cover 4 and remains inside the housing 10. When this light enters 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 may be placed between the lower surface of the lens holder 53 and the sensor cover 61, resulting in them being fixed in a state where they do not come into contact. In this 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 together, and the alignment groove 53a and the protrusion 63 form a stray light suppression section 100. Therefore, as shown in Figure 6, one of the inner surfaces of the alignment groove 53a is always located 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. Consequently, it is possible to suppress both the generation of stray light and the amount of light if stray light is generated.

[0023] The configuration of the stray light suppression unit for reducing stray light generated by the gap between the lens holder 53 and the sensor cover 61 in 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, which 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 this configuration, stray light generated by the gap between the lens holder 53 and the sensor cover 61 can be reduced. Naturally, this configuration may also 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 or the alignment groove, or the inclination angle of the slope may differ between 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, giving the lens holder 53 a shade 73 that functions as a stray light suppression unit. 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 effectiveness 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.

[0026] In the modified example shown in Figure 10, the sensor cover 61 is further provided with a second protrusion 65 that functions as a stray light suppression unit within the area surrounded by the protrusion 63. This allows 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 to be 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. The higher the protrusion, the greater the effect that can be obtained.

[0027] A second embodiment of the present invention will be described with reference to Figures 11 and onward. 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 junction between the sensor cover 61 and the element substrate 55. Since the sensor cover 61 does not require highly precise alignment and is usually installed without alignment, 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.

[0028] The sensor cover 61 of this embodiment, shown in Figure 11, has a light-shielding wall 81 that protrudes downward and is located inside 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 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 56 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 as long as possible without causing interference with the element substrate 55 when the sensor cover 61 is attached.

[0029] The configuration of the stray light suppression unit, which suppresses stray light entering from between the sensor cover 61 and the element substrate 55, is not limited to the one described above. The modified element substrate 55A shown in Figure 12 has a light-absorbing section 82 that functions as a stray light suppression section 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 section and prevented from reaching the image sensor 56. The light-absorbing portion 82 can be made of black or dark-colored material, and can be formed by attaching a sheet-like material or by applying and curing a paste. If the surface of the light-absorbing portion 82 is excessively smooth, light that is not absorbed but reflected is more likely to occur, so it is preferable that the surface of the light-absorbing portion 82 has a moderate roughness. Depending on the material of the light-absorbing section 82, it is also possible to absorb the heat emitted by the image sensor 56, thereby suppressing the temperature rise of the image sensor during the operation of the camera 1. Examples of materials that can be expected to have this effect include graphite and silicone.

[0030] The embodiments shown in Figures 11 and 12 are examples in which the configuration that functions as a stray light suppression unit is located within the space enclosed 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 the groove 83, the peripheral wall 80 and the groove 83 function as stray light suppression parts 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.

[0031] 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 the configurations of the first embodiment, including modified versions.

[0032] 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.

[0033] For example, a stray light suppression unit may be provided in a part not mentioned in the above embodiment. In addition to 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, by providing a shade 91 that protrudes outward from the outer circumference, as in the modified lens barrel 51A shown in Figure 14, the shade 91 reduces the amount of light entering from the gap between the lens barrel 51 and the lens 52 and functions as a stray light suppression unit. 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. [Explanation of Symbols]

[0034] 1. Camera (distance imaging device) 2 First opening 3 Second opening 4. Light-blocking cover 10 cabinets 11 Main unit 12 Lid 13. Rubber gasket 20 Power supply boards 30 Main board 40 Imaging Unit 41 Light source substrate 42 VCSEL 50 Optical Units 51 Telescope Tube 52 lenses 53 Lens holder 53a Alignment groove 55 Element substrate 56 Image sensor 61 Sensor cover 63, 63A protrusion 65 Second protrusion 71 Adhesive 72 Light-blocking paste 73 Shades 81 Light-blocking wall 82 Light-absorbing section 100 Stray light suppression section

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, The joint between the lens holder and the sensor cover is provided with a stray light suppression unit to suppress the generation of stray light entering the optical unit. Optical unit.

2. The stray light suppression unit is composed of an alignment groove provided in the lens holder and a protrusion provided in the sensor cover that enters into the alignment groove. The optical unit according to claim 1.

3. The stray light suppression unit is further provided in the space surrounded by the sensor cover and the element substrate. The optical unit according to claim 1.

4. The optical unit comprises the optical unit according to any one of claims 1 to 3. Distance imaging device.

Images