Optical system and measurement device

Abstract

This optical system is provided with: a front group that is disposed on the object side and has a negative refractive power as a whole; and a rear group which is disposed closer to the sensor side than the position of the diaphragm and has a positive refractive power as a whole, and the optical system has a negative distortion aberration as a whole. The front group includes: a front group first lens disposed on the object side and composed of a resin lens having a negative refractive power; and a front-group second lens that is disposed closest to the diaphragm and is composed of a resin lens having an aspheric surface on the sensor side. The rear group is provided with: a rear group first lens which is disposed closest to the diaphragm and which is composed of a glass lens having a positive refractive power; and a rear-group second lens that is disposed closest to the sensor side and is composed of a resin lens having a positive refractive power. In the front group second lens, a surface on the object side is configured to be concave, and a surface on the sensor side is configured to be convex.

Description

Technical Field

[0001] The present invention relates to an optical system and a measuring device. Background Art

[0002] Patent Document 1 describes a retrofocus optical system. Patent Document 2 describes an optical radar (LIDAR: Light Detection and Ranging / Laser Imaging Detection and Ranging) having an athermalized optical system.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: WO2019-073744

[0006] Patent Document 2: Japanese Patent Application Publication No. 2021-124725 Summary of the Invention

[0007] (1) Technical issues to be resolved

[0008] Measuring devices such as optical radars preferably have a wide field of view. However, in optical systems with a wide field of view, the amount of peripheral light decreases according to the fourth-power cosine law (peripheral glare reduction). Using an optical system with such peripheral glare reduction in a measuring device can reduce the detection range at the periphery of the field of view.

[0009] Additionally, because resin lenses are lighter than glass lenses, they are sometimes used to reduce the weight of optical systems. However, since measurement devices such as optical radar are vehicle-mounted, they must maintain performance over a wide temperature range. Therefore, when using resin lenses in optical systems, temperature compensation is necessary.

[0010] The object of the present invention is to provide a novel optical system which takes into account the following two aspects: a wide field of view, brightening the peripheral light quantity; and temperature compensation while using a resin lens.

[0011] (2) Technical solution

[0012] In order to achieve the above-mentioned object, one embodiment of the present invention is the following optical system, which is an optical system of a measuring device that causes a sensor to receive reflected light, comprising: a front group, which is arranged on the object side and has negative optical power as a whole; and a rear group, which is arranged on the sensor side relative to the aperture and has positive optical power as a whole, the optical system having negative distortion as a whole, the front group comprising: a front-group first lens, which is arranged on the object side and consists of a resin lens with negative optical power; and a front-group second lens, which is arranged on the side closest to the aperture and consists of a resin lens whose sensor-side surface is aspherical, the rear group comprising: a rear-group first lens, which is arranged on the side closest to the aperture and consists of a glass lens with positive optical power; and a rear-group second lens, which is arranged on the side closest to the sensor and consists of a resin lens with positive optical power, the object-side surface of the front-group second lens being concave and the sensor-side surface being convex.

[0013] Furthermore, the technical problems disclosed in the present application and their solutions are clarified through the detailed description and the accompanying drawings.

[0014] (3) Beneficial effects

[0015] According to the present invention, an optical system that achieves both the following two aspects: a wide field of view, bright peripheral light intensity, and temperature compensation while using a resin lens can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is an explanatory diagram of the basic structure of the optical system 2 according to this embodiment.

[0017] Figure 2 1 and 2 are aberration diagrams showing distortion of the optical system 2 .

[0018] Figure 3 It is an explanatory diagram showing the area where the on-axis light beam and the off-axis light beam pass through the lens L1.

[0019] Figure 4 This is a table showing an example of design data of the optical system 2 according to this embodiment.

[0020] Figure 5A Yes Figure 4 A graph showing the amount of light in the optical system 2 is shown. Figure 5B This is a graph of a comparative example, and is a graph expressing the fourth-power cosine law.

[0021] Figure 6A to Figure 6C Yes Figure 4 The MTF graph of the optical system 2 at various temperatures is shown.

[0022] Figure 7This is a table showing another example of the design data of the optical system 2 according to this embodiment.

[0023] Figure 8 is with Figure 7 This is an explanatory diagram of the optical system corresponding to the design data.

[0024] Figure 9 Yes Figure 7 as well as Figure 8 Aberration diagram showing distortion aberration of the optical system shown.

[0025] Figure 10 Yes Figure 7 A graph showing the amount of light in the optical system 2 is shown.

[0026] Figure 11A to Figure 11C Yes Figure 7 The MTF graph of the optical system 2 at various temperatures is shown.

[0027] Figure 12 It is an explanatory diagram of the overall structure of the measuring device 1.

[0028] Figure 13 1 is a schematic explanatory diagram of the measuring device 1 .

[0029] Figure 14 It is an explanatory diagram of an example in which the measurement device 1 is mounted on a vehicle. DETAILED DESCRIPTION

[0030] <Cross-reference of related applications>

[0031] This application claims priority based on Japanese invention patent application No. 2023-036638 filed on March 9, 2023, and incorporates the contents thereof.

[0032] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same or similar structures are sometimes given common reference numerals and repeated descriptions are omitted.

[0033] ===Implementation Method===

[0034] About the optical system

[0035] Figure 1 It is an explanatory diagram of the basic structure of the optical system 2 according to this embodiment.

[0036] The optical system 2 of this embodiment includes a front group 2A and a rear group 2B. The optical system 2 has positive refractive power (positive refractive power) as a whole. A sensor 3 is arranged on the image plane of the optical system 2. The image plane side is sometimes referred to as the "sensor side."

[0037] Front group 2A is a lens group positioned on the object side of optical system 2. Front group 2A as a whole has negative refractive power (negative refractive power). For example, front group 2A is configured to capture light at a relatively wide viewing angle, such as approximately 120 degrees.

[0038] The rear lens group 2B is a lens group disposed on the sensor side of the optical system 2. The rear lens group 2B has positive refractive power (positive refractive power) as a whole.

[0039] The sensor-side surface of lens L2 in the figure functions as an aperture. The figure shows that at the position on the sensor-side surface of lens L2, the principal ray of the off-axis beam intersects the optical axis. Furthermore, the figure shows that at the upper edge of the sensor-side surface of lens L2, the upper line of the on-axis beam intersects the upper line of the off-axis beam, and at the lower edge of the sensor-side surface of lens L2, the lower line of the on-axis beam intersects the lower line of the off-axis beam. Thus, the figure shows that the sensor-side spherical surface of lens L2 functions as an aperture. The position of the aperture is not limited to the sensor-side surface of lens L2. For example, an aperture stop may be provided between the front lens group 2A and the rear lens group 2B.

[0040] In the optical system 2 of this embodiment, the front lens group 2A, located on the object side relative to the aperture stop, has negative refractive power, while the rear lens group 2B, located on the sensor side relative to the aperture stop, has positive refractive power, resulting in a so-called retrofocus structure. As will be described later, the optical system 2 of this embodiment has negative distortion.

[0041] The front group 2A includes lens L1 and lens L2. The front group 2A is composed of lens L1 and lens L2 arranged in this order from the object side. Lens L1 corresponds to the first lens of the front group, and lens L2 corresponds to the second lens of the front group.

[0042] Lens L1 is a negative refractive power lens located on the object side of front group 2A. It is a meniscus lens with its object side convex, designed to capture light at a relatively wide angle of view. Lens L1 is made of a resin lens.

[0043] Since lens L1 is made of a resin lens, it is more susceptible to temperature changes than a glass lens. However, lens L1 is configured to offset the effects of temperature changes together with lens L5 (temperature compensation). This will be described later.

[0044] Furthermore, lens L1 preferably has an aspheric surface. This allows lens L1 to be configured to sharply bend wide-angle incident light along the optical axis while suppressing aberrations. Constructing lens L1 from a resin lens also facilitates the formation of an aspheric surface on lens L1. However, lens L1 does not necessarily need to have an aspheric surface.

[0045] Lens L2 is the lens closest to the aperture stop in the front group 2A. As described above, the sensor-side surface of lens L2 functions as a stop, making it the lens closest to the aperture stop. Lens L2 is the lens closest to the object in the front group 2A. The sensor-side surface of lens L2 is aspherical. Because lens L2 is the lens closest to the aperture stop, on-axis and off-axis light beams overlap on the sensor-side surface of lens L2, making this sensor-side surface (aspherical) ideal for correcting spherical aberration. Since the sensor-side surface of lens L2 functions as a stop, on-axis and off-axis light beams overlap on the sensor-side surface of lens L2, making it particularly suitable for correcting spherical aberration. However, even when an aperture stop is provided between the front lens group 2A and the rear lens group 2B, since the on-axis and off-axis light beams primarily overlap on the sensor-side surface of lens L2, the sensor-side surface of lens L2 is also suitable for correcting spherical aberration. Lens L2 is composed of a resin lens. This also facilitates the formation of an aspherical surface on lens L2.

[0046] Because lens L2 is made of a resin lens, it is more susceptible to temperature effects than glass lenses. However, by configuring lens L2 as a meniscus lens with a concave object-side shape and a convex sensor-side shape, the effects of temperature changes in lens L2 on optical system 2 are minimized. Furthermore, by configuring lens L2 as a resin lens, lens L2 is minimized from interfering with temperature compensation (described later) performed by lenses L1 and L5.

[0047] The rear group 2B includes lens L3, lens L4, and lens L5. The rear group 2B is composed of lens L3, lens L4, and lens L5, arranged in this order from the object side. Lens L3 corresponds to the first lens of the rear group, and lens L5 corresponds to the second lens of the rear group.

[0048] Lens L3 is the lens closest to the aperture stop in the rear lens group 2B. In other words, lens L3 is the lens closest to the object in the rear lens group 2B. Lens L3 is a glass lens with positive refractive power. By placing a glass lens with relatively strong positive refractive power closest to the aperture stop, changes in the refractive power of the optical system 2 with temperature fluctuations are suppressed.

[0049] Lens L4 and lens L5 are lenses arranged on the sensor side relative to lens L3. Lens L4 and lens L5 have positive refractive power as a whole.

[0050] Lens L5 is the lens closest to the sensor in the rear lens group 2B. It is a resin lens with positive refractive power. Lens L5 performs temperature compensation together with lens L1. Specifically, lens L1, which is furthest from the object when viewed from the aperture, is a resin lens with negative refractive power, while lens L5, which is furthest from the sensor when viewed from the aperture, is a resin lens with positive refractive power. This allows temperature compensation to offset the effects of temperature changes. In other words, passive temperature compensation is performed by lenses L1 and L5 at both ends of the optical system 2.

[0051] The sensor-side surface of lens L5 is aspherical. Because lens L5 is positioned closest to the sensor, the on-axis and off-axis beams are separated at lens L5. This makes the sensor-side surface of lens L5 suitable for correcting off-axis aberrations by varying the curvature of the spherical surface of lens L5 according to the distance from the optical axis. Not only the sensor-side surface of lens L5, but also the object-side surface can be aspherical. Constructing lens L5 from a resin lens also facilitates the formation of an aspherical surface on lens L5.

[0052] Lens L4 is composed of a glass lens with positive refractive power. Thus, the required refractive power is provided by lens L4 and lens L5 as a whole, while suppressing the influence of temperature changes on optical system 2 (rear group 2B). In addition, if the refractive power required by the lens group closer to the sensor than lens L3 can be provided by lens L5 alone, lens L4 may not be arranged between lens L3 and lens L5 (described later; refer to Figure 8 However, because lens L5 is constrained by the need to perform temperature compensation along with lens L1, the design of lens L5 is simplified by providing lens L4. Therefore, it is preferable to use lens L4 to supplement the refractive power required by the lens group closer to the sensor than lens L3.

[0053] Figure 2 1 and 2 are aberration diagrams showing distortion of the optical system 2. The vertical axis of the aberration diagram in the figure represents the angle of view (unit: degree; half angle of view), and the horizontal axis represents the distortion D (unit: %; distortion).

[0054] When the ideal image height of a lens without distortion is y and the actual image height of a lens with distortion is y′, the distortion D (unit: %) can be expressed as follows.

[0055] D = {(y'-y) / y} × 100

[0056] Here, when the focal length of the lens is f and the angle of light is θ, the image heights y and y′ can be expressed as follows.

[0057] y=f×tanθ

[0058] y'={1+(D / 100)}×f×tanθ

[0059] When the optical system 2 has negative distortion D, the distortion magnification β (=1+(D / 100)) is less than 1 (β<1). Therefore, when the optical system 2 has negative distortion D, pixels on the periphery of the sensor 3 (pixels farther from the optical axis) can receive light incident from a wider angle than pixels at the center of the sensor 3 (pixels on or near the optical axis).

[0060] As described above, in this embodiment, the optical system 2 is configured to have negative distortion. In addition, in this embodiment, since the front group 2A has negative refractive power, the front group 2A changes the direction of light so that it approaches the optical axis as it approaches the aperture stop (see FIG. Figure 1 On the other hand, since the rear group 2B has positive refractive power, the rear group 2B changes the direction of light so that it approaches the optical axis as it gets closer to the sensor 3 (see Figure 1 The main ray of the off-axis beam from the rear lens group 2B is also reflected in the front lens group 2A). In other words, the front lens group 2A and rear lens group 2B each act to bring the sensor's main ray of the off-axis beam closer to the optical axis. This means that the front lens group 2A and rear lens group 2B act to reduce the aforementioned image height y', which in turn means that the front lens group 2A and rear lens group 2B act to make the distortion D negative.

[0061] That is, in this embodiment, in order to suppress peripheral vignetting, an optical system 2 having negative distortion as a whole is employed. Furthermore, in this embodiment, in order to provide the optical system 2 with negative distortion as a whole, an optical system 2 is employed that includes a front optical group 2A having negative power as a whole and a rear optical group 2B having positive power as a whole.

[0062] In addition, in this embodiment, Figure 2 (or the following Figure 9 ), the optical system 2 is configured so that the absolute value of distortion D increases toward the periphery (the farther the sensor 3 receives light, the larger the angle of the incident light). This can suppress the increase in glare toward the periphery due to the fourth-power cosine law.

[0063] In this embodiment, the absolute value of distortion for light incident at 50 degrees is set to 10% or greater. In this embodiment, the optical system 2 is designed to have negative distortion to suppress peripheral bleed. Furthermore, since wide-angle lenses used in typical cameras (imaging devices) are designed to suppress distortion, the distortion of the optical system 2 in this embodiment is relatively large compared to typical wide-angle lenses used in cameras.

[0064] Figure 3 It is an explanatory diagram showing the area where the on-axis light beam and the off-axis light beam pass through the lens L1.

[0065] The large outer circle, indicated by a solid line in the figure, represents the size of lens L1. The central shaded area S1 in the figure represents the area where the on-axis beam passes through lens L1. Area S1 is circular. The lower shaded area S2 in the figure represents the area where the off-axis beam passes through lens L1. Area S2 is elliptical.

[0066] In this embodiment, the area S2 where the off-axis light beam passes through the lens L1 is larger than the area S1 where the on-axis light beam passes through the lens L1. This makes it possible to thicken the off-axis light beam and suppress peripheral glare.

[0067] Furthermore, in this embodiment, the length of region S2 in the radial direction is greater than the length (diameter) of region S1 in the radial direction. Furthermore, the ratio of the length of region S2 in the radial direction to the diameter of region S1 is greater than the ratio of the length of region S2 in the concentric direction to the diameter of region S1. This means that the angle of view of the off-axis beam is wider than that of the on-axis beam. In other words, in this embodiment, front group 2A is configured so that the angle of view of the off-axis beam is wider than that of the on-axis beam. Consequently, optical system 2 (front group 2A) is configured so that region S2 is larger than region S1.

[0068] Furthermore, in this embodiment, to make area S2 larger than area S1, the front group 2A is composed of lens L1 having negative refractive power and lens L2 having a concave object-side shape and a convex sensor-side shape. The sensor-side surface of lens L2 functions as a stop. Furthermore, if a planar aperture stop were provided between the front group 2A and the rear group 2B instead of using the sensor-side surface of lens L2 as the stop, off-axis light beams obliquely passing through the stop would be narrowed, causing peripheral bleaching. In contrast, in this embodiment, by configuring the negative refractive power of the front group 2A closer to the object than the stop (the object-side surface of lens L1, the sensor-side surface of lens L1, and the object-side surface of lens L2), and by making the sensor-side surface of lens L2 functioning as the stop convex, the off-axis light beams passing through the stop can be broadened.

[0069] Furthermore, the lower line of the off-axis light beam moves farther from the optical axis as it approaches the aperture stop in lens L2. This inclusion of light rays farther from the optical axis as they approach the aperture stop in the light beam of front group 2A (the light beam whose principal ray is located below the optical axis) also contributes to thickening the off-axis light beam. Furthermore, by configuring the front group 2A with negative power on the object side relative to the aperture stop (the object-side surface of lens L1, the sensor-side surface of lens L1, and the object-side surface of lens L2), and by making the sensor-side surface of lens L2, which functions as the aperture stop, convex, the front group 2A is configured so that light rays farther from the optical axis as they approach the aperture stop are included in the light beam of front group 2A, thereby thickening the off-axis light beam that passes through the aperture stop.

[0070] Furthermore, in this embodiment, the sensor-side surface of lens L2 is convex, which allows the diameter of lens L3 to be reduced. Specifically, in this embodiment, by making the sensor-side surface of lens L2 convex, the light beam passing through the aperture can be thickened while suppressing the increase in lens diameter.

[0071] <About Examples>

[0072] Figure 4 This is an example of design data of the optical system 2 of this embodiment. Figure 1 The optical system 2 shown is Figure 4 The design data corresponds to Figure 2 The distortion diagram shown is also consistent with Figure 4 )

[0073] Figure 4 Surface numbers "1" to "4" correspond to the object-side surface of lens L1, the sensor-side surface of lens L1, the object-side surface of lens L2, and the sensor-side surface of lens L2, respectively. Surface number "4" functions as an aperture. Figure 4 Surface numbers "5" through "10" correspond to the object-side surface of lens L3, the sensor-side surface of lens L3, the object-side surface of lens L4, the sensor-side surface of lens L4, the object-side surface of lens L5, and the sensor-side surface of lens L5, respectively. The units of curvature radius and thickness are [mm]. Lenses L1, L2, and L5 are resin lenses (Optical polyester resin OKP-1, manufactured by Osaka Gas Chemical Co., Ltd.), while lenses L3 and L4 are glass lenses (Optical glass TAFD40, manufactured by HOYA Corporation).

[0074] The sag value z (unit: mm) for the aspherical shapes of surface numbers "1" to "4," "9," and "10" is expressed by the following formula. In this formula, r represents the height from the optical axis within the surface, c is the inverse of the radius of curvature, k is the conic constant, and An is the coefficient of r raised to the power of 2n.

[0075] [Formula 1]

[0076]

[0077] Figure 5A Yes Figure 4 A graph showing the amount of light in the optical system 2 is shown. Figure 5B This is a graph of a comparative example, illustrating the fourth-power cosine law. The horizontal axis represents the half-angle of view (unit: degrees), and the vertical axis represents the amount of light on the image plane (ratio based on the assumption that the amount of light on the optical axis is 1). For example, the amount of light at 60 degrees is 0.0625 (0.5 to the fourth power) in the comparative example, while it is approximately 0.5 in the present embodiment. As can be seen, the optical system 2 of the present embodiment suppresses peripheral fading compared to the comparative example. Specifically, the negative distortion of the optical system 2 (and, by making the off-axis beam thicker than the on-axis beam) can suppress peripheral fading.

[0078] Figure 6A to Figure 6C Yes Figure 4 The MTF graph of the optical system 2 at various temperatures is shown. Figure 6A This is a graph showing the MTF at -40°C. Figure 6B This is a graph showing the MTF at 25°C. Figure 6C This is a graph showing the MTF at 85°C. The horizontal axis of the graph represents the half-field angle (unit: degrees), and the vertical axis represents the MTF value (contrast value). The bold curve represents the curve corresponding to a spatial frequency of 10 lines / mm, and the thin curve represents the curve corresponding to a spatial frequency of 30 lines / mm. The solid curve represents the curve in the M direction (meridional direction; concentric circles), and the dashed curve represents the curve in the S direction (radial direction; radial direction). Focusing on the bold curve (the curve corresponding to a spatial frequency of 10 lines / mm), the MTF value remains above 0.5 at all temperatures. This shows that the optical system 2 of this embodiment, even when using resin lenses, can maintain performance over a wide temperature range, from -40°C to 85°C. Furthermore, the optical system 2 of this embodiment performs temperature compensation using lenses L1 and L5, and lens L2 is a meniscus lens, thereby preventing any impairment of temperature compensation.

[0079] Figure 7 This is another example of the design data of the optical system 2 in this embodiment. Figure 8is with Figure 7 This is an explanatory diagram of the optical system corresponding to the design data. Figure 9 Yes Figure 7 as well as Figure 8 Aberration diagram showing distortion aberration of the optical system shown.

[0080] and Figure 1 as well as Figure 4 The optical system 2 shown is similarly Figure 7 as well as Figure 8 The optical system 2 shown includes a front group 2A (lens L1 and lens L2) having negative refractive power as a whole and a rear group 2B (lens L3 and lens L5) having positive refractive power as a whole, and the optical system as a whole has negative distortion. Figure 7 as well as Figure 8 The optical system 2 shown is Figure 1 as well as Figure 4 The optical system 2 shown is different in that the lens L4 is not arranged between the lens L3 and the lens L5.

[0081] Figure 7 Surface numbers "1" to "4" correspond to the object-side surface of lens L1, the sensor-side surface of lens L1, the object-side surface of lens L2, and the sensor-side surface of lens L2, respectively. Surface number "4" functions as an aperture. Figure 7 Surface numbers "5" through "8" correspond to the object-side surface of lens L3, the sensor-side surface of lens L3, the object-side surface of lens L5, and the sensor-side surface of lens L5, respectively. The units of curvature radius and thickness are [mm]. Lenses L1, L2, and L5 are resin lenses (Optical polyester resin OKP-1, manufactured by Osaka Gas Chemical Co., Ltd.), while lens L3 is a glass lens (Optical glass TAFD40, manufactured by HOYA Corporation).

[0082] Figure 10 Yes Figure 7 The light quantity curve diagram of the optical system 2 is shown. Figure 7 Similarly, in the optical system 2 shown, for example, the light quantity at 60 degrees is about 0.5. Figure 7 In the optical system 2 shown in FIG. 1 , the same as in the comparative example (refer to FIG. Figure 5B ). That is, even without lens L4 between lens L3 and lens L5, peripheral vignetting can be suppressed by having negative distortion in optical system 2 (and by making off-axis beams thicker than on-axis beams).

[0083] Figure 11A to Figure 11C Yes Figure 7 The MTF graph of the optical system 2 at various temperatures is shown. Figure 11A This is a graph showing the MTF at -40°C. Figure 11B This is a graph showing the MTF at 25°C. Figure 11C This is a graph showing the MTF at 85°C. If we focus on the thick line (the curve corresponding to the spatial frequency of 10 lines / mm), the MTF value remains above 0.5 at any temperature. Figure 7 Even in the optical system 2 shown in FIG. 1 , even when a resin lens is used, the performance is maintained in a wide temperature range from -40°C to 85°C. Figure 7 In the optical system 2 shown, temperature compensation is similarly performed by the lens L1 and the lens L5 , and the lens L2 is set as a meniscus lens, thereby suppressing the temperature compensation from being hindered.

[0084] also, Figure 4 as well as Figure 7 The design data shown is data showing an example of the optical system 2 of this embodiment. Figure 4 as well as Figure 7 The design data of the optical system is shown.

[0085] <About the measuring device>

[0086] Figure 12 It is an explanatory diagram of the overall structure of the measuring device 1. Figure 13 1 is a schematic explanatory diagram of the measuring device 1 .

[0087] The measuring device measures the distance to an object 90. The measuring device 1 functions as a so-called LiDAR (Light Detection and Ranging) system. The measuring device 1 emits measuring light, detects the light reflected from the surface of the object 90, and measures the distance to the object 90. For example, the measuring device 1 measures the distance to the object 90 using a TOF (Time of Flight) method by measuring the time from emission of the measuring light to reception of the reflected light. The measuring device 1 includes an irradiation unit 10, a light receiving unit 20, and a control unit 30.

[0088] The irradiation unit 10 is an irradiation device that irradiates the measurement light toward the object 90. The irradiation unit 10 irradiates the measurement area 50 (see FIG. 5 ) at a predetermined viewing angle. Figure 13) irradiates measurement light. The irradiation unit 10 includes a light emitting unit 12 and a light projection optical system 14. The light emitting unit 12 is a component that emits light (a light source). The light projection optical system 14 is an optical system that directs the light emitted from the light emitting unit 12 toward the measurement area 50. The irradiation unit 10 can be configured to irradiate the entire measurement area 50 with light. Alternatively, the irradiation unit 10 can be configured to irradiate the measurement area 50 with light in a scanning manner.

[0089] The light receiving unit 20 receives the reflected light from the object 90. The light receiving unit 20 receives the reflected light from the measurement area 50 (refer to Figure 13 ) reflected light. The light receiving unit 20 includes a light receiving sensor 22 and a light receiving optical system 24. The light receiving sensor 22 includes a plurality of pixels 221 arranged two-dimensionally. For example, in the case of a VGA light receiving sensor 22, 480×640 pixels 221 are arranged two-dimensionally. Each pixel 221 outputs a signal (light receiving data) corresponding to the amount of light received. The light receiving optical system 24 is an optical system that enables the light receiving unit 20 to receive the reflected light from the measurement area 50. Here, the light receiving optical system 24 is composed of Figure 1 (or Figure 8 ) is composed of the optical system 2 shown in FIG. In addition, the light receiving sensor 22 is equivalent to Figure 1 (or Figure 8 ) is arranged on the image plane of the light-receiving optical system 24. Each pixel 221 of the light-receiving sensor 22 is associated with a predetermined area of ​​the measurement region 50 via the light-receiving optical system 24. A pixel 221 of the light-receiving sensor 22 receives light (reflected light) from the corresponding area of ​​the measurement region 50 via the light-receiving optical system 24.

[0090] The control unit 30 is responsible for controlling the measuring device 1. The control unit 30 controls the irradiation unit 10 and controls the light irradiated from the irradiation unit 10. In addition, the control unit 30 measures the distance to the object 90 based on the output result of the light receiving unit 20. The control unit 30 has a computing device and a storage device, which are not shown in the figure. The computing device is, for example, a computing processing device such as a CPU and a GPU. A part of the computing device can also be composed of an analog computing circuit. The storage device is composed of a main storage device and an auxiliary storage device, and is a device for storing programs and data. The various processes for measuring the distance to the object 90 are performed by executing the program stored in the storage device through the computing device. Figure 12 The functional blocks of various processes are shown in FIG.

[0091] The control unit 30 includes a setting unit 32, a timing control unit 34, and a distance measuring unit 36. The setting unit 32 performs various settings. The timing control unit 34 controls the processing timing of each unit. For example, the timing control unit 34 controls the timing of light emission from the light emitting unit 12. The distance measuring unit 36 ​​measures the distance to the object 90. The distance measuring unit 36 ​​includes a signal processing unit 362, a time detection unit 364, and a distance calculation unit 366. The signal processing unit 362 processes the output signal (light reception data) of the light receiving sensor 22. The time detection unit 364 detects the flight time of light (the time from light irradiation to the arrival of reflected light). The distance calculation unit 366 calculates the distance to the object 90.

[0092] Figure 14 This is an explanatory diagram of an example in which the measuring device 1 is mounted on a vehicle. As shown in the figure, when the measuring device 1 is mounted on a vehicle, it is desired to measure distance with a wide field of view. In addition, when the measuring device 1 is mounted on a vehicle, it is desired to be lightweight and maintain performance over a wide temperature range. In this regard, in this embodiment, the light receiving optical system 24 of the measuring device 1 is composed of Figure 1 (or Figure 8 ). This configuration of the optical system 2 shown in FIG. This suppresses a decrease in the amount of light received by pixels surrounding the light-receiving sensor 22, thereby minimizing a decrease in the detection distance around the field of view (the region corresponding to the pixels surrounding the light-receiving sensor 22). Furthermore, the use of resin glass enables weight reduction while maintaining performance over a wide temperature range. Thus, the optical system 2 of this embodiment is particularly effective as the light-receiving optical system 24 of the measuring device 1.

[0093] Summary

[0094] As described above, the optical system 2 of this embodiment comprises a front lens group 2A with negative refractive power and a rear lens group 2B with positive refractive power, resulting in negative distortion as a whole. This allows for a wide field of view and bright peripheral light intensity (wide angles with suppressed peripheral vignetting). Furthermore, the front lens group 2A comprises lens L1 (equivalent to the first lens in the front group) and lens L2 (equivalent to the second lens in the front group), both made of resin lenses. The rear lens group 2B comprises lens L3 (equivalent to the first lens in the rear group) and lens L5 (equivalent to the second lens in the rear group), both made of glass lenses. This mixture of resin and glass lenses achieves a lighter weight compared to a system composed entirely of glass lenses. While the properties of resin glass are more susceptible to temperature fluctuations than glass lenses, in this embodiment, by placing lens L1 with negative refractive power and lens L5 with positive refractive power at both ends of the optical system 2, passive temperature compensation is achieved. Furthermore, because lens L3 (equivalent to the first lens in the rear group), which is positioned closest to the aperture and has positive refractive power, is a glass lens, changes in the characteristics of optical system 2 due to temperature fluctuations are minimized. Furthermore, although lens L2 (equivalent to the second lens in the front group) is constructed from a resin lens due to its aspherical surface, its concave object-side surface and convex sensor-side surface minimize the effects of temperature fluctuations on optical system 2, preventing lens L2 from hindering temperature compensation by lenses L1 and L5. Consequently, the optical system 2 of this embodiment achieves both a wide field of view, brightening the peripheral light intensity, and temperature compensation while employing a resin lens.

[0095] In addition, if Figure 2 as well as Figure 9 As shown in FIG. 1 , it is preferable to construct the optical system 2 so that the absolute value of the distortion aberration increases toward the periphery. Figure 5B The amount of light in the peripheral area shown decreases according to the fourth power cosine law (see Figure 5A 、 Figure 10 ). In addition, Figure 2 as well as Figure 9 In the example shown, the absolute value of the distortion aberration for light incident at 50 degrees is set to 10% or more, but the distortion aberration is not limited to Figure 2 、 Figure 9 Distortion shown.

[0096] In addition, if Figure 3As shown, it is preferable that the area S2 where the off-axis light beam passes through lens L1 is larger than the area S1 where the on-axis light beam passes through lens L1. This allows the off-axis light beam to be thicker, thus suppressing peripheral glare. Furthermore, even if the optical system 2 is not configured so that area S2 is larger than area S1, as long as the optical system 2 has negative distortion, the reduction in peripheral light intensity according to the fourth power cosine law can be suppressed. However, configuring the optical system 2 so that the optical system 2 has negative distortion and area S2 is larger than area S1 is particularly advantageous because it can synergistically suppress peripheral glare.

[0097] Furthermore, it is preferable that the lens L1 (corresponding to the first lens in the front group) has an aspherical surface. However, the lens L1 does not necessarily have to have an aspherical surface.

[0098] Furthermore, it is preferable that the sensor-facing surface of lens L2 (equivalent to the second lens in the front group) function as a stop. This eliminates the need for a stop mechanism between the front lens group 2A and the rear lens group 2B. Furthermore, since the sensor-facing surface of lens L2, which functions as a stop, is convex, it also achieves the effect of reducing the diameter of lens L3.

[0099] When the sensor-side surface of lens L2 (equivalent to the second lens element in the front group) functions as a stop, it is preferable that the sensor-side surface of lens L2 be configured as an aspherical surface for correcting spherical aberration. This is because, when the sensor-side surface of lens L2 (equivalent to the second lens element in the front group) functions as a stop, on-axis and off-axis light beams overlap on the sensor-side surface of lens L2, making the sensor-side surface of lens L2 particularly suitable for correcting spherical aberration. However, the sensor-side surface of lens L2 does not necessarily need to be configured as an aspherical surface for correcting spherical aberration.

[0100] Furthermore, it is preferable to place a glass lens L4 between lens L3 (equivalent to the first lens in the rear group) and lens L5 (equivalent to the second lens in the rear group). This provides the refractive power required by the lens group closer to the sensor than lens L3 while also minimizing the effects of temperature changes on optical system 2. However, optical system 2 does not necessarily need to include lens L4.

[0101] Furthermore, it is preferable that lens L5 (equivalent to the second lens in the rear group) have an aspherical surface that corrects off-axis aberrations. This is because lens L5 is positioned closest to the sensor, and thus, the on-axis and off-axis beams are separated at lens L5, making it suitable to correct off-axis aberrations within lens L5. However, lens L5 does not necessarily need to have an aspherical surface that corrects off-axis aberrations.

[0102] As described above, the measuring device 1 of this embodiment includes the aforementioned optical system 2 as the light-receiving optical system 24. This prevents a decrease in the amount of light received by pixels surrounding the light-receiving sensor 22 (sensor 3), thereby minimizing a decrease in the detection distance around the periphery of the field of view (the region corresponding to the pixels surrounding the light-receiving sensor 22). Furthermore, the use of resin glass enables weight reduction and maintains performance over a wide temperature range. Furthermore, the measuring device 1 of this embodiment is particularly advantageous when mounted on a vehicle. However, the measuring device 1 does not necessarily need to be mounted on a vehicle.

[0103] While the embodiments of the present invention have been described in detail above, the present invention is not limited to the aforementioned embodiments and encompasses various variations. Furthermore, the aforementioned embodiments describe the configurations in detail for easy understanding of the present invention and are not necessarily limited to embodiments having all of the configurations described. Furthermore, with respect to portions of the configurations of the aforementioned embodiments, other configurations may be added, deleted, or replaced.

[0104] Description of reference numerals:

[0105] L1: Lens (first lens of the front group); L2: Lens (second lens of the front group); L3: Lens (first lens of the rear group); L4: Lens; L5: Lens (second lens of the rear group); 1: Measuring device; 2: Optical system; 2A: Front group; 2B: Rear group; 3: Sensor; 10: Illuminating unit; 12: Light-emitting unit; 14: Optical system for projecting light; 20: Light-receiving unit; 22: Light-receiving sensor (sensor); 24: Optical system for receiving light (optical system); 50: Measuring area; 90: Object.

Claims

1. An optical system of a measuring device that causes a sensor to receive reflected light, comprising: A front group, which is arranged on the object side and has negative refractive power as a whole; and The rear group is located closer to the sensor than the aperture, and has positive refractive power as a whole. The optical system as a whole has negative distortion aberration, The front group has: a front first lens group, which is arranged on the object side and is composed of a resin lens having negative refractive power; and The second lens in the front group is located closest to the aperture and is composed of a resin lens with an aspherical surface facing the sensor. The rear group has: a rear first lens group, which is located closest to the aperture stop and is composed of a glass lens having positive refractive power; and The second lens in the rear group is located closest to the sensor and is composed of a resin lens with positive refractive power. The second lens in the front group has a concave surface on the object side and a convex surface on the sensor side.

2. The optical system according to claim 1, wherein: The absolute value of the distortion aberration is set to increase toward the periphery.

3. The optical system according to claim 2, wherein: The absolute value of the distortion aberration at 50 degrees is greater than 10%.

4. The optical system according to any one of claims 1 to 3, wherein: An area where an off-axis light beam passes through the front-group first lens is larger than an area where an on-axis light beam passes through the front-group first lens.

5. The optical system according to any one of claims 1 to 3, wherein: The front first lens group has an aspherical surface.

6. The optical system according to any one of claims 1 to 3, characterized in that The sensor-side surface of the front second lens group functions as a stop.

7. The optical system according to claim 6, wherein: The sensor-side surface of the second lens in the front group is configured as an aspherical surface that corrects spherical aberration.

8. The optical system according to any one of claims 1 to 3, wherein: A glass lens is disposed between the first rear lens group and the second rear lens group.

9. The optical system according to any one of claims 1 to 3, wherein: The second lens in the rear group has an aspherical surface.

10. The optical system according to claim 9, wherein: The second lens in the rear group has an aspherical surface for correcting off-axis aberrations.

11. A measuring device comprising: an irradiation portion that irradiates light; and a light receiving portion that receives reflected light from an object after the light irradiated from the irradiating portion is reflected; The light receiving unit comprises: a sensor configured with a plurality of pixels for detecting the reflected light; and a light receiving optical system that causes the sensor to receive the reflected light, The light receiving optical system comprises: A front group, which is arranged on the object side and has negative refractive power as a whole; and The rear group is located closer to the sensor than the aperture, and has positive refractive power as a whole. The light receiving optical system as a whole has negative distortion aberration, The front group has: The first lens element of the front group is arranged on the object side and is composed of a resin lens with negative refractive power; The second lens in the front group is located closest to the aperture and is composed of a resin lens with an aspherical surface facing the sensor. The rear group has: a rear first lens group, which is located closest to the aperture stop and is composed of a glass lens having positive refractive power; and The second lens in the rear group is located closest to the sensor and is composed of a resin lens with positive refractive power. The second lens in the front group has a concave surface on the object side and a convex surface on the sensor side.

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