Ultrathin DMS monitoring optical system

Abstract

The utility model discloses an ultrathin DMS monitoring optical system, which relates to the technical field of optical systems and vehicle-mounted imaging devices and sequentially comprises a diaphragm, a first lens, a second lens, a third lens, a fourth lens, an optical filter, protective glass and an image plane from an object plane to an image plane along an optical axis. The object plane side of the first lens is a convex surface, and the image plane side is a convex surface. The object surface side of the second lens is a convex surface, and the image surface side is a concave surface; the object plane side of the third lens is a concave surface, and the image plane side is a convex surface; the object plane side of the fourth lens is a convex surface, and the image plane side is a concave surface. According to the ultra-thin DMS monitoring optical system, four lenses are arranged, the defects that an existing vehicle-mounted DMS lens is too large in size, high in cost, difficult to be suitable for high and low temperature changing environments and the like are effectively overcome through the lens surface type design and the mode that the positive lens and the negative lens are matched, and the ultra-thin DMS monitoring optical system has the advantages of being low in cost, small in size, athermalized and free of distortion.

Description

Technical Field

[0001] The utility model relates to the technical field of optical systems and vehicle-mounted imaging devices, in particular to an ultra-thin DMS monitoring optical system and an imaging device. Background Art

[0002] At present, the DMS system of visual sensors has become one of the mainstream technologies in the field of vehicle-mounted imaging. The DMS system (Driver Monitor System) can realize functions such as driver fatigue monitoring, attention monitoring, dangerous driving behavior monitoring and driver identity recognition. It is an important sensor for intelligent driving and one of the core components for realizing intelligent cockpit visual interaction. By installing visual cameras and infrared cameras in the car, using eye tracking, facial recognition and other technologies to monitor the driver's eyes, head status and hand movements, it can be determined whether he has fatigue driving or dangerous driving behaviors, avoid safety hazards in the process of driving, and reduce the possibility of traffic accidents.

[0003] The demand for vehicle-mounted DMS systems has increased significantly in the market, and the technical requirements for DMS optical lens imaging systems have also become increasingly higher. The existing vehicle-mounted DMS lens imaging technology generally has problems such as large size, high cost, poor stability to high and low temperature thermal drift, and severe edge distortion of the captured scene. Utility Model Content

[0004] The utility model provides an ultra-thin DMS monitoring optical system and an imaging device. The ultra-thin DMS monitoring optical system and the imaging device have the characteristics of low cost, miniaturization, no heat and no distortion.

[0005] The above technical objectives of the utility model are achieved through the following technical solutions: an ultra-thin DMS monitoring optical system and imaging device, which includes: an aperture, a first lens, a second lens, a third lens, a fourth lens, a filter, a protective glass and an image plane in sequence along the optical axis from the object plane to the image plane;

[0006] The object side of the first lens is convex, and the image side is convex;

[0007] The object side of the second lens is convex, and the image side is concave;

[0008] The object side of the third lens is concave and the image side is convex;

[0009] The fourth lens has a small convex surface on the object side and a small concave surface on the image side;

[0010] And the following relationship is satisfied:

[0011] 0.8<f1 / f<1.7; 1.3<f2 / f<2.2; 0.3<f3 / f<0.8; 0.6<f4 / f<1.2;

[0012] Among them, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, and f is the effective focal length of the entire optical system.

[0013] In some embodiments, the refractive index Nd2 of the second lens, the refractive index Nd3 of the third lens, and the refractive index Nd4 of the fourth lens are all greater than 1.5 and less than 1.7, and the Abbe constant Vd1 of the first lens, the Abbe constant Vd2 of the second lens, and the Abbe constant Vd3 of the third lens are all greater than 36 and less than 60.

[0014] In some embodiments, the total optical length TTL of the optical system satisfies the following conditions:

[0015] 7.5mm≤TTL≤9mm.

[0016] In some embodiments, the optical system satisfies the following condition:

[0017] 0.9<L / h<1.4;

[0018] Where: L represents the total length of the optical lens, and h represents the size of the image plane.

[0019] In some embodiments, the first lens is a biconvex lens having positive optical power;

[0020] The second lens is a meniscus lens with negative optical power;

[0021] The third lens is a meniscus lens with positive optical power;

[0022] The fourth lens is an M-type lens, and its optical power is negative.

[0023] In some embodiments, the aperture stop is disposed before the first lens.

[0024] In summary, the utility model has the following beneficial effects:

[0025] Low cost and miniaturization: There are only 4 lenses, 3 plastic lenses and 1 glass lens, which makes the overall structure of the lens compact and small in size; at the same time, the design structure is simple, easy to assemble and mass produce, which can well control costs and achieve high cost performance.

[0026] Athermalization: In environments with large temperature changes, such as direct sunlight or cold weather, the optical system can still maintain stable imaging performance without image quality degradation due to temperature changes.

[0027] No distortion: By optimizing the optical design, the range of optical distortion at the edge of the field of view is strictly controlled, thereby reducing the deformation of the image edge, making objects at the edge easier to identify and track. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the lens of the utility model;

[0029] Figure 2 This is the MTF analysis diagram of the utility model under the infrared 940nm light condition;

[0030] Figure 3 This is the defocus curve diagram of the utility model at 20°C under the infrared 940nm light condition;

[0031] Figure 4 This is the defocus curve diagram of the utility model at -40°C under the infrared 940nm light condition;

[0032] Figure 5 This is the defocus curve of the utility model at 80°C under the condition of infrared 940nm light;

[0033] Figure 6 This is the field curvature diagram of the utility model under the infrared 940nm light condition;

[0034] Figure 7 This is the optical distortion diagram of the utility model under infrared 940nm light conditions.

[0035] In the figure: STO (Stop): aperture; E1: first lens; E2: second lens; E3: third lens; E4: fourth lens; IR (InfraredFilter): filter; CG (Coverglass): protective glass; IMA (ImageSurface): image surface;

[0036] S1: the side of the first lens facing the object side; S2: the side of the first lens facing the image side; S3: the side of the second lens facing the object side; S4: the side of the second lens facing the image side; S5: the side of the third lens facing the object side; S6: the side of the third lens facing the image side; S7: the side of the fourth lens facing the object side; S8: the side of the fourth lens facing the image side. DETAILED DESCRIPTION

[0037] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0038] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0039] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present utility model, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0040] In the present invention, unless otherwise clearly specified and limited, the terms "install", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] like Figure 1 As shown, this embodiment provides an ultra-thin DMS monitoring optical system and an imaging device, which includes: an aperture, a first lens, a second lens, a third lens, a fourth lens, a filter, a protective glass and an image plane in sequence along the optical axis from the object plane to the image plane;

[0042] The object side of the first lens is convex, and the image side is convex;

[0043] The object side of the second lens is convex, and the image side is concave;

[0044] The object side of the third lens is concave and the image side is convex;

[0045] The fourth lens has a small convex surface on the object side and a small concave surface on the image side;

[0046] And the following relationship is satisfied:

[0047] 0.8<f1 / f<1.7; 1.3<f2 / f<2.2; 0.3<f3 / f<0.8; 0.6<f4 / f<1.2;

[0048] Among them, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, and f is the effective focal length of the entire optical system.

[0049] Furthermore, the refractive index Nd2 of the second lens, the refractive index Nd3 of the third lens, and the refractive index Nd4 of the fourth lens are all greater than 1.5 and less than 1.7, and the Abbe constant Vd1 of the first lens, the Abbe constant Vd2 of the second lens, and the Abbe constant Vd3 of the third lens are all greater than 36 and less than 60.

[0050] Furthermore, the total optical length TTL of the optical system satisfies the following conditions:

[0051] 7.5mm≤TTL≤9mm.

[0052] Furthermore, the optical system satisfies the following conditional formula:

[0053] 0.9<L / h<1.4;

[0054] Where: L represents the total length of the optical lens, and h represents the size of the image plane.

[0055] Furthermore, the first lens is a biconvex lens, and its optical power is positive;

[0056] The second lens is a meniscus lens with negative optical power;

[0057] The third lens is a meniscus lens with positive optical power;

[0058] The fourth lens is an M-type lens, and its optical power is negative.

[0059] Furthermore, the aperture is arranged before the first lens.

[0060] In the embodiment of this patent, when the working distance is 0.8 meters, the total focal length of the lens is f=5.1mm, FNO=2.0, the total optical length TTL=8.65mm, the maximum image circle is 7mm, the lens diameter is 7.2mm, and the optical distortion is less than 5%.

[0061] The parameters of the lens group are listed in Table 1:

[0062]

[0063] Table 1

[0064] Aspheric coefficients are shown in Table 2:

[0065]

[0066]

[0067] Table 2

[0068] The aspheric coefficients satisfy the following equation:

[0069]

[0070] Among them, z is the aspheric surface sag, c is the aspheric surface paraxial curvature, y is the lens aperture, k is the cone coefficient, a4 is the 4th aspheric surface coefficient, a6 is the 6th aspheric surface coefficient, a8 is the 8th aspheric surface coefficient, a 10 is the 10th-order aspheric coefficient, a 12 is the 12th-order aspheric coefficient, a 14 is the 14th-order aspheric coefficient.

[0071] Specifically, the R value (Radius curvature radius), thickness (Thickness), refractive index (Index), Abbe coefficient (ABB), lens focal length (EFL-E) of each lens surface in this embodiment are shown in Table 1, and the aspheric surface parameters are shown in Table 2.

[0072] In the embodiment of the present utility model, Figure 2 The modulation transfer function (MTF) curve in the infrared light band represents the comprehensive resolution ability of the optical system. The horizontal axis of the figure represents the spatial frequency, the unit is cycles per millimeter (cycles / mm), and the vertical axis represents the value of the modulation transfer function (MTF). The value of MTF is used to evaluate the imaging quality of the lens, and the value range is 0-1. It is particularly pointed out that the optical transfer function is used to evaluate the imaging quality of an optical system. The higher and smoother the curve is, the better the imaging quality of the system is, and the stronger the ability to restore the real image is; from Figure 2 It can be seen that when the spatial frequency of the infrared light band is 83lp / mm, the MTF of the imaging area near the center is > 0.7, and the imaging quality is good. Figure 3 It is represented as the defocus curve at 20℃ in the infrared light band. Figure 3 It can be seen that the MTF concentration of this lens is good, which is convenient for focusing. Figure 4 and Figure 5 It can be seen that the defocus curves at low temperature of -40℃ and high temperature of 80℃ both meet high resolution, the focus change of the defocus curve is small, and the thermal drift effect is stable; Figure 6 Represented as a field curvature diagram, Figure 6 It can be seen that the field curvature value is controlled between -0.05mm and 0.05mm. The smaller the field curvature value, the better the imaging quality of the lens. Figure 7 Expressed as an optical distortion diagram, it can be concluded that the absolute value of the optical distortion is less than 5%. The smaller the optical distortion, the smaller the deformation of the edge of the imaging picture.

[0073] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. An ultra-thin DMS monitoring optical system, characterized in that: The optical axis includes, from the object plane to the image plane, an aperture, a first lens, a second lens, a third lens, a fourth lens, a filter, a protective glass and an image plane; The object side of the first lens is convex, and the image side is convex; The object side of the second lens is convex, and the image side is concave; The object side of the third lens is concave and the image side is convex; The fourth lens has a small convex surface on the object side and a small concave surface on the image side; And the following relationship is satisfied: 0.8<f1 / f<1.7; 1.3<f2 / f<2.2; 0.3<f3 / f<0.8; 0.6<f4 / f<1.2; Among them, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, and f is the effective focal length of the entire optical system.

2. The ultra-thin DMS monitoring optical system according to claim 1, characterized in that: The refractive index Nd2 of the second lens, the refractive index Nd3 of the third lens, and the refractive index Nd4 of the fourth lens are all greater than 1.5 and less than 1.7, and the Abbe constant Vd1 of the first lens, the Abbe constant Vd2 of the second lens, and the Abbe constant Vd3 of the third lens are all greater than 36 and less than 60.

3. The ultra-thin DMS monitoring optical system according to claim 1, characterized in that: The total optical length TTL of the optical system meets the following conditions: 7.5mm≤TTL≤9mm.

4. The ultra-thin DMS monitoring optical system according to claim 1, characterized in that: The optical system satisfies the following conditions: 0.9<L / h<1.4; Where: L represents the total length of the optical lens, and h represents the size of the image plane.

5. The ultra-thin DMS monitoring optical system according to claim 1, characterized in that: The first lens is a biconvex lens with positive optical power; The second lens is a meniscus lens with negative optical power; The third lens is a meniscus lens with positive optical power; The fourth lens is an M-type lens, and its optical power is negative.

6. The ultra-thin DMS monitoring optical system according to claim 1, characterized in that: The aperture is arranged before the first lens.

Images