Large-field-angle vehicle-mounted DMS monitoring lens and camera module

Abstract

The invention relates to the technical field of optical lenses, and discloses a large-field-angle vehicle-mounted DMS monitoring lens and a camera module, and the vehicle-mounted DMS monitoring lens comprises a first lens, a second lens, a third lens and a fourth lens which are sequentially arranged from an object side to an image side along an optical axis; the first lens has negative focal power, the object side surface of the first lens is of a convex surface structure, and the image side surface is of a concave surface structure; the second lens has negative focal power, the object side surface of the second lens is of a concave surface structure, and the image side surface is of a convex surface structure; the third lens has positive focal power, and the object side surface and the image side surface of the third lens are of convex surface structures; the fourth lens has positive focal power, and the object side surface and the image side surface of the fourth lens are of convex surface structures; wherein the first lens and the fourth lens are plastic aspheric lenses, and the second lens and the third lens are glass spherical lenses. Through the shape design and the material, the vehicle-mounted DMS monitoring lens has the characteristics of miniaturization, large field angle, ultra-wide field depth coverage, high image quality, low cost, low temperature drift, obvious imaging picture ghosting elimination effect and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of optical lenses, and in particular to a vehicle-mounted DMS monitoring lens with a large field of view and a camera module. Background Art

[0002] Fatigue driving is a leading cause of traffic accidents worldwide, especially in long-distance transport scenarios. Traditional external environmental monitoring systems cannot effectively address driver distraction and slow reaction times due to fatigue. Driver status monitoring systems, which capture real-time characteristics such as eye closure frequency, head posture, and gaze deviation, have become a core technology that fills this gap in in-vehicle safety monitoring.

[0003] However, existing DMS monitoring lenses generally have a field of view of less than 120°, failing to cover the driver's entire body and the cabin environment in large vehicles like SUVs and MPVs. Furthermore, limited in-vehicle installation space means existing DMS monitoring lenses are too long and bulky to be discreetly installed.

[0004] In addition, the lenses of existing DMS monitoring cameras are made of plastic or glass. When the temperature inside the car fluctuates greatly, it will cause thermal expansion of the plastic lens or stress cracking of the glass lens, further leading to focal length drift and stray light ghosting.

[0005] Finally, the existing DMS monitoring lens has a limited depth of field. When the driver adjusts the seat distance, frequent automatic focus is required, and the response time is too long, resulting in prolonged fatigue warning, which cannot meet real-time monitoring needs. Summary of the Invention

[0006] In order to solve the problems of small field of view, large size, and large temperature fluctuations in the vehicle caused by the DMS monitoring lens in the above-mentioned prior art, such as focal length drift and stray light ghosting, the present invention provides a vehicle-mounted DMS monitoring lens with a large field of view and a camera module.

[0007] The technical effects to be achieved by the present invention are achieved through the following technical aspects:

[0008] In a first aspect, the present invention provides a vehicle-mounted DMS monitoring lens with a large field of view, comprising: a first lens, a second lens, a third lens, and a fourth lens arranged in sequence from the object side to the image side along the optical axis;

[0009] The first lens has negative optical power, the object side surface of the first lens is convex, and the image side surface of the first lens is concave;

[0010] The second lens has negative optical power, the object side surface of the second lens is concave, and the image side surface of the second lens is convex;

[0011] The third lens has positive refractive power, and the object-side surface and the image-side surface of the third lens are convex structures;

[0012] The fourth lens has positive refractive power, and the object-side surface and the image-side surface of the fourth lens are convex structures;

[0013] Wherein, the first lens and the fourth lens are plastic aspherical lenses, and the second lens and the third lens are glass spherical lenses.

[0014] In some optional implementations, the effective focal lengths of the first lens, the second lens, the third lens, and the fourth lens satisfy the following conditional formula:

[0015] -2.0≤f1 / f≤-1.9;

[0016] -6.2≤f2 / f≤-5.9

[0017] 2.0≤f3 / f≤2.3

[0018] 2.2≤f4 / f≤2.5;

[0019] Among them, f1 is the effective focal length of the first lens, f2 is the effective focal length of the second lens, f3 is the effective focal length of the third lens, f4 is the effective focal length of the fourth lens, and f is the effective focal length of the vehicle-mounted DMS monitoring lens.

[0020] In some optional implementations, the refractive indices of the first lens, the second lens, the third lens, and the fourth lens satisfy the following conditional formula:

[0021] 1.61≤Nd1≤1.65;

[0022] 1.59≤Nd2≤1.63;

[0023] 1.88≤Nd3≤1.92;

[0024] 1.61≤Nd4≤1.65;

[0025] Wherein, Nd1 is the refractive index of the first lens, Nd2 is the refractive index of the second lens, Nd3 is the refractive index of the third lens, and Nd4 is the refractive index of the fourth lens.

[0026] In some optional implementations, the Abbe coefficients of the first lens, the second lens, the third lens, and the fourth lens satisfy the following conditional formula:

[0027] 21≤Vd1≤30;

[0028] 60≤Vd2≤65;

[0029] 32≤Vd3≤37;

[0030] 21≤Vd4≤30;

[0031] Wherein, Vd1 is the dispersion coefficient of the first lens, Vd2 is the dispersion coefficient of the second lens, Vd3 is the dispersion coefficient of the third lens, and Vd4 is the dispersion coefficient of the fourth lens.

[0032] In some optional implementations, the FOV, f, and h of the vehicle-mounted DMS monitoring camera satisfy the following conditional formula:

[0033] 53≤(FOV×f) / h≤57;

[0034] Among them, FOV is the maximum field of view angle of the vehicle-mounted DMS monitoring lens, h is the image height corresponding to the maximum field of view angle of the vehicle-mounted DMS monitoring lens, and f is the effective focal length of the vehicle-mounted DMS monitoring lens.

[0035] In some optional implementations, the BFL and f of the vehicle-mounted DMS monitoring camera satisfy the following conditional formula:

[0036] 1.5≤BFL / f≤1.8;

[0037] Among them, BFL is the axial distance from the center of the image-side surface of the fourth lens of the vehicle-mounted DMS monitoring lens to the imaging surface of the vehicle-mounted DMS monitoring lens, and f is the effective focal length of the vehicle-mounted DMS monitoring lens.

[0038] In some optional implementations, the BFL and TTL of the vehicle-mounted DMS monitoring camera meet the following conditional formula:

[0039] 0.25≤BFL / TTL≤0.3;

[0040] Among them, BFL is the axial distance from the center of the image side surface of the fourth lens of the vehicle-mounted DMS monitoring lens to the imaging surface of the vehicle-mounted DMS monitoring lens, and TTL is the axial distance from the center of the object side surface of the first lens of the vehicle-mounted DMS monitoring lens to the imaging surface of the vehicle-mounted DMS monitoring lens.

[0041] In some optional implementations, a stop S5 is provided between the second lens and the third lens;

[0042] The on-axis distance between the first lens and the second lens is set in the range of: 1.5mm to 1.7mm;

[0043] The on-axis distance between the second lens and the aperture S5 is set in the range of: 0.1mm to 0.15mm;

[0044] The on-axis distance between the aperture S5 and the third lens is set in the range of: -0.05mm to 0mm;

[0045] The on-axis distance between the third lens and the fourth lens is set in the range of 0.6 mm to 0.7 mm.

[0046] In some optional implementations, the aperture value of the vehicle-mounted DMS monitoring lens satisfies: FNO ≥ 2.0.

[0047] In a second aspect, the present invention provides a camera module, which includes a photosensitive chip and the vehicle-mounted DMS monitoring lens as described above, and the photosensitive chip is arranged on the image side of the vehicle-mounted DMS monitoring lens.

[0048] In summary, the present invention has at least the following benefits:

[0049] The present invention provides a vehicle-mounted DMS monitoring lens with a large field of view. The first lens has negative optical power and adopts a plastic aspheric lens, which is conducive to improving the field of view and can achieve a field of view greater than 142 degrees. It can also correct distortion aberrations to ensure that the driver's facial features are not significantly deformed. Combined with its shape design, the head size of the vehicle-mounted DMS monitoring lens can be reduced and the total optical length can be shortened; the second lens has negative optical power and adopts a glass spherical lens. Combined with its shape design, it can further collect light included by the first lens, achieve separation of positive and negative optical power, optimize astigmatism and field curvature, and ensure edge field clarity; the third lens has positive optical power and adopts a glass spherical lens. Combined with its shape design, it has a higher refractive index and can compensate for thermal expansion of the plastic aspheric lens to achieve low-temperature drift; the fourth lens has positive optical power and adopts a plastic aspheric lens. Combined with its shape design, it can further correct high-order aberrations of the vehicle-mounted DMS monitoring lens and control the CRA angle. The large-field-of-view vehicle-mounted DMS monitoring lens provided by the present invention can be concealedly installed on the steering wheel column through the above-mentioned shape design and material combination. It has the characteristics of miniaturization, large field of view, ultra-wide depth of field coverage, high image quality, low cost, low temperature drift, and obvious ghost image elimination effect in the imaging image. At the same time, it ensures high resolution across the entire field of view to clearly capture fatigue characteristics such as blinking and yawning, thereby realizing real-time monitoring of the driver's fatigue status. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A schematic structural diagram of a vehicle-mounted DMS monitoring lens with a large field of view provided by an embodiment of the present invention.

[0051] Figure 2 A schematic diagram of the through-focus MTF curve of a vehicle-mounted DMS monitoring lens with a large field of view over the entire operating band provided by an embodiment of the present invention.

[0052] Figure 3A schematic diagram of the MTF field of view relationship curve for the full working band of a large field of view vehicle-mounted DMS monitoring lens provided by an embodiment of the present invention.

[0053] Figure 4 A schematic diagram of field curvature and distortion across the full operating band of a vehicle-mounted DMS monitoring lens with a large field of view provided by an embodiment of the present invention.

[0054] Figure 5 A schematic diagram of a relative illumination curve of the central band of a vehicle-mounted DMS monitoring lens with a large field of view provided by an embodiment of the present invention.

[0055] Markings in the figure:

[0056] L1, first lens;

[0057] L2, second lens;

[0058] L3, third lens;

[0059] L4, fourth lens;

[0060] L5, filter. DETAILED DESCRIPTION

[0061] To make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0062] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0063] Example 1

[0064] In order to solve the problems of DMS monitoring lenses in the prior art, such as small field of view, large size, and large temperature fluctuations in the vehicle, which may cause focus drift and stray light ghosting, the embodiments of the present invention provide a vehicle-mounted DMS monitoring lens with a large field of view.

[0065] See also Figure 1 The embodiment of the present invention provides a vehicle-mounted DMS monitoring lens with a large field of view, including: a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4, which are arranged in sequence from the object side to the image side along the optical axis.

[0066] The shapes of the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 are designed as follows:

[0067] The first lens L1 has negative refractive power. The object-side surface S1 of the first lens L1 has a convex structure, and the image-side surface S2 of the first lens L1 has a concave structure.

[0068] The second lens L2 has negative refractive power, the object-side surface S3 of the second lens L2 has a concave structure, and the image-side surface S4 of the second lens L2 has a convex structure.

[0069] The third lens L3 has positive refractive power, and the object-side surface S6 and the image-side surface S7 of the third lens L3 are convex structures.

[0070] The fourth lens L4 has positive refractive power, and the object-side surface S8 and the image-side surface S9 of the fourth lens L4 are convex structures.

[0071] The first lens L1 and the fourth lens L4 are plastic aspherical lenses, and the second lens L2 and the third lens L3 are glass spherical lenses.

[0072] In this embodiment, the design of the first lens L1 can also be understood as follows: the first lens L1 is a meniscus negative concave lens, whose object-side surface S1 is convex, and whose image-side surface S2 is concave, and has negative optical power.

[0073] The design of the second lens L2 can also be understood as follows: the second lens L2 is a meniscus convex negative lens, whose object-side surface S3 is concave, the image-side surface S4 is convex, and has negative optical power.

[0074] The design of the third lens L3 can also be understood as follows: the third lens L3 is a biconvex positive lens, whose object-side surface S6 and image-side surface S7 are both convex structures and have positive refractive power.

[0075] The design of the fourth lens L4 can also be understood as follows: the fourth lens L4 is a biconvex positive lens, whose object-side surface S8 and image-side surface S9 are both convex structures and have positive refractive power.

[0076] During imaging, light enters the first lens L1, the second lens L2, the third lens L3 and the fourth lens L4 in sequence from the object side surface S1 of the first lens L1, and is finally imaged on the imaging surface of the vehicle-mounted DMS monitoring lens.

[0077] This embodiment provides a vehicle-mounted DMS monitoring lens with a large field of view. The first lens element L1 has negative optical power and is a plastic aspheric lens. This improves the field of view, achieving a field of view greater than 142°, and corrects distortion to ensure that the driver's facial features are not significantly deformed. Its shape design reduces the head size of the vehicle-mounted DMS monitoring lens and shortens the overall optical length. The second lens element L2 has negative optical power and is a glass spherical lens. Its shape design further collects light rays received by the first lens L1, separates positive and negative optical powers, optimizes astigmatism and field curvature, and ensures edge field clarity. The third lens element L3 has positive optical power and is a glass spherical lens. Its shape design provides a high refractive index, which can compensate for thermal expansion of the plastic aspheric lens and achieve low-temperature drift. The fourth lens element L4 has positive optical power and is a plastic aspheric lens. Its shape design further corrects high-order aberrations of the vehicle-mounted DMS monitoring lens and controls the CRA angle. Therefore, the large field-of-view vehicle-mounted DMS monitoring lens provided in this embodiment can be concealedly installed on the steering wheel column through the above-mentioned shape design and material combination. It has the characteristics of miniaturization, large field of view, ultra-wide depth of field coverage, high image quality, low cost, low temperature drift, and obvious ghost image elimination effect in the imaging image. At the same time, it ensures high resolution across the entire field of view to clearly capture fatigue characteristics such as blinking and yawning, thereby realizing real-time monitoring of the driver's fatigue status.

[0078] Furthermore, the second and third lenses L2 and L3 of this embodiment's wide-field-of-view automotive DMS surveillance lens utilize glass spherical lenses with low thermal expansion coefficients and high Abbe numbers to compensate for the temperature sensitivity of the plastic aspherical first and fourth lenses L1 and L4. This ensures that the focal length drift of this embodiment's wide-field-of-view automotive DMS surveillance lens is less than ±0.04mm within the -40°C to 85°C temperature range, an 80% improvement compared to an all-plastic lens.

[0079] This embodiment, as a preferred embodiment, further optimizes the structure of the vehicle-mounted DMS monitoring lens. Specifically, an aperture S5 is provided between the second lens L2 and the third lens L3, and the aperture effect is optimized by adjusting the diameter of the aperture S5.

[0080] Based on the structural design of the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4, and in conjunction with the aperture S5, the on-axis distances between the lenses are optimized so that the on-axis distances between two adjacent lenses satisfy the following relationship:

[0081] The on-axis distance between the first lens L1 and the second lens L2 is set in the range of: 1.5mm to 1.7mm;

[0082] The on-axis distance between the second lens L2 and the aperture S5 is set in the range of 0.1 mm to 0.15 mm.

[0083] The on-axis distance between the aperture S5 and the third lens L3 is set in the range of: -0.05mm to 0mm;

[0084] The on-axis distance between the third lens L3 and the fourth lens L4 is set in the range of: 0.6 mm to 0.7 mm.

[0085] As a preferred embodiment, this embodiment further includes a filter L5, which is arranged on the image side of the fourth lens L4 and is used to filter infrared light and improve image contrast.

[0086] In this embodiment, through the shape design of the first lens L1, the second lens L2, the third lens L3 and the fourth lens L4, combined with the design of the on-axis distance between adjacent lenses, the total optical length of the vehicle-mounted DMS monitoring lens of this embodiment is reduced to 10.3 mm, and the optical head size is 5 mm, which meets the requirements for installation in the narrow space inside the vehicle. BFL / f=1.623 (BFL=2.816 mm), while also reserving space for the filter L5 and sensor.

[0087] In this embodiment, which is a preferred embodiment, the effective focal lengths of the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 of the vehicle-mounted DMS monitoring lens are designed to satisfy the following conditional formula:

[0088] -2.0≤f1 / f≤-1.9;

[0089] -6.2≤f2 / f≤-5.9

[0090] 2.0≤f3 / f≤2.3

[0091] 2.2≤f4 / f≤2.5;

[0092] Among them, f1 is the effective focal length of the first lens L1, f2 is the effective focal length of the second lens L2, f3 is the effective focal length of the third lens L3, f4 is the effective focal length of the fourth lens L4, and f is the effective focal length of the vehicle-mounted DMS monitoring lens.

[0093] In this embodiment, the effective focal length of the first lens L1 satisfies -2.0≤f1 / f≤-1.9, so that the negative optical power of the first lens L1 accounts for approximately 46%, and the effective focal length of the third lens L3 satisfies 2.0≤f3 / f≤2.3, so that the positive optical power of the third lens L3 accounts for approximately 52%, thereby ensuring that the total focal length f=1.735mm of the vehicle-mounted DMS monitoring lens, achieving a short focus and a large field of view.

[0094] In this embodiment, which is a preferred embodiment, the refractive indices of the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 of the vehicle-mounted DMS monitoring lens are designed to satisfy the following conditional formula:

[0095] 1.61≤Nd1≤1.65;

[0096] 1.59≤Nd2≤1.63;

[0097] 1.88≤Nd3≤1.92;

[0098] 1.61≤Nd4≤1.65;

[0099] Wherein, Nd1 is the refractive index of the first lens L1, Nd2 is the refractive index of the second lens L2, Nd3 is the refractive index of the third lens L3, and Nd4 is the refractive index of the fourth lens L4.

[0100] In this embodiment, the first lens L1 is made of a material with a higher refractive index to enhance the light divergence ability. Combined with the shape design, the field of view angle of the vehicle-mounted DMS monitoring lens reaches 142°, and the incident angle of the edge light is increased to 65° while still maintaining effective control. The thickness of the first lens L1 is shortened to 0.55mm, and the size of the optical head is compressed to 5mm.

[0101] The second lens L2 is made of a material with a higher refractive index to reduce interface reflection, and its shape is designed to correct the spherical aberration and coma introduced by the first lens L1.

[0102] The third lens element, L3, utilizes an ultra-high refractive index material, increasing its radius of curvature to 6.4mm and reducing its thickness to just 1.3mm. This provides 52% of the positive focal power of the automotive DMS monitoring lens while shortening the overall optical length to 10.3mm. The high-refractive-index material's thermo-optical coefficient compensates for that of the plastic fourth lens element, L4, ensuring a focal length drift of less than ±0.04mm between -40°C and 85°C.

[0103] The fourth lens element L4 is made of a higher refractive index material, and has a refractive index difference of Δn = 0.27 with the third lens element L3. Combined with its shape design, it corrects the field curvature and distortion remaining in the third lens element L3, controls the chief ray angle CRA to < 30°, and the relative illumination of the edge field of view to > 50%, thereby preventing "dark corners" from affecting driver facial detection.

[0104] In this embodiment, which is a preferred embodiment, the chromatic aberration coefficients of the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 of the vehicle-mounted DMS monitoring lens are designed to satisfy the following conditional formula:

[0105] 21≤Vd1≤30;

[0106] 60≤Vd2≤65;

[0107] 32≤Vd3≤37;

[0108] 21≤Vd4≤30;

[0109] Wherein, Vd1 is the chromatic aberration coefficient of the first lens L1, Vd2 is the chromatic aberration coefficient of the second lens L2, Vd3 is the chromatic aberration coefficient of the third lens L3, and Vd4 is the chromatic aberration coefficient of the fourth lens L4.

[0110] In this embodiment, by designing the dispersion coefficients of the first lens L1 and the third lens L3, and based on the principle that the Abbe numbers of positive and negative optical power lenses complement each other and offset the focal length differences of light of different wavelengths, the axial chromatic aberration of the vehicle-mounted DMS monitoring lens of this embodiment is reduced to less than ±0.03 mm.

[0111] At the same time, based on the principle that the incident angle of light at the edge of a large field of view lens is high and light of different wavelengths produces lateral displacement, the dispersion coefficient design of the second lens L2 and the fourth lens L4, combined with their shape design, make the main light rays of different colors converge at the same point, thereby making the lateral chromatic aberration of the on-board DMS monitoring lens <±2μm, the color reproduction of the edge field of view is improved, and the overlap of the three RGB channels of the facial contour >98%.

[0112] The third lens L3 uses a high refractive index and medium dispersion to compensate for the high thermo-optical coefficient of the plastic of the first lens L1 and the fourth lens L4, thereby reducing thermal expansion and fine-tuning the dispersion characteristics. As a result, the chromatic aberration of the vehicle-mounted DMS monitoring lens changes within the temperature range of -40℃ to 85℃, less than ±0.01mm.

[0113] In this embodiment, which is a preferred embodiment, the FOV of the vehicle-mounted DMS monitoring camera is designed so that FOV, f, and h satisfy the following conditional formula:

[0114] 53≤(FOV×f) / h≤57;

[0115] Among them, FOV is the maximum field of view angle of the vehicle-mounted DMS monitoring lens, h is the image height corresponding to the maximum field of view angle of the vehicle-mounted DMS monitoring lens, and f is the effective focal length of the vehicle-mounted DMS monitoring lens.

[0116] This embodiment is a preferred embodiment. The BFL of the vehicle-mounted DMS monitoring camera is designed so that the BFL and f satisfy the following conditional formula:

[0117] 1.5≤BFL / f≤1.8;

[0118] Among them, BFL is the axial distance from the center of the image-side surface of the fourth lens L4 of the vehicle-mounted DMS monitoring lens to the imaging surface of the vehicle-mounted DMS monitoring lens, and f is the effective focal length of the vehicle-mounted DMS monitoring lens.

[0119] In this embodiment, based on the parameter design of f, BFL=2.816 mm, and a 0.3 mm thick filter L5 can be installed to improve the low-light imaging quality and make the noise less than 5%.

[0120] This embodiment is a preferred embodiment, and the TTL of the vehicle-mounted DMS monitoring camera is designed so that the BFL and TTL satisfy the following conditional formula:

[0121] 0.25≤BFL / TTL≤0.3;

[0122] Among them, BFL is the axial distance from the center of the image side surface of the fourth lens L4 of the vehicle-mounted DMS monitoring lens to the imaging surface of the vehicle-mounted DMS monitoring lens, and TTL is the axial distance from the center of the object side surface of the first lens L1 of the vehicle-mounted DMS monitoring lens to the imaging surface of the vehicle-mounted DMS monitoring lens.

[0123] In this embodiment, which is a preferred embodiment, the aperture value of the vehicle-mounted DMS monitoring lens is designed so that the aperture value of the vehicle-mounted DMS monitoring lens satisfies: FNO ≥ 2.0.

[0124] An embodiment of the present invention provides a vehicle-mounted DMS monitoring lens with a large field of view. Through the above-mentioned shape design and parameter design, it achieves a field of view greater than 142° and an aperture FNO of 2.0. Combined with the effective focal length f = 1.735mm of the vehicle-mounted DMS monitoring lens, the depth of field range reaches 0.3m~∞, thereby enabling the vehicle-mounted DMS monitoring lens to clearly image the driver's near and far fields without the need for automatic focus.

[0125] In this embodiment, which is a preferred embodiment, the first lens L1, the second lens L2, the aperture S5, the third lens L3, the fourth lens L4, and the filter L5 of the vehicle-mounted DMS monitoring lens are designed to achieve the above-mentioned shape and related parameters. The specific parameters used are as follows:

[0126] Table 1: Shape design parameters of the vehicle-mounted DMS monitoring lens protected by this embodiment:

[0127]

[0128]

[0129] In Table 1 above, the surface numbers are numbered according to the order of the surfaces of each lens, where "S1" represents the object-side surface of the first lens L1, "S2" represents the image-side surface of the first lens L1, "S3" represents the object-side surface of the second lens L2, "S4" represents the image-side surface of the second lens L2, "S5" represents the aperture S5, "S6" represents the object-side surface of the third lens L3, "S7" represents the image-side surface of the third lens L3, "S8" represents the object-side surface of the fourth lens L4, "S9" represents the image-side surface of the fourth lens L4, "S10" represents the object-side surface of the filter L5, and "S11" represents the image-side surface of the filter L5. On the image-side surface of the light sheet L5, "S12" and "S13" represent another filter; the radius of curvature represents the degree of curvature of the lens surface, a positive value represents that the surface is bent toward the image side, and a negative value represents that the surface is bent toward the object side; the thickness represents the central axial distance from the current surface to the next surface, the refractive index represents the ability of the material between the current surface and the next surface to deflect light, and a blank space represents that the current position is air, with a refractive index of 1; the Abbe number represents the dispersion characteristics of the material between the current surface and the next surface to light, and a blank space represents that the current position is air; the k value represents the numerical value of the best-fit cone coefficient of the aspheric surface.

[0130] The aspheric cone coefficient can be defined by the following aspheric formula, but is not limited to the following expression method:

[0131]

[0132] Among them, z is the axial sagittal height of the aspheric surface in the Z direction; r is the height of the aspheric surface; c is the curvature of the fitted sphere, which is the inverse of the curvature radius; k is the fitting cone coefficient; AG is the coefficient of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspheric polynomial.

[0133] In the embodiment, the shape of the first lens L1 is designed to provide negative optical power, diverge incident light to widen the field of view to 142°, and the aspherical design corrects barrel distortion.

[0134] By designing the shape of the second lens L2, the light diverged by the first lens L1 is converged, and the astigmatism (<±0.02mm) and field curvature (<±0.05mm) introduced at large angles are corrected.

[0135] By designing the shape of the third lens L3 to provide mainly positive focal power, the high refractive index compensates for the thermo-optical coefficient of the plastic lens and controls the thermal focal shift, so that the refractive index reaches n=1.91 and the thermal focal shift satisfies Δf<±0.04mm.

[0136] The shape of the fourth lens L4 is designed to correct high-order aberrations, control the chief ray angle so that the chief ray angle satisfies CRA<30°, and optimize the peripheral field illumination.

[0137] By disposing a stop S5 between the second lens element L2 and the third lens element L3 and designing the thickness of the stop S5, the incident angle of marginal light is limited to ≤60°.

[0138] By setting a filter L5 on the image side of the fourth lens L4 and matching its shape design, it can filter visible light and far infrared to improve image contrast.

[0139] Table 2: Aspheric lens design parameters of the first lens L1 and the fourth lens L4 of the vehicle-mounted DMS monitoring lens protected by this embodiment:

[0140]

[0141] Table 3: Other optical information design of the vehicle-mounted DMS monitoring lens protected by this embodiment:

[0142]

[0143]

[0144] D in Table 4 is the optically effective full aperture of the first lens L1.

[0145] In this embodiment, based on the shape design of the vehicle-mounted DMS monitoring lens, combined with the above parameter design, Figure 2 As shown in the schematic diagram of the defocus MTF curve of the full working band of the large field of view vehicle-mounted DMS monitoring lens, Figure 2 In the figure, the MTF value can represent the comprehensive imaging quality of the vehicle-mounted DMS monitoring lens with a large field of view. The higher the MTF value, the clearer the image. The defocus MTF curve is based on the current image plane and shows the change in MTF after moving back and forth along the optical axis. The horizontal coordinate represents the movement direction of the current image plane and the defocus amount (unit / mm), and the vertical coordinate represents the normalized MTF (no unit). T represents the meridian, S represents the arc loss, and each curve represents a different field of view angle. Figure 2 It can be seen that the defocus curve of the large field-of-view vehicle-mounted DMS monitoring lens provided in this embodiment is relatively concentrated, the MTF peak is high and the focal depth is obvious. The MTF peak within the focal depth of ±0.03mm is greater than 0.6, which adapts to the slight deviation of the image plane caused by vehicle bumps.

[0146] Combine Figure 3 As shown in the MTF field of view relationship curve diagram of a large field of view vehicle-mounted DMS monitoring lens in the full working band, Figure 3 As shown, this curve diagram can be used to macroscopically evaluate the MTF performance of each field of view. Figure 3 In the figure, the horizontal coordinate represents the field of view angle (unit / °), and the vertical coordinate represents the normalized MTF; Figure 3It can be seen that the large field of view vehicle-mounted DMS monitoring lens provided in this embodiment has a smooth transition between the T-line MTF and S-line MTF from the center to the edge of the field of view, and the difference between the two is small. The lens astigmatism is effectively controlled, and excellent imaging quality is achieved across the entire field of view. The edge field of view MTF of this vehicle-mounted DMS monitoring lens is 0.45, resulting in a full field of view resolution difference of less than 30%, meeting the driver's eye detail detection requirements.

[0147] Combine Figure 4 As shown in the diagram of field curvature and distortion of the full working band of the large field of view vehicle-mounted DMS monitoring lens, Figure 4 In the field curve, the horizontal coordinate represents the magnitude of the field curvature of the lens (unit / mm), and the vertical coordinate represents the normalized field of view; in the distortion curve, the horizontal coordinate represents the magnitude of the F-tan (theta) distortion (unit / %), and the vertical coordinate represents the normalized field of view. Figure 4 As can be seen, the field curvature of this wide-field-angle automotive DMS surveillance lens across different wavelengths is within ±0.05mm, demonstrating that the lens effectively controls field curvature. Furthermore, the F-tan (theta) distortion curves for each wavelength overlap and are smooth, demonstrating that the lens effectively controls distortion, with F-tan theta distortion less than 55%, thus avoiding misdetection caused by facial feature deformation.

[0148] Combine Figure 5 As shown in the relative illumination curve diagram of the central band of a large field of view vehicle-mounted DMS monitoring lens, Figure 5 In the , relative illumination is defined as the illumination intensity per unit area of ​​the image plane, which can be normalized to the illumination at the point with the maximum illumination in the field of view; the horizontal coordinate system represents the half field of view angle of the lens (unit / °), and the vertical coordinate system represents the relative illumination value of the monitoring lens (unit / %). The higher the relative illumination, the smaller the brightness difference in each direction of the final image, and the less local shadows will appear. Figure 5 It can be seen that the relative illumination of the large-viewing-angle vehicle-mounted DMS monitoring lens transitions smoothly from the center to the edge of the field of view, and the relative illumination at the edge of the field of view is still greater than 50%.

[0149] In some optional embodiments, the present invention further provides a camera module, which includes a photosensitive chip and the vehicle-mounted DMS monitoring lens described in any of the above embodiments, and the photosensitive chip is arranged on the image side of the vehicle-mounted DMS monitoring lens.

[0150] Specifically, the photosensitive surface of the photosensitive chip is located on the imaging surface of the vehicle-mounted DMS monitoring lens, and the light passing through the lens and incident on the photosensitive surface can be converted into an electrical signal of the image.

[0151] The camera module of this embodiment possesses all the technical benefits of the aforementioned in-vehicle DMS monitoring lens, namely, it can be concealedly mounted on the steering column. It features miniaturization, a wide field of view, ultra-wide depth of field coverage, high image quality, low cost, low temperature drift, and significant ghosting reduction. It also maintains high resolution across the entire field of view, enabling clear capture of fatigue signs such as blinking and yawning, enabling real-time monitoring of driver fatigue. Since these technical benefits have been detailed in the embodiment of the in-vehicle DMS monitoring lens, they will not be repeated here.

[0152] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0153] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" and the like indicate positions or locations based on the positions shown in the accompanying drawings, or the positions or locations in which the inventive product is typically placed when in use. These terms are intended solely to facilitate the description of the present invention and to simplify the description, and are not intended to indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third," etc., are used solely to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0154] Furthermore, terms such as "horizontal," "vertical," and "overhanging" do not necessarily imply that a component must be absolutely horizontal or overhanging, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but rather that it can be slightly tilted.

[0155] Although the present invention has been described with reference to the above specific embodiments, it will be apparent to those skilled in the art that many substitutions, modifications, and variations can be made based on the above. Therefore, all such substitutions, modifications, and variations are intended to be encompassed within the spirit and scope of the appended claims.

Claims

1. A vehicle-mounted DMS monitoring lens with a large field of view, characterized in that: include: a first lens, a second lens, a third lens, and a fourth lens arranged in sequence from the object side to the image side along the optical axis; The first lens has negative optical power, the object side surface of the first lens is convex, and the image side surface of the first lens is concave; The second lens has negative optical power, the object side surface of the second lens is concave, and the image side surface of the second lens is convex; The third lens has positive refractive power, and the object-side surface and the image-side surface of the third lens are convex structures; The fourth lens has positive refractive power, and the object-side surface and the image-side surface of the fourth lens are convex structures; Wherein, the first lens and the fourth lens are plastic aspherical lenses, and the second lens and the third lens are glass spherical lenses.

2. The vehicle-mounted DMS monitoring lens with a large field of view according to claim 1, characterized in that: The effective focal lengths of the first lens, the second lens, the third lens, and the fourth lens satisfy the following conditional formula: -2.0≤f1 / f≤-1.9; -6.2≤f2 / f≤-5.9 2.0≤f3 / f≤2.3 2.2≤f4 / f≤2.5; Among them, f1 is the effective focal length of the first lens, f2 is the effective focal length of the second lens, f3 is the effective focal length of the third lens, f4 is the effective focal length of the fourth lens, and f is the effective focal length of the vehicle-mounted DMS monitoring lens.

3. The vehicle-mounted DMS monitoring lens with a large field of view according to claim 1, characterized in that: The refractive indices of the first lens, the second lens, the third lens, and the fourth lens satisfy the following conditional formula: 1.61≤Nd1≤1.65; 1.59≤Nd2≤1.63; 1.88≤Nd3≤1.92; 1.61≤Nd4≤1.65; Wherein, Nd1 is the refractive index of the first lens, Nd2 is the refractive index of the second lens, Nd3 is the refractive index of the third lens, and Nd4 is the refractive index of the fourth lens.

4. The vehicle-mounted DMS monitoring lens with a large field of view according to claim 1, characterized in that: The Abbe coefficients of the first lens, the second lens, the third lens, and the fourth lens satisfy the following conditional formula: 21≤Vd1≤30; 60≤Vd2≤65; 32≤Vd3≤37; 21≤Vd4≤30; Wherein, Vd1 is the dispersion coefficient of the first lens, Vd2 is the dispersion coefficient of the second lens, Vd3 is the dispersion coefficient of the third lens, and Vd4 is the dispersion coefficient of the fourth lens.

5. The vehicle-mounted DMS monitoring lens with a large field of view according to claim 1, characterized in that: The FOV, f, and h of the vehicle-mounted DMS monitoring lens meet the following conditional formulas: 53≤(FOV×f) / h≤57; Among them, FOV is the maximum field of view angle of the vehicle-mounted DMS monitoring lens, h is the image height corresponding to the maximum field of view angle of the vehicle-mounted DMS monitoring lens, and f is the effective focal length of the vehicle-mounted DMS monitoring lens.

6. The vehicle-mounted DMS monitoring lens with a large field of view according to claim 1, characterized in that: The BFL and f of the vehicle-mounted DMS monitoring camera satisfy the following conditional formula: 1.5≤BFL / f≤1.8; Among them, BFL is the axial distance from the center of the image-side surface of the fourth lens of the vehicle-mounted DMS monitoring lens to the imaging surface of the vehicle-mounted DMS monitoring lens, and f is the effective focal length of the vehicle-mounted DMS monitoring lens.

7. The vehicle-mounted DMS monitoring lens with a large field of view according to claim 1, characterized in that: The BFL and TTL of the vehicle-mounted DMS monitoring camera meet the following conditions: 0.25≤BFL / TTL≤0.3; Among them, BFL is the axial distance from the center of the image side surface of the fourth lens of the vehicle-mounted DMS monitoring lens to the imaging surface of the vehicle-mounted DMS monitoring lens, and TTL is the axial distance from the center of the object side surface of the first lens of the vehicle-mounted DMS monitoring lens to the imaging surface of the vehicle-mounted DMS monitoring lens.

8. The vehicle-mounted DMS monitoring lens with a large field of view according to claim 1, characterized in that: A stop S5 is provided between the second lens and the third lens; The on-axis distance between the first lens and the second lens is set in the range of: 1.5 mm to 1.7 mm; The on-axis distance between the second lens and the aperture S5 is set in the range of: 0.1mm~0.15mm; The on-axis distance between the aperture S5 and the third lens is set in the range of: -0.05mm~0mm; The on-axis distance between the third lens and the fourth lens is set in the range of: 0.6mm~0.7mm.

9. The vehicle-mounted DMS monitoring lens with a large field of view according to claim 1, characterized in that: The aperture value of the vehicle-mounted DMS monitoring lens meets the following requirements: FNO ≥ 2.

0.

10. A camera module, characterized in that: The camera module includes a photosensitive chip and the vehicle-mounted DMS monitoring lens according to any one of claims 1 to 9, and the photosensitive chip is arranged on the image side of the vehicle-mounted DMS monitoring lens.

Images