Three-piece type small DMS lens and imaging method thereof

Abstract

The invention relates to a three-piece type small DMS lens and an imaging method thereof, an optical system of the lens is composed of a first lens, a second lens and a third lens which are sequentially arranged from left to right along a light incident light path, and a diaphragm is arranged in front of the first lens. Wherein the first lens is a glass aspheric lens, and the second lens and the third lens are plastic aspheric lenses. By reasonably distributing the focal power and the surface type of each lens, the central thickness of each lens, the axial distance between the lenses and the like, the lens has high resolution, low distortion, low temperature drift and good imaging quality, the total length of the lens is smaller than 7mm, the miniaturization design requirement is met, and meanwhile, the manufacturing cost of the lens is lower.

Description

Technical Field

[0001] This invention relates to the field of optical imaging technology, and in particular to a three-element miniature DMS lens and its imaging method. Background Technology

[0002] With the rapid development of the automotive industry and intelligent driving technology, driving safety has become a focus of social concern. Driver monitoring systems (DMS), as a core component for improving driving safety, effectively warn of dangerous driving situations by monitoring the driver's facial features and eye status (such as gaze direction and eye closure) in real time, thereby reducing the probability of accidents.

[0003] The performance of a DMS (Digital Mobile Assistant) is highly dependent on the quality of the images acquired by its front end. As the "eyes" of the DMS, the DMS lens needs to meet the stringent requirements of stable and clear imaging in complex automotive environments. However, existing ordinary lenses have a series of inherent technical defects when applied to DMS, mainly in the following aspects: 1. The contradiction between imaging quality and recognition accuracy: The DMS algorithm requires high-precision recognition of minute features such as the driver's eyelids and pupils. Existing lenses often suffer from insufficient resolution and severe image quality degradation at the edges of the field of view. 2. Insufficient temperature stability and reliability: The vehicle environment has a wide temperature range (-40℃ to 105℃). Glass lenses defocus due to temperature drift of the refractive index, affecting the imaging stability at high and low temperatures. Although all-plastic aspherical lenses are low-cost and easy to miniaturize, they have a high coefficient of thermal expansion and are prone to deformation at high temperatures, which exacerbates astigmatism and field curvature. 3. Difficulty in balancing miniaturization and high performance: For aesthetic and installation convenience, DMS lenses need to be miniaturized and lightweight. However, traditional lenses often use more lenses in pursuit of high image quality, resulting in large lens size and high cost. Summary of the Invention

[0004] In view of the shortcomings of existing technical solutions, the purpose of this invention is to provide a three-element miniature DMS lens and its imaging method. This three-element miniature DMS lens not only meets the product requirements of miniaturization and lightweighting, but also has optical performance such as high resolution, good temperature stability and low distortion.

[0005] This invention discloses a three-element miniature DMS lens, characterized in that: the lens comprises, sequentially from the object side to the image side along the optical axis, a first lens, a second lens, and a third lens; the first lens is a meniscus lens with positive optical power, its object side being concave and its image side being convex; the second lens is a meniscus lens with positive optical power, its object side being concave and its image side being convex; the third lens is a meniscus lens with negative optical power, its object side being convex and its image side being concave; the three lenses are made of glass or plastic material, wherein the first lens is a glass aspherical lens, and the second and third lenses are plastic aspherical lenses.

[0006] Furthermore, the focal length of the optical system of the lens is f, and the focal lengths of the first lens, the second lens, and the third lens are f1, f2, and f3, respectively, wherein f1, f2, f3, and f satisfy the following ratio: 1.0 <f1 / f<2.0,0.5<f2 / f<1.0,-1.0<f3 / f<-0.5。

[0007] Furthermore, the first lens satisfies the relationship: 2.0 ≤ N d ≤2.1, V d ≤50.0; The second lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≥50.0; The third lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≤50.0; where N d V is the refractive index. d Let be Abbe's constant.

[0008] Furthermore, the on-axis distances of the optical system satisfy the following relationship: the air gap between the first lens and the second lens is 0.5~1.0mm; the air gap between the second lens and the third lens is 0~0.5mm.

[0009] Furthermore, the first lens, the second lens, and the third lens are plastic aspherical lenses. The equation for the aspherical curve is:

[0010] Where Z is the distance from the vertex of the aspherical surface to the optical axis at a height of r; c is the paraxial curvature of the aspherical surface; k is the conic constant; α1, α2, α3, α4, α5, α6, α7, α8, α9, α 10 All are coefficients of higher-order terms.

[0011] Furthermore, the total optical length TTL of the optical system and the focal length f of the optical system satisfy the following condition: 2.0 ≤ TTL / f ≤ 2.5.

[0012] Furthermore, the F-number of the optical system is ≤2.0.

[0013] Furthermore, the image height H of the optical system and the focal length f of the optical system satisfy the following condition: H / f≥1.5.

[0014] Furthermore, the aperture stop of the optical system is located in front of the first lens.

[0015] Furthermore, a filter is provided on the rear side of the third lens.

[0016] Compared with the prior art, the present invention has the following advantages: This DMS lens employs a glass-plastic hybrid optical system, consisting of only one glass aspherical lens and two plastic aspherical lenses. By rationally allocating the optical power of each lens and adjusting their surface shape and on-axis distance, the lens achieves high resolution, low distortion, and low temperature drift, enabling clear imaging from -40℃ to 105℃. The overall lens length is significantly reduced to less than 7mm, meeting market demands for miniaturization and lightweight products. Compared to similar lenses, it has a wider field of view and a broader monitoring range. Furthermore, the optical system uses only three lenses, effectively reducing lens costs.

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the optical structure of the present invention; Figure 2 This is the axial chromatic aberration diagram of the entire working band of the present invention; Figure 3 This is the transverse chromatic aberration diagram of the entire working band of the present invention; Figure 4 This is the field curvature distortion diagram of the entire working band of the present invention; Figure 5 This is the MTF curve diagram of the entire operating band of this invention; In the diagram: STO - aperture stop; L1 - first lens; L2 - second lens; L3 - third lens; L4 - equivalent glass plate; IMA - imaging plane. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and specific implementation methods.

[0020] like Figure 1 As shown, a three-element miniature DMS lens is provided, comprising a first lens L1, a second lens L2, and a third lens L3 arranged sequentially from the object side to the image side. An aperture stop is positioned in front of the first lens. The first lens is a glass aspherical lens, while the second and third lenses are plastic aspherical lenses. The first lens is a meniscus lens with positive optical power, its object side being concave and its image side convex. The second lens is a meniscus lens with positive optical power, its object side being concave and its image side convex. The third lens is a meniscus lens with negative optical power, its object side being convex and its image side concave. Through the reasonable combination of the three lenses and the use of plastic aspherical lenses, the optical system possesses good aberration correction and resolving capabilities. Figures 2 to 5 As shown.

[0021] The optical system of the lens has a focal length of f, and the focal lengths of the first lens, second lens, and third lens are f1, f2, and f3, respectively. The ratio of f1, f2, and f3 to f satisfies the following condition: 1.0 <f1 / f<2.0,0.5<f2 / f<1.0,-1.0<f3 / f<-0.5。

[0022] The first lens satisfies the relationship: 2.0 ≤ N d ≤2.1, V d ≤50.0; The second lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≥50.0; The third lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≤50.0; where N d V is the refractive index. d Let be Abbe's constant.

[0023] The on-axis distances of the lens's optical system satisfy the following relationship: the air gap between the first lens and the second lens is 0.5~1.0mm; the air gap between the second lens and the third lens is 0~0.5mm.

[0024] The first, second, and third lenses are plastic aspherical lenses, and the equation for their aspherical curves is as follows:

[0025] Where Z is the distance from the vertex of the aspherical surface to the optical axis at a height of r; c is the paraxial curvature of the aspherical surface; k is the conic constant; α1, α2, α3, α4, α5, α6, α7, α8, α9, α 10 All are coefficients of higher-order terms.

[0026] The total optical length (TTL) of the lens's optical system satisfies the following relationship with the focal length (f): 2.0 ≤ TTL / f ≤ 2.5; the F-number of the optical system is ≤ 2.0; and the image height (H) of the optical system satisfies the following relationship with the focal length (f): H / f ≥ 1.5. The aperture stop of the optical system is located in front of the first lens, and a filter is provided on the rear side of the third lens.

[0027] The technical specifications achieved by the optical system of the lens of this invention are as follows: Focal length: 3.0 ≤ EFFL ≤ 4.0 mm; Aperture F≤2.0; Field of view: 2w ≥ 81°; Operating band: Infrared band.

[0028] To achieve the above design parameters, the specific design of the optical system adopted in this embodiment is shown in the table below:

[0030] The aspherical coefficients of the aspherical lenses in the optical system of this embodiment are shown in the table below:

[0032] The optical system in this embodiment achieves high resolution, low distortion, low temperature drift, and good image quality by rationally allocating the optical power, surface shape, center thickness of each lens, and on-axis distance between each lens. The total length of the lens is less than 7mm, meeting the requirements of miniaturization design, while also reducing the lens manufacturing cost.

[0033] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A three-piece compact DMS lens characterized by: The lens is provided with a first lens, a second lens and a third lens from an object side to an image side in sequence, and a diaphragm is arranged before the first lens, the first lens is a glass aspherical lens, and the second lens and the third lens are plastic aspherical lenses; the first lens is a meniscus lens with positive refractive power, the object side surface of the first lens is a concave surface, and the image side surface is a convex surface; the second lens is a meniscus lens with positive refractive power, the object side surface of the second lens is a concave surface, and the image side surface is a convex surface; the third lens is a meniscus lens with negative refractive power, the object side surface of the third lens is a convex surface, and the image side surface is a concave surface; the on-axis distance of the optical system of the lens satisfies the following relationship, the air gap between the first lens and the second lens is 0.5-1.0 mm; and the air gap between the second lens and the third lens is 0-0.5 mm.

2. The three-piece compact DMS lens of claim 1, wherein: The focal length of the optical system of the lens is f, and the focal lengths of the first lens, the second lens and the third lens are f1, f2 and f3 respectively, wherein f1, f2 and f3 satisfy the following ratios with respect to f: 1.0<f1 / f<2.0, 0.5<f2 / f<1.0 and -1.0<f3 / f<-0.

5.

3. The three-piece compact DMS lens of claim 1, wherein: The first lens satisfies the relationship: 2.0 ≤ N d ≤ 2.1, V d ≤ 50.0; the second lens satisfies the relationship: 1.5 ≤ N d ≤ 1.8, V d ≥ 50.0; the third lens satisfies the relationship: 1.5 ≤ N d ≤ 1.8, V d ≤ 50.0; where N d is the refractive index, and V d is the Abbe number.

4. The three-piece compact DMS lens of claim 1, wherein: The first lens, the second lens and the third lens are plastic aspherical lenses, and the aspherical curve equation expression is as follows: ， Where Z is the distance from the vertex of the aspherical surface to the optical axis at a height of r; c is the paraxial curvature of the aspherical surface; k is the conic constant; α1, α2, α3, α4, α5, α6, α7, α8, α9, α 10 All are coefficients of higher-order terms.

5. The three-piece compact DMS lens of claim 1, wherein: The total optical length TTL of the optical system of the lens and the focal length f of the optical system satisfy the following relationship: 2.0≤TTL / f≤2.5, and the F number of the optical system is ≤2.

0.

6. The three-piece compact DMS lens of claim 1, wherein: The image height H of the optical system of the lens and the focal length f of the optical system satisfy the following relationship: H / f≥1.5; and a filter is arranged on the rear side of the third lens.

7. The three-piece compact DMS lens of claim 1, wherein: The technical indexes achieved by the optical system of the lens are as follows: Focal length: 3.0≤EFFL≤4.0 mm; Aperture F≤2.0; Field of view angle: 2w≥81°; Working waveband: infrared waveband.

8. The three-piece compact DMS lens of claim 1, wherein: The specific design of the optical system of the lens is shown in the following table: 。 9. The three-piece compact DMS lens of claim 1, wherein: The aspherical coefficients of the aspherical lenses of the optical system of the lens are as follows: 。 10. The imaging method of the three-piece compact DMS lens according to any one of claims 1 to 9, characterized by: The incident light passes through the first lens, the second lens, the third lens and an equivalent glass flat in sequence and is imaged on an IMA imaging plane.

Images