KR20240029129A - Optical system for TOF camera - Google Patents

Abstract

The present invention provides an optical system used in a TOF (Time of Flight) camera capable of 3D sensing. An optical system according to the present invention includes a first lens having positive refractive power; a second lens having negative refractive power; a third lens having negative refractive power; It includes a fourth lens having positive refractive power, and the first lens, second lens, third lens, and fourth lens are arranged in order from the object side to the image side, and the conditional expression 2.0 < FOV/TTL < 3.0 (FOV: of the optical system) Satisfies the angle of view (°), TTL: total length of the optical system (mm)).
According to the present invention, an optical system optimized for a vehicle-mounted TOF camera for driver condition monitoring can be provided. In addition, according to the present invention, the reflected light collection efficiency of the TOF camera is improved by implementing a very bright optical system with F-no 1.5 or less, so that the driver's image can be captured more clearly inside the vehicle. In addition, according to the present invention, an optical system suitable for a driver monitoring system can be provided by implementing a field of view of about 37 to 38 degrees that can intensively photograph the driver's face. Additionally, according to the present invention, the size of a vehicle-mounted TOF camera can be minimized by implementing a total optical length (TTL) of around 16 mm.

Description

Optical system for TOF camera}

The present invention relates to an optical system for a Time of Flight (TOF) camera capable of 3D sensing, and specifically to an optical system for an infrared TOF camera suitable for use in monitoring the driver's condition when mounted on a vehicle.

A TOF (Time of Flight) camera is a camera that can very accurately detect the depth of an object's surface by calculating the time it takes for light emitted from a light source to reflect on an object and return in units of pixels of the image sensor.

These TOF cameras are used to detect the distance to individual objects in an image or to detect the surface curvature of an object in three dimensions in fields such as autonomous driving, virtual reality (VR), augmented reality (AR), and motion recognition-based controllers. can be used

In particular, recently, interest in TOF cameras has been growing in the field of driver monitoring systems installed in vehicles.

The driver monitoring system is a system that can prevent accidents by quickly identifying emergency situations such as driver drowsiness, inattention, or unconsciousness and taking appropriate measures such as warnings and braking. Recently, as competition among automobile manufacturers has intensified, The number of applied cases is increasing.

Methods for determining the driver's condition in the driver monitoring system include, for example, a method for determining the driver's condition by detecting and analyzing biosignals such as the driver's pulse, breathing, and brain waves, and a method for determining the driver's face or eye images. It is known that camera-based monitoring systems are preferred over biometric signal utilization methods that require sensors to be attached to or close to the driver's body.

In order to accurately determine the driver's condition using camera images, it is necessary to accurately detect 2-dimensional or 3-dimensional changes in the position of feature points on the driver's curved face. This requires a TOF camera with excellent 3-dimensional sensing capabilities in the driver monitoring system. is widely used.

Meanwhile, in order for a TOF camera to demonstrate stable performance, the type of light source, field of illumination (FOI), and 3D recognition algorithm must be optimally designed, as well as excellent optical performance and reflected light collection efficiency. There is a need to design a highly optimal optical system.

Republic of Korea Patent No. 10-2433563 (announced on August 18, 2022) Republic of Korea Patent No. 10-2433668 (announced on August 18, 2022)

The present invention was conceived against this background, and its purpose is to provide an optimal optical system suitable for a vehicle-mounted TOF camera for monitoring driver status.

To achieve this object, one aspect of the present invention includes: a first lens having positive refractive power; a second lens having negative refractive power; a third lens having negative refractive power; It includes a fourth lens having positive refractive power, and the first lens, second lens, third lens, and fourth lens are arranged in order from the object side to the image side, and the conditional expression 2.0 < FOV/TTL < 3.0 (FOV: optical system Provides an optical system that satisfies the angle of view (°), TTL: total length of the optical system (mm)).

The optical system according to an aspect of the present invention may further satisfy the conditional expression 0.5 < f /f1 < 1.5 (f: focal length of the entire optical system (mm), f1: focal length of the first lens L1 (mm)) .

Additionally, the optical system according to one aspect of the present invention may further satisfy the conditional equation 1.0 < TTL / f < 2.0 (TTL: total length of the optical system (mm), f: focal length of the entire optical system (mm)).

In addition, the optical system according to one aspect of the present invention has the conditional expression 0.5 < f/f34 < 2.0 (f: focal length of the entire optical system (mm), f34: composite focal length of the third lens (L3) and the fourth lens (L4) (mm)) can be more satisfied.

Additionally, the F number of the optical system according to one aspect of the present invention may be 1.5 or less.

Additionally, in the optical system according to one aspect of the present invention, the first lens is a lens whose object side is convex and the image side is concave, the second lens is a lens whose object side is convex and the image side is concave, and the third lens is a lens whose object side is concave. The lens may be concave and the image side may be convex, and the fourth lens may be a lens whose object side is convex and the image side may be concave or flat.

Additionally, in the optical system according to one aspect of the present invention, the first lens, the second lens, and the fourth lens may each be a glass lens whose both sides are spherical, and the third lens may be a glass lens whose both sides are aspherical.

Additionally, in the optical system according to one aspect of the present invention, the refractive index (Nd) of the first lens may be smaller than the refractive index (Nd) of the second lens and greater than the refractive index (Nd) of the fourth lens.

According to the present invention, an optical system optimized for a vehicle-mounted TOF camera for driver condition monitoring can be provided.

In addition, according to the present invention, the reflected light collection efficiency of the TOF camera is improved by implementing a very bright optical system with F-no 1.5 or less, so that the driver's image can be captured more clearly inside the vehicle.

In addition, according to the present invention, an optical system suitable for a driver monitoring system can be provided by implementing a field of view of about 37 to 38 degrees that can intensively photograph the driver's face.

Additionally, according to the present invention, the size of a vehicle-mounted TOF camera can be minimized by implementing a total optical length (TTL) of around 16 mm.

1A is a configuration diagram of an optical system according to a first embodiment of the present invention.
1B is an aberration diagram of an optical system according to the first embodiment of the present invention.
Figure 2a is a configuration diagram of an optical system according to a second embodiment of the present invention.
Figure 2b is an aberration diagram of an optical system according to a second embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

First, Figures 1A and 1B respectively show the configuration and aberration diagram of the optical system according to the first embodiment of the present invention, and Figures 2A and 2B respectively show the configuration and number of the optical system according to the second embodiment of the present invention. It shows the path to recovery.

The optical system according to an embodiment of the present invention includes first lenses L1 to fourth lenses L4 arranged in order from the object side to the image side, as shown in FIGS. 1A and 2A.

Specifically, the first lens L1 may have positive refractive power, and may be a lens with a convex object side and a concave image side.

The second lens L2 may have negative refractive power, and may be a lens in which the object side is convex and the image side is concave.

The third lens L3 may have negative refractive power and may be a lens in which the object side is concave and the image side is convex.

The fourth lens L4 has positive refractive power and may be a lens with a convex object side and a concave or flat image side.

Meanwhile, in the optical system according to the embodiment of the present invention, both surfaces of the first lens (L1), second lens (L2), and fourth lens (L4) are spherical, and both surfaces of the third lens (L3) are aspherical. It is desirable to be

Additionally, the first lens (L1), the second lens (L2), the third lens (L3), and the fourth lens (L4) are all made of glass and may have different refractive indices (Nd). In this case, the refractive index (Nd) of the first lens (L1) is preferably smaller than the refractive index (Nd) of the second lens (L2) and larger than the refractive index (Nd) of the fourth lens (L4).

The aperture STOP may be placed in front of or around the first lens L1. Additionally, a cover glass (CG) may be disposed between the fourth lens (L4) and the image sensor.

Additionally, in the optical system according to an embodiment of the present invention, the infrared filter used in a general imaging optical system may be omitted. This is because vehicle-mounted TOF cameras mainly use light sources in the 920-960 nm band of near-infrared light, which has little interference from sunlight, so if an infrared filter is installed, infrared reflected light may not reach the image sensor. However, it is not necessarily limited to this, and instead of an infrared filter, a band-pass filter (BPF) that passes light in a specific wavelength range may be installed inside the cover glass (CG).

Meanwhile, the optical system according to the first and second embodiments of the present invention is preferably designed to satisfy the following conditional equations 1 to 4 in order to secure excellent performance and minimize the overall length while implementing a bright F number suitable for a TOF camera.

<Conditional expression 1>

0.5 < f /f1 < 1.5

f: Focal length of the entire optical system (mm)

f1: Focal length of the first lens (L1) (mm)

Conditional expression 1 above relates to the focal length of the entire optical system and the focal length of the first lens (L1). If the f /f1 value is larger than the upper limit, it becomes difficult to secure a short overall length, and if it is smaller than the lower limit, the optical system is composed of multiple lenses. It becomes difficult to do.

<Conditional expression 2>

1.0 < TTL / f < 2.0

TTL: Total length of optical system (mm)

f: Focal length of the entire optical system (mm)

Conditional equation 2 above relates to the overall length and focal length of the optical system. If the TTL/f value is greater than the upper limit, the total length becomes too long, making miniaturization of the optical system difficult, and if it is less than the lower limit, the refractive power of the lens is insufficient, making it difficult to secure optical performance. Lose.

<Conditional expression 3>

0.5 < f/f34 < 2.0

f: Focal length of the entire optical system (mm)

f34: Composite focal length of the third lens (L3) and fourth lens (L4) (mm)

Conditional expression 3 above relates to the focal length of the entire optical system and the combined focal length of the third lens (L3) and fourth lens (L4). If the f/f34 value is larger than the upper limit, it becomes difficult to secure a short overall length, and if the f/f34 value is larger than the upper limit, it becomes difficult to secure a short overall length. If so, it becomes difficult to construct a bright optical system.

<Conditional expression 4>

2.0 < FOV/TTL < 3.0

FOV: angle of view of optical system (°)

TTL: Total length of optical system (mm)

Conditional equation 4 above relates to the angle of view and total length of the optical system. If the FOV/TTL value is larger than the upper limit, it becomes difficult to secure an appropriate viewing angle, and if it is smaller than the lower limit, the refractive power of the lens is insufficient, making it difficult to secure optical performance.

Table 1 below illustrates specific design specifications of the optical system according to the first and second embodiments that satisfy all of the above-described conditional expressions 1 to 4.

[Table 1]

The data for each example provided to calculate the values in Table 1 are as follows, and the optical system configurations of the first and second examples are as shown in FIGS. 1A and 2A, respectively.

Table 2 below shows the design specifications of the optical system according to the first embodiment - the lens surface shape, radius of curvature (mm), thickness (mm), lens spacing (mm), refractive index (Nd), and Abbe number (Vd) of each lens. etc., and Table 3 shows the aspherical coefficients applied to each lens surface of the third lens L3 of the optical system according to the first embodiment.

[Table 2] Design specifications of the first embodiment

[Table 3] Aspherical coefficient of the first example

Additionally, Table 4 below shows the design specifications of the optical system according to the second embodiment, and Table 5 shows the aspherical coefficients applied to each lens surface of the third lens L3 of the optical system according to the second embodiment.

[Table 4] Design specifications of the second embodiment

[Table 5] Aspherical coefficient of the second embodiment

Meanwhile, the shape of the aspherical lens in each embodiment can be calculated through the equation below.

[Equation]

In the above equation, Z is the distance from the vertex of the lens in the optical axis direction, h is the distance perpendicular to the optical axis, c is the reciprocal of the radius of curvature at the vertex of the lens, K is the Conic constant, A4, A6, A8, A10, A12, A14, A16,,,, are aspheric coefficients, as shown in Tables 3 and 5, respectively.

Meanwhile, Figures 1b and 2b show aberration diagrams of optical systems according to the first and second embodiments, respectively, through which it can be seen that astigmatism and distortion are good in each embodiment.

In addition, according to an embodiment of the present invention, the reflected light collection efficiency of the TOF camera can be greatly improved by implementing a very bright optical system with an F number of 1.5 or less, and by implementing a viewing angle of about 37 to 38, it is possible to see the driver's face in the vehicle. You can take pictures clearly. Additionally, by implementing a short overall length (TTL) of around 16mm, it is possible to provide an optical system suitable for small TOF cameras mounted on vehicles.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be implemented in various forms by modification or modification. Modified or modified embodiments of the present invention are also disclosed in the claims described later. If the technical idea is included, it is natural that it falls within the scope of the rights of the present invention.

L1: 1st lens L2: 2nd lens L3: 3rd lens
L4: 4th lens STOP: Aperture CG: Cover glass

Claims (8)

a first lens having positive refractive power;
a second lens having negative refractive power;
a third lens having negative refractive power;
a fourth lens having positive refractive power;
An optical system comprising: a first lens, a second lens, a third lens, and a fourth lens are arranged in order from the object side to the image side, and satisfies the following conditional expression.
2.0 < FOV/TTL < 3.0
(FOV: angle of view of the optical system (°), TTL: total length of the optical system (mm)) According to paragraph 1,
An optical system characterized by satisfying the following conditional expression.
0.5 < f /f1 < 1.5
(f: focal length of the entire optical system (mm), f1: focal length of the first lens (L1) (mm)) According to paragraph 1,
An optical system characterized by satisfying the following conditional expression.
1.0 < TTL / f < 2.0
(TTL: total length of the optical system (mm), f: focal length of the entire optical system (mm)) According to paragraph 1,
An optical system characterized by satisfying the following conditional expression.
0.5 < f/f34 < 2.0
(f: focal length of the entire optical system (mm), f34: composite focal length of the third lens (L3) and fourth lens (L4) (mm)) According to any one of claims 1 to 4,
An optical system characterized by an F number of 1.5 or less According to any one of claims 1 to 4,
The first lens is a lens whose object side is convex and the image side is concave,
The second lens is a lens whose object side is convex and the image side is concave,
The third lens is a lens whose object side is concave and the image side is convex,
The fourth lens is an optical system characterized in that the object side is convex and the image side is concave or flat. According to clause 6,
The first lens, the second lens, and the fourth lens are glass lenses whose both sides are spherical, and the third lens is a glass lens whose both sides are aspherical. In clause 7,
The refractive index (Nd) of the first lens is smaller than the refractive index (Nd) of the second lens and greater than the refractive index (Nd) of the fourth lens.