CN214623043U - Lens system, imaging module and depth camera - Google Patents

Abstract

The utility model discloses a lens system, imaging module and depth camera, including first lens, second lens, third lens and fourth lens; the first to third lenses have positive focal power, the fourth lens has negative focal power, and the first to fourth lenses satisfy the following conditions: -20<f₁/f2<9；0.3<f₂/f₃<16；‑1.7<f₃/f₄<‑0.1；‑0.9<f₁₂₃/f₄<‑0.05；‑75<f₁/f₂₃₄<15；1.52<N_d<1.95；0.5<f/TL<0.9; wherein f is the effective focal length of the lens system; f. of₁Is the effective focal length of the first lens; f. of₂Is the effective focal length of the second lens; f. of₃Is the effective focal length of the third lens; f. of₁₂₃Is the combined focal length of the first lens, the second lens and the third lens; f. of₂₃₄Is the combined focal length of the second lens, the third lens and the fourth lens; nd is the refractive index of the lens material for D light; TL is the distance from the object plane to the image plane of the first lens on the optical axis. The utility model discloses lens system, formation of image module and degree of depth camera can realize the distortion compensation of big light ring, have solved the inhomogeneous problem of speckle density, can obtain good imaging quality when guaranteeing compact structure.

Description

Lens system, imaging module and depth camera

Technical Field

The utility model relates to an optics and electron technical field, concretely relates to lens system, imaging module and degree of depth camera.

Background

The existing optical lens is often applied to electronic devices such as cameras and projectors, and particularly for consumer-grade electronic devices such as mobile phones and computers, the optical lens is often small in size, low in cost and stable in performance, so that the design difficulty is high. In recent years, with the development of consumer-grade 3D imaging electronics, such as TOF depth cameras, optical lenses are increasingly widely used.

TOF depth cameras typically project a speckle pattern outwardly through a lens system, a Diffractive Optical Element (DOE), via light from a light source, which is received by an imaging module and then used to generate a depth image. For a speckle light source, because the coverage area of an image speckle field angle (FOV) is obtained by copying and expanding a central speckle block by a DOE, when the field angle of the speckle area is increased, a very serious distortion phenomenon can be generated, so that the speckles at the center of a receiving end of an imaging module are dense, the speckles at corners are sparse, the uniformity of a depth map is influenced finally, and the uniformity of the depth map is poor.

The above background disclosure is only for the purpose of assisting understanding of the inventive concepts and technical solutions of the present invention, and does not necessarily belong to the prior art of the present patent application, and should not be used for evaluating the novelty and inventive step of the present application in the case that there is no clear evidence that the above contents are disclosed at the filing date of the present patent application.

SUMMERY OF THE UTILITY MODEL

The utility model discloses a main aim at overcomes prior art not enough, provides a lens system, formation of image module and degree of depth camera to solve at least one kind problem among the above-mentioned background art problem.

The utility model discloses a reach above-mentioned purpose and propose following technical scheme:

a lens system comprises a first lens, a second lens, a third lens and a fourth lens which are sequentially arranged along the incident direction of a light beam; wherein the first lens, the second lens, and the third lens have positive optical power, the fourth lens has negative optical power, and the first lens, the second lens, the third lens, and the fourth lens satisfy the following condition:

-20<f₁/f2<9；

0.3<f₂/f₃<16；

-1.7<f₃/f₄<-0.1；

-0.9<f₁₂₃/f₄<-0.05；

-75<f₁/f₂₃₄<15；

1.52<N_d<1.95；

0.5<f/TL<0.9；

wherein f is the effective focal length of the lens system; f. of₁Is the effective focal length of the first lens; f. of₂Is said second lens hasAn effective focal length; f. of₃Is the effective focal length of the third lens; f. of₁₂₃Is a combined focal length of the first lens, the second lens, and the third lens; f. of₂₃₄Is a combined focal length of the second lens, the third lens, and the fourth lens; nd is the refractive index of the lens material for D light; TL is the distance from the object plane to the image plane of the first lens on the optical axis.

In some embodiments, both the object plane and the image plane of the fourth lens are concave at a paraxial region, and at least one surface between the object plane and the image plane of the fourth lens is aspheric.

In some embodiments, an aperture stop is further included, the aperture stop being disposed between any two adjacent lenses.

In some embodiments, an aperture value of a lens group formed by the first lens, the second lens, the third lens and the fourth lens satisfies: fno < 1.2.

In some embodiments, the first lens, the second lens, the third lens, and the fourth lens are plastic lenses.

In some embodiments, the fourth lens is a glass lens.

The utility model discloses a another technical scheme does:

an imaging module comprises an image sensor, a filtering unit and a receiving optical element; wherein the receiving optical element is configured to receive at least a portion of the speckle pattern reflected back from the target object and direct the at least a portion of the speckle pattern onto the image sensor; the receiving optical element comprises the lens system of any of the embodiments.

In some embodiments, the filtering unit is an infrared filter for filtering out background light or stray light.

The utility model discloses a technical scheme does yet:

a depth camera comprises an imaging module, a projection module, a processing electrical appliance and a bracket, wherein the imaging module, the projection module, the processing electrical appliance and the bracket are arranged in the scheme of the embodiment; the projection module and the imaging module are arranged on the bracket at a preset baseline distance.

In some embodiments, the projection module comprises a light source consisting of one or more lasers for projecting an encoded speckle pattern into a target space; the imaging module collects photons in the speckle pattern reflected by the target object and outputs photon signals; the processor synchronizes the trigger signals of the projection module and the imaging module to calculate the flight time required by the photons from emission to reflection to reception, so as to obtain the depth information of the target object.

The utility model discloses technical scheme's beneficial effect is:

compared with the prior art, the utility model discloses lens system, formation of image module and degree of depth camera can realize the distortion compensation of big light ring, have solved the inhomogeneous problem of speckle density, can obtain good imaging quality when guaranteeing compact structure.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive exercise.

FIG. 1 is a functional block diagram of a depth camera according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of an imaging module according to another embodiment of the present invention;

fig. 3 is a schematic view of an optical path structure of an imaging module according to another embodiment of the present invention.

Detailed Description

In order to make the technical solution of the present invention better understood, the technical solution of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative efforts shall belong to the protection scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, unless expressly stated or limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can include, for example, fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meaning of the above terms in the present invention can be understood according to specific situations by those skilled in the art.

It will be further understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner" and "outer" refer to an orientation or positional relationship as shown in the drawings, which are used for convenience in describing and simplifying the invention, and do not indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be considered limiting of the invention.

For the convenience of understanding, the depth camera and the imaging module are described first, and finally, the lens system is further described.

Referring to fig. 1, fig. 1 is a schematic view of a depth camera according to an embodiment of the invention, in which a depth camera 100 includes a projection module 10, an imaging module 20, and a processing device 13; the projection module 10 and the imaging module 20 are arranged on the bracket at a preset baseline distance; wherein, the projection module 10 includes a light source 101 composed of one or more lasers for projecting the encoded speckle pattern into the target space, and reflecting the encoded speckle pattern back to the imaging module 20 through the target object 40 in the target space; the imaging module 20 includes an image sensor 201 for collecting photons in the reflected speckle pattern and outputting a photon signal; the processor 30 is connected to the projection module 10 and the imaging module 20, and is configured to synchronize the trigger signals of the projection module 10 and the imaging module 20 to calculate a flight time required for receiving the photons from the emitting direction to the reflecting direction, so as to obtain depth information of the target object.

Specifically, the projection module 10 includes a light source 101, an emission optical element 102, a driver 103, and the like. The light source 101 may be a Light Emitting Diode (LED), a Laser Diode (LD), an Edge Emitting Laser (EEL), a Vertical Cavity Surface Emitting Laser (VCSEL), or the like, or may be a one-dimensional or two-dimensional light source array composed of a plurality of light sources. The light beam projected by the light source 111 may be visible light, infrared light, ultraviolet light, or the like. The light source 101 projects a light beam outward under the control of the driver 103. In one embodiment, the light source is an infrared laser light source, such as a 940nm band, the speckle points may be arranged in a quadrilateral or hexagonal pattern, and correspondingly, the imaging module is an infrared camera of the corresponding band.

The emission optical element 102 receives the light beam emitted from the light source 101 and projects the light beam to a target region after shaping. In one embodiment, the transmit optical element 102 receives a pulsed light beam from the light source 101 and modulates the pulsed light beam by encoding, such as diffraction, refraction, reflection, etc., and then projects an encoded speckle pattern, such as a focused light beam, a flood light beam, a structured light beam, etc., into space. In one embodiment, the emitting optical element 102 is a lens or a lens group.

The imaging module 20 includes an image sensor 201, a filter unit 202, and a receiving optical element 203; wherein receiving optics 203 is configured to receive at least a portion of the speckle pattern reflected back from the target object and direct the at least a portion of the speckle pattern onto image sensor 201; the filtering unit 202 is used for filtering out background light or stray light; in one embodiment, the image sensor 201 is a TOF sensor, the filter unit 202 is a filter (e.g., an infrared filter), and the receiving optics 203 includes a lens system.

Referring to fig. 2 and 3, as an embodiment of the present invention, the lens system includes a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4 sequentially arranged along the incident direction of the light beam 205, wherein the first lens L1, the second lens L2, and the third lens L3 have positive focal power, and the fourth lens L4 has negative focal power. In order to obtain larger negative distortion compensation and ensure the best imaging quality while the structure is compact, the lens system satisfies the following conditions:

-20<f₁/f2<9；

0.3<f₂/f₃<16；

-1.7<f₃/f₄<-0.1；

-0.9<f₁₂₃/f₄<-0.05；

-75<f₁/f₂₃₄<15；

1.52<N_d<1.95；

0.5<f/TL<0.9；

wherein f represents the effective focal length of the lens system; f. of₁Denotes an effective focal length of the first lens L1; f. of₂Denotes a second lens L₂The effective focal length of; f. of₃Represents the effective focal length of the third lens L3; f. of₁₂₃Denotes a combined focal length (unit: mm) of the first lens L1, the second lens L2, and the third lens L3; f. of₂₃₄Denotes a combined focal length (unit: mm) of the second lens L2, the third lens L3, and the fourth lens L4; nd denotes a refractive index of the lens material for D light. The D light can be written as D-line, also called D line, and the wavelength is 587 nm; TL denotes a distance from the object plane to the image plane of the first lens L1 on the optical axis.

In the embodiment shown in fig. 2, the object plane of the first lens L1 is convex at the paraxial region, and the image plane of the first lens L1 is concave at the paraxial region; the object plane and the image plane of the fourth lens element L4 are both concave at paraxial regions, and at least one surface of the fourth lens element L4 between the object plane and the image plane is aspheric.

In some embodiments, the lens system further comprises an aperture stop, which may be disposed as desired, such as between any two adjacent lenses.

In some embodiments, the aperture value of the four lens groups of the lens system is Fno, and Fno <1.2 is satisfied, so that the imaging plane has sufficient and appropriate illumination intensity.

In one embodiment, all lenses of the lens system are plastic lenses, and the focal length of the lens group is reduced by optimizing system parameters and being affected by temperature over-cooling or over-heating. The plastic lens may be made of PMMA (chemical name of polymethylmethacrylate, i.e., organic glass, commonly called acryl), PC (Polycarbonate), and APEL 5014. In some embodiments, to some imaging module that the temperature variation is great, the lens of lens system can adopt the glass material that receives the temperature to influence for a short time, and the glass material can improve thermal stability, and its characteristics such as high temperature resistant, corrosion-resistant, resistant fish tail can protect whole lens system not by the fish tail in assembly, transportation, the use, is difficult for being separated by wind, destruction under adverse circumstances such as high temperature, low temperature, high light, sand blown by the wind to lens system's life has been prolonged. However, the glass material will cause cost increase, and in order to consider cost and performance, in some embodiments, the fourth lens L4 may be configured as a glass lens so that the lens system can have stable focal position and focal length at different temperatures, and the other three lenses are not limited, and glass or plastic may be used.

For convenience of description, the object side of the first lens L1 is denoted as S3; the image-side surface of the first lens L1 is denoted as S4; the object-side surface of the second lens L2 is denoted as S5; the image-side surface of the second lens L2 is denoted by S6; the object-side surface of the third lens L3 is denoted as S7; the image-side surface of the third lens L3 is denoted by S8; the object side of the fourth lens L4 is denoted as S9; the image-side surface of the fourth lens is denoted as S10.

The following specific example shows a parametric design of a lens system, it should be understood that the parametric design is for illustration only and does not limit the scope of the present invention.

Table 1 below is an exemplary lens system surface coefficient:

TABLE 1 surface coefficients of lens systems

The aspherical surface curve equation of each lens is as follows:

wherein z is a position value in the optical axis direction at a position of height h with the surface vertex as a reference; c represents a curvature of the lens surface near the optical axis, and is an inverse of a curvature radius (R) (c 1/R); r is the curvature radius of the lens surface close to the optical axis; h is the perpendicular distance of the lens surface from the optical axis, k is the conic constant; and A2, A4, A6, A8, A10, A12, A14, A16 and … … are high-order aspheric coefficients.

Table 2 below is an exemplary lens system aspheric coefficient design:

TABLE 2 aspherical coefficients

In the parametric design example described above, the lens system is capable of operating at F/1.2 and is capable of achieving a 72 ° field angle with an optical distortion of-25.6%. Under the exemplary parameter design, the lens system has better distortion compensation for a large-aperture imaging lens, and can solve the problem of uneven speckle density.

The above description is only exemplary of the present invention and should not be taken as limiting the scope of the present invention, as any modification, equivalent replacement or improvement made within the spirit and principle of the present invention should be included in the present invention.

In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction. Although embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope of the invention as defined by the appended claims.

Claims (10)

1. A lens system, characterized by: the device comprises a first lens, a second lens, a third lens and a fourth lens which are sequentially arranged along the incident direction of a light beam; wherein the first lens, the second lens, and the third lens have positive optical power, the fourth lens has negative optical power, and the first lens, the second lens, the third lens, and the fourth lens satisfy the following condition:

-20<f₁/f2<9；

0.3<f₂/f₃<16；

-1.7<f₃/f₄<-0.1；

-0.9<f₁₂₃/f₄<-0.05；

-75<f₁/f₂₃₄<15；

1.52<N_d<1.95；

0.5<f/TL<0.9；

wherein f is the effective focal length of the lens system; f. of₁Is the effective focal length of the first lens; f. of₂Is the effective focal length of the second lens; f. of₃Is the effective focal length of the third lens; f. of₁₂₃Is a combined focal length of the first lens, the second lens, and the third lens; f. of₂₃₄Is a combined focal length of the second lens, the third lens, and the fourth lens; nd is the refractive index of the lens material for D light; TL is the distance from the object plane to the image plane of the first lens on the optical axis.

2. The lens system of claim 1, wherein: the object plane and the image plane of the fourth lens are both concave surfaces at the position near the optical axis, and at least one surface between the object plane and the image plane of the fourth lens is an aspheric surface.

3. The lens system of claim 1, wherein: the lens further comprises an aperture diaphragm, and the aperture diaphragm is arranged between any two adjacent lenses.

4. The lens system of claim 1, wherein: the aperture value of a lens group formed by the first lens, the second lens, the third lens and the fourth lens satisfies: fno < 1.2.

5. The lens system of claim 1, wherein: the first lens, the second lens, the third lens and the fourth lens are plastic lenses.

6. The lens system of claim 1, wherein: the fourth lens is a glass lens.

7. The utility model provides an imaging module which characterized in that: comprises an image sensor, a filter unit and a receiving optical element; wherein the receiving optical element is configured to receive at least a portion of the speckle pattern reflected back from the target object and direct the at least a portion of the speckle pattern onto the image sensor; the receiving optical element comprising a lens system according to any one of claims 1 to 6.

8. The imaging module of claim 7, wherein: the filtering unit is an infrared filter used for filtering background light or stray light.

9. A depth camera, characterized by: comprising the imaging module, the projection module, the processor and the bracket of claim 7; the projection module and the imaging module are arranged on the bracket at a preset baseline distance.

10. The depth camera of claim 9, wherein: the projection module comprises a light source consisting of one or more lasers for projecting an encoded speckle pattern into a target space; the imaging module collects photons in the speckle pattern reflected by the target object and outputs photon signals; the processor synchronizes the trigger signals of the projection module and the imaging module to calculate the flight time required by the photons from emission to reflection to reception, so as to obtain the depth information of the target object.

Images