EP2666055A1

EP2666055A1 - Camera arrangement for a motor vehicle

Info

Publication number: EP2666055A1
Application number: EP12708713.8A
Authority: EP
Inventors: Marcus Eickhoff; Frank BLÄSING; Gregor BÖHNE; Ralf Böbel
Original assignee: Leopold Kostal GmbH and Co KG
Current assignee: Leopold Kostal GmbH and Co KG
Priority date: 2011-01-21
Filing date: 2012-01-19
Publication date: 2013-11-27
Also published as: CN103329039A; CN103329039B; WO2012098192A1; US9525808B2; DE102011009075A1; DE102011009075B4; US20130162827A1

Abstract

A camera arrangement includes a camera and a prism. The camera includes a camera sensor having an array of pixels. The prism is arranged between a window pane such as a vehicle windshield and the camera sensor. Optical properties of the camera sensor and the prism are matched to one another such that a maximum broadening of a light beam due to dispersion of the prism lies within one pixel of the camera sensor.

Description

Camera arrangement for a motor vehicle

The invention relates to a camera arrangement for a motor vehicle with a camera arranged in the vehicle interior behind a vehicle window and with a beam guide element which is arranged between the vehicle window and the camera, which has or forms a prism, wherein the camera has an electronic camera sensor with a pixel array.

Such a camera arrangement is known from German published patent application DE 10 2008 020 954 A1.

Camera arrangements with a vehicle window looking through the camera, for example, the lane and / or

Traffic sign recognition used. In modern passenger cars, the front windshield, referred to as a windshield, is located at a relatively shallow angle (about 20 ° to 25 °) to the horizon for aerodynamic and aesthetic reasons. Therefore, one in horizontal

Direction of incident light beam when entering such a vehicle window strongly broken.

Normally, the light beam is again strongly refracted when exiting the vehicle window. However, it is known that a prismatic

Light guide can be coupled without refraction or with only a small refraction to the inside of the vehicle window, so that the beam path is modified in an advantageous manner. However, such light guide can also cause geometric distortions and disturbing color aberrations.

The geometric distortions are both compressions or strains and also curvatures of the camera images. These are relatively unproblematic because they are subsequently eliminated mathematically can. The compensation of color errors of prism arrangements, however, can be very expensive. Mostly there are several prisms

provided, which consist of different, and sometimes expensive materials or are to be arranged in a geometrically complex manner to each other.

It has set itself the task of creating a particularly simple and inexpensive generic camera arrangement for a motor vehicle, which has little or no color aberrations.

This object is achieved in that the optical properties of the camera and the prism are matched to one another such that caused by the dispersion of the prism within the wavelength range detected by the camera maximum

Beam broadening on the camera sensor is within a pixel size of the pixel array.

The camera assembly according to the invention is particularly inexpensive to produce, since it manages with only a single prism.

The invention is based on the consideration that blurring or chromatic aberrations are only recognizable by the dispersion of the prism when a point of an object detected by the camera is imaged on different pixels of the camera sensor of the camera. Therefore, aberrations of optical elements go unnoticed as long as they remain below the pixel size.

The optically effective surfaces of an optical prism are usually so flat that no discernible defect is created by the residual unevenness. In addition, the material of an optical prism is usually so homogeneous that this also causes no recognizable error. So if a simple prism (as opposed to a

dispersion compensating arrangement of a plurality of prisms) is used in front of the lens or in front of the lens of the camera, a deterioration of the image quality is to be expected mainly by the dispersion properties of the prism material. Different wavelengths are deflected differently by the prism, so that then the angles of incidence on the camera sensor are different. So that the light rays of all

Wavelengths that are relevant for the generation of a pixel, sufficiently well mapped to a single pixel, the

Prism angle should be so small that the difference of the angle of incidence on the camera sensor remains below the resolution limit.

The optical properties of the camera and the prism are therefore suitable to match. In this case, go from the prism of the refractive index of the prism material and its change

(Dispersion relation) over the wavelength range of the light detected by the camera, the angle of incidence of the light, and the value of the refractive angle of the prism. On the part of the camera, the size or the distance of the pixels on the camera sensor is particularly relevant.

These values must be coordinated in such a way that the values determined by the

Dispersion of the prism maximum possible beam broadening can not be greater than a pixel of the camera sensor. In particular, the

Prism angle deliberately chosen so that the desired prism effect, so for example, the light beam deflection or the geometric compression, as large as possible, but the point broadening on the camera sensor by the chromatic error is still sufficiently small. In the following the invention will be illustrated with reference to the drawing and explained in more detail. Show it 1 shows a schematically illustrated camera arrangement, FIG. 2 shows a sketch of the resolution capability of a camera sensor, FIG. 3 shows a sketch of the beam expansion through the dispersion of the camera

Prism material.

FIG. 1 shows the basic arrangement of the components of FIG

Camera arrangement according to the invention. Primarily, the structure and function principle should be clarified; therefore, the illustrated

Components with respect to a real constructive implementation neither large nor angularly true to each other shown.

The arrangement consists of a prism 3 and a camera 7, wherein the camera 7 is arranged such that it looks through a vehicle window 2, that receives light from the outside of the vehicle window 2. In this case, the beam path 1 extends from the vehicle window 2 to the camera 7 through the prism 3 and through an optical medium 4 located between the prism 3 and the camera 7. For the sake of simplicity let it be assumed that air is provided as the optical medium 4.

The camera 7 consists of at least one lens 6 and a light-registering camera sensor 5. The lens 6 has at least one focusing-acting lens. Of course, further optical, electronic or mechanical components, in particular a housing, may also be components of the camera 7.

To illustrate the beam path, the course of three parallel incident light beams 1 is shown in Figure 1, which meet approximately horizontally on the outside of the inclined against the direction of incidence vehicle window 2. Upon entering the vehicle window 2, the light beams 1 are refracted towards the Scheibenlot. On the inside of the vehicle window 2, the prism 3 is arranged. The prism 3 preferably has an identical or similar refractive index as the vehicle window 2, and is optically coupled to the vehicle window 2, so that in the transition region between the vehicle window 2 and the prism 3 virtually no angular deflection of the light beams 1 takes place. The after passing through the prism 3 still parallel to each other extending light beams 1 are focused by the camera lens 6 on the camera sensor 5 of the camera 7. The prism 3 shown in FIG. 1 has a relatively small size

refractive angle ß and therefore does not have the wedge shape typical for prisms, but is designed as a plate with non-plane-parallel major surfaces. You can also think of this prism 3 as a one-piece

Imagine a connection of a plane-parallel plate and a very acute-angled prism wedge. The refractive angle β is about 2 ° in the prism 3 sketched here.

FIG. 2 illustrates the resolving power of the camera sensor 5 of a camera. Representative of the lens 6, a single lens 6 'is shown. Dashed lines indicate the main plane of the lens 6 'and the optical axis of the camera. At a distance of the focal length f of the lens 6 ', a camera sensor 5 in cross section recognizable. It is assumed that the camera sensor 5 consists of a pixel array p, not shown as an individual part.

A light beam incident on the lens 6 'at an angle to the optical axis as a mid-point beam impinges on the surface of the camera sensor 5 unbroken, ie at an equally large angle to the optical axis, and is there on the kth pixel counted by the sensor center of the camera sensor 5 shown. From Figure 2, the following relationship can be read: tan '= x / f = kp / f

A numerical example: with a focal length f = 10 mm and a pixel size p = 10 μιη tan is 1 ° = k ^* 0.010 / 10, ie a resolution of the camera of n = 17,455 pixels per degree for small angles'.

The principle of the invention is explained below with reference to FIG. FIG. 3 firstly illustrates, in a greatly simplified, purely qualitative representation, the development of chromatic aberrations in an arrangement with a prism.

As is known, due to the dispersion properties of the prism material, incident light in a prism (not shown here) is decomposed into the spectral colors contained in the light. For example, when white light strikes the prism at a given angle of incidence, the different colors or wavelengths exit the prism at different angles of deflection. The angle range covered thereby can be estimated for visible light by the deflection angle ocbiau of the shortest wavelength light refracted the most and the deflection angle _ro t of the weakest refracted longwave light. For the camera arrangement, however, it is not the spectrum of the incident light that is relevant, but only that of the light which can also be detected by the camera arrangement. Due to the transmission properties of eg the vehicle window 2 or the objective 6 and the spectral

Sensitivity of the camera chip 5, the spectrum of the detected light is normally reduced compared to the spectrum of the incident light. Analogously, ocbiau and _ro t therefore mean the deflection angles of the light with the shortest and the longest detectable wavelengths.

The resulting numerical values for these deflection angles depend not only on the dispersion profile of the prism material used but also on the geometry of the prism and on the angle of incidence of the light into the primate 3 and can be determined computationally or experimentally for the particular arrangement.

Due to the angular splitting, the dispersion-broadened beam is thus reduced to a width of .mu.m on the camera sensor

Δχ = (tan biomautan a _ro t) ^* f.

So that the dispersion of the prism 3 is not distracting, it is provided that the components outlined in FIG

Camera arrangement coordinated so that the

Dispersion broadening smaller than the pixel size p of the camera sensor 5 remains:

(tan abiau tan a _red ) ^* f <p

This can thereby suitable choice of the prism material, the

Prismengeometrie, the spectral properties of the camera arrangement and the resolution of the camera sensor 5 can be achieved.

The resolution caused by the pixel size p represents a sensible limit for the entire camera optics. The lens 6 '(or the objective 6) does not need to have a resolution which lies below the pixel size p. Also errors of other optical elements are irrelevant, as long as the whole

Image error remains below the pixel size p.

The camera arrangement described here thus avoids chromatic errors without requiring compensation measures with complex multi-part prism arrangements. reference numeral

1, light rays (beam path)

2 vehicle window

3 prism

4 optical medium

5 camera sensor

6 (camera) lens

6 'lens

7 camera, 'angle

«Red,« biow deflection angle

ß refractive angle f focal length

k number of pixels

p pixel size

x distance

Claims

claims

1 . Camera arrangement for a motor vehicle with a camera (7) arranged in the vehicle interior behind a vehicle window (2) and with a beam guide element which is arranged between the vehicle window (2) and the camera (7), which has or forms a prism (3), wherein the camera (7) has an electronic camera sensor (5) with a pixel array, characterized in that the optical properties of the camera (7) and of the prism (3) are matched to one another in such a way that the dispersion caused by the dispersion of the prism (3) within the area covered by the camera (7)

Wavelength range caused maximum beam broadening on the camera sensor (5) is within a pixel size of the pixel array.

2. Camera arrangement according to Claim 1, characterized in that the wavelength range detected by the camera (7) substantially corresponds to the wavelength range which is visible to the human eye.

3. Camera arrangement according to claim 1, characterized in that the refractive angle (ß) of the prism (3), and the focal length f of the

Camera lens (6) and the pixel size p of the camera sensor (5) in such a way are coordinated with each other so that the camera arrangement maintains the following relationship for each point of the pixel array:

(tan ccbiau - tan _red ) ^* f <p where biau and a _ro t indicate the deflection angles, under which a point of the object to be imaged for maximum shortwave and maximum longwave light from the camera detected by the (7)

Wavelength range is imaged on the camera sensor (5).

Camera arrangement according to Claim 1, characterized in that the beam guiding element contains, in addition to the optically active surfaces of the prism (3), elements which serve for fixing and / or aligning the camera (7).

Camera arrangement according to claim 1, characterized in that the beam guiding element contains, in addition to the optically active surfaces of the prism (3), elements which serve to suppress scattered light.

Camera arrangement according to claim 1, characterized in that the prism (3) has a refractive angle (β) of at most 4 °.