WO2011153990A1 - Optical device having a bifocal optical element and a mirror element - Google Patents

Abstract

The invention relates to a vehicle having an optical device, wherein the optical device is disposed in the interior of the vehicle behind the windshield (5) in the driving direction and detects the exterior, wherein the optical device comprises an image sensor (4) having a surface sensitive to electromagnetic radiation, an objective (1) for projecting electromagnetic radiation onto the sensitive surface of the image sensor (4), a bifocal optical element (8) for simultaneously focusing an image of a region of the windshield (5) and of a region ahead of the vehicle onto two sub-regions of the sensitive surface of the image sensor (4), and a mirror element (S1).

Description

 Optical device with a bifocal optical element and a mirror element

The invention relates to an optical device that can be used as a camera system in a vehicle as environment sensor for driver assistance systems.

Intelligent driver assistance systems often use a camera system as environment sensor, for example, to detect a variety of objects in the traffic.

 The camera system is often located behind the windshield of the vehicle and looks through it. Examples include vehicle cameras for detecting lane markings, night vision cameras or stereo cameras as optical distance sensors. The number and quality of functions, which are realized by the evaluation of the image data of camera systems, has been increased in recent years.

 For example, driver assistance systems are currently used in vehicles that combine intelligent lighting control, traffic sign recognition and lane keeping assistance that use a common camera as an environment sensor.

DE 102004037871 B4 shows a camera system for an assistance system which detects the outer vestibule in the direction of travel of a motor vehicle. By inserting a conversion lens In a partial field of vision in front of the lens of the vehicle camera remote (road scene) and close range (windshield) are imaged on an image sensor. The near field can be imaged by the partial conversion lens or a partial near-vision optics. It is proposed to use an image sensor alternately for an outdoor space assist function and a rain function.

The general approach with a camera to depict a distance and a close range on an image sensor sometimes brings with it some difficulties. The imaging of the near range may be subject to disturbing light influences from the far range, which makes an evaluation of the near range imaging more difficult.

An object of the invention is therefore to provide a cost-effective, stable and reliable optics for a vehicle camera sensor, by which, in particular, disturbing light influences can be minimized.

A further object is to simultaneously increase or guarantee the reliability of the image data captured by the camera system and to realize or facilitate further assistance functions with a camera system.

According to the invention, an optical device is arranged behind the windshield in the interior of a vehicle, which detects the outside in the direction of travel. The optical device comprises an image sensor, an objective, a bi-focal optical element and a mirror element. The image sensor is a semiconductor element with a surface sensitive to electromagnetic radiation, in particular a CCD or CMOS chip. The semiconductor element may be arranged on a printed circuit board.

The objective for projecting electromagnetic radiation onto the sensitive surface of the image sensor preferably comprises at least one lens and a lens holder.

In particular, the bifocal optical element may be a bifocal lens, a plane-parallel plate that lies only in a partial area (lateral) of the imaging beam path, or a continuous element with at least two partial areas of different thickness. The bifocal optical element causes a near optical area, in particular a region of the windshield, to be imaged focused in a first image area of the image sensor and a remote optical area in a second image area of the same image sensor, typically an area in front of the vehicle, i. the vehicle environment.

The mirror element serves, in particular, to project electromagnetic radiation from a defined object area into the objective such that this radiation is imaged in at least one image area of the image sensor. In a vehicle, a camera-based rain sensor may be provided in a preferred embodiment. The images from the first area of the sensitive area of the image sensor (outside of the windshield) are evaluated, whereby rain or dirt particles are detected on the windshield. An output signal for activation may be on a wiper control and / or windscreen cleaning are issued. The images of the second area of the sensitive area of the image sensor (area in front of the vehicle) can be made available to one or more driver assistance systems such as traffic sign recognition and / or lane keeping assistance / warning warning as raw data.

Advantageously, in a vehicle with an optical device, the mirror element is arranged in such a way that electromagnetic radiation falling from an area above the vehicle through the windshield onto the mirror element is directed onto a region of the sensitive surface of the image sensor. As a result, the functionality of an ambient light sensor is preferably realized, which can detect daylight, night and the entrance into a tunnel and controls the dipped beam accordingly.

Known ambient light sensors typically use one each forward and one upward photodiode. In order to determine the brightness in these areas, the mirror element is arranged, for example, as a part of a scattered light diaphragm adjoining the windscreen such that electromagnetic radiation incident on the mirror element from an area above the vehicle through the windshield is reflected by the mirror element , is reflected again at the bottom of the windshield and is directed to an area of the sensitive area of the image sensor. In particular, the region of the scattered light diaphragm adjoining the windshield can be made so smooth that it acts as a mirror element, the area of the lens hood, however, can be designed to be typically very rough to minimize further reflections. Preferably, the electromagnetic radiation reflected by the mirror element is directed to an area of the sensitive area of the image sensor in which the far-field is focused, ideally not superimposed with the image of the far-field corresponding to the area in front of the vehicle. From the image of the area in front of the vehicle, the same image sensor can be used to determine the brightness in the front-facing field of view at the same time. By evaluating the brightness values in both directions, it is possible, for example, to distinguish between gray and white thresholds between day and night or tunnel entry or exit, and to control the vehicle light accordingly. In this way, therefore, the operation of a comparatively simple automatic light control, which automatically activates the dipped beam at low ambient brightness, can additionally be realized, for example, for gene detection and further assistance functions with a common optical device having a single image sensor.

In a preferred embodiment, the mirror element is arranged in such a way that electromagnetic radiation incident on the mirror element from a region of the windshield is imaged in a first subregion of the (first) subarea of the near field image on the sensitive surface of the image sensor and in the second subregion of this subregion the one area of the windshield is shown directly. The mirror element preferably has an opposite pitch angle with respect to the camera field of view in comparison to the inclination of the windshield. The mirror edge is preferably located in the middle of the Nahbereichsabbildung and thus represents a plane of symmetry. Objects on the windshield, such as rain droplets can be represented on the image sensor at this symmetry plane once normal and once mirrored. By comparing the two images, object edges can be better distinguished from interfering light influences, since interfering factors from the far - end range will only occur on one image, and not, for example, in the image reflected by the mirror element. By means of a suitable evaluation of the two near-field images, the quality of the detection of objects in the area of the windshield can thus be further optimized.

In a vehicle with an optical device according to the invention, the mirror element can preferably be designed as a hollow mirror arrangement. By way of the arrangement of hollow mirror elements, electromagnetic radiation which falls from an area of the windshield onto the concave mirror arrangement is reflected at the concave mirror elements, is reflected again at the underside of the windshield and directed to a region of the sensitive area of the image sensor. By virtue of the concave mirror elements preferably integrated into the scattered light diaphragm, the imaging beam path of objects on the windscreen is collimated. The bifocal optical element can do this serve to keep the required radius of curvature of the concave mirror elements small.

In a preferred embodiment, the vehicle comprises a lighting element for illuminating the area of the windshield. Due to the external illumination, objects on the windscreen can be reliably detected, for example even in the dark. As a lighting element can serve in particular a light emitting diode. Advantageous is an illumination with electromagnetic radiation in the infrared wavelength range, since this is not visible to the driver, but can be detected by a corresponding image sensor. According to an advantageous embodiment of the invention, the electromagnetic radiation emitted by the lighting element is coupled via a coupling element {eg a flexible light guide body) into the windshield of the vehicle. Especially in combination with the mirror element, such a coupling element offers a good possibility for distinguishing between near-range and far-field imaging. The lighting is preferably coupled via a light guide with an integrated concave mirror profile in cylindrical design. In the image analysis, the symmetry of the image data can advantageously be used as a parameter for the separation between objects on the windshield and disturbing factors from the environment. Preferably, the mirror element can be designed as part of the coupling element, for example as an (outwardly) reflecting edge of the element, which serves for coupling the radiation into the windshield. Advantageously, the lighting element can also be arranged within the coupling element. In this case, the edge of the coupling-in element can preferably be designed as a double-sided mirror element, ie the radiation emitted by the lighting element is reflected inward, while radiation impinging on the edge from the outside is reflected outwards, in particular for imaging onto the image sensor.

According to a preferred embodiment, the mirror element is arranged below a device for the periodic light passage. The mirror element could be under an LCD array, a mechanical shutter, or another optoelectronic periodic light transmission system. The temporally varied reflection facilitates the identification of the mirrored image on the image sensor.

Preferably, the illumination is modulated by the lighting element. The distinction between the near field and the far field could be supported by a modulated illumination, wherein in particular a lighting coupling into the windshield or a transillumination of the windscreen can be provided by the lighting element. A modulation of lighting can additionally help reliably distinguish near-range imaging. The invention also relates to a method for evaluating image data taken with an optical device according to the invention of a vehicle, wherein the evaluation takes into account the mirror image in order to eliminate disturbances from the far-field imaging in the field of near-field imaging.

The invention will be explained below with reference to exemplary embodiments and figures.

FIG. 1: imaging properties (schematic) of an optical device in a motor vehicle with a bifocal optical element, a mirror element and an image sensor. FIG

Fig. 2: Example of an image taken by the image sensor Fig. 3: Einkopplungselement with mirror element

Fig. 4: Double-sided mirror element with lighting and coupling element

Fig. 5: optical device with concave mirror assembly and lighting element

FIG. 1 schematically shows the imaging properties of an optical device with an objective (1), a bifocal optical element (8), a mirror element (S1) and an image sensor (4) for detecting electromagnetic radiation. shear radiation shown. The image sensor (4) is further provided with a cover glass (3). The optical device is disposed below a windshield (5) of a vehicle. Within the dotted lines lies the field of view of the optical device, which is limited downwards by a lens hood (7).

The illustrated bifocal optical element (8) is a partial optical element, e.g. a plane-parallel glass plate, which fills only a portion of the field of view. Alternatively, in particular a bifocal optical element {8} could be used, which e.g. the image sensor (4) completely covers and has two different thickness subregions. As a result, the illustrated cover glass (3) for the image sensor (4) could be omitted.

The principle for this bifocal optics is based on the axial offset of a non-parallel beam path of a refractive plane surface. The objective (1) is focused in such a way that the distant region (S4) is imaged sharply on the sensitive surface of the image sensor (4) only by the partial optical element (8) and the near region (S2, S3) without the partial optical Element to traverse is shown. The near plane (S2, S3) is focused on the outside of the windshield (5) so that there are raindrops (6) or dirt particles in the corresponding part (T4, T2 The far-range map (S4) is evaluated for camera-based assistance functions, eg lane recognition, traffic sign recognition, etc. The sensitivity of a rain sensor function to a bifocal optical device can be limited by confounding light sources from the far field. A modulated approximately monochromatic illumination and the color filters of the Bayer pattern can be used for signal filtering. For a better differentiation of object edges and interfering light influences, a mirror element (S1) is provided, which can also be combined with an input element for illumination, as illustrated in FIGS. 3 and 4. The mirror element (S1) has an opposite pitch angle to the field of view of the image sensor (4) as the inclined windshield (5).

The beam path of the near-field imaging (S2) via the mirror element (S1), the beam path of the near-field image (S3) without mirror element and the beam path of the far-field imaging (S4) are also shown.

FIG. 2 shows an example of an image taken by the image sensor 4 of an optical device according to the invention. The image shown corresponds to a rotated by 180 ° image that could have been taken in front of the image sensor (4) in Fig. 1. The upper approximately 60 percent of the total image shows the far-field imaging (Tl), which correspond to the beam path (S4) of Fig. 1.

In the remaining lower part of the overall picture are the two near-field images {T2 and T4). The near-field upper map (T2) results from the direct beam path of the near-field map (S3) of Fig. 1. The lower near-field map (T4) is substantially mirrored horizontally, the mirror edge (T3) separates both near-field images (T4, T2). The lower Nahbereichsabbildung (T4) resulting from the beam path of Nahbereichsabbildung (S2) on the mirror element (Sl) of Fig .1.

 The mirror edge (T3) is preferably located in the middle of the Nahbereichsabbildung and thus represents a plane of symmetry. Raindrops (6) on the windshield (5) are on the image sensor {4) at this symmetry plane (T3) once normal and once mirrored imaged. Interference factors from the far-end range, on the other hand, are only displayed in one of the two sub-ranges of the near-field images. The image analysis uses the symmetry of the two near-field images (T2, T4) as a parameter for separation between actual objects (e.g., raindrops (6)) on the windshield (5) and environmental disturbances in a captured image.

Fig. 3 shows a mirror element (Sl), which is designed as part of the coupling element (Bl). For this purpose, a reflective surface is realized as a mirror element (S1) in a desired inclination relative to the windshield (5) as the edge of the illuminating coupling element (B1). Especially in combination with a lighting input element (Bl), the mirror element (S1) is an interesting possibility for distinguishing between near and far range. The lighting coupling can also be done via a light guide with an integrated concave mirror profile in a cylindrical design. 4, an arrangement for coupling a lighting is shown schematically. Behind the windshield (a) is a double-sided mirror element

(d) arranged to emit light emitted from a light emitter having a cylindrical lens as optics (c) onto a concave free plane mirror, i. a concave mirror {b) reflected. From the concave free-form mirror (b), in turn, the light of the light emitter (c) in the windshield

(a) coupled, where it is guided in the area which is imaged by the image sensor (4).

Fig. 5 shows an embodiment of the optical device in a vehicle with an arrangement of concave mirrors {e} as a mirror element. About the arrangement of concave mirror elements electromagnetic radiation (S5), which from a portion of the windshield (5) on the hollow mirror assembly (e) is reflected on the concave reflecting elements is reflected on the underside of the windshield (5) again and on a Directed area of the sensitive surface of the image sensor (4). A bifocal optical element (8) is not shown in FIG. 5, but could, for example, be located inside the objective (1) or be arranged between the objective and the image sensor. By virtue of the concave mirror elements which are preferably integrated into the scattered light diaphragm, the imaging beam path of objects on the windshield is collimated. By designing and aligning the concave mirror arrangement, moreover, the beam path of the near-range imaging (S5) focused in the area of the windshield can, for example, be transferred to another area via the bifocal optical element (8) of the image sensor are referred to as the far-field map (S4). The bifocal optical element (8) helps to keep the required radius of curvature of the concave mirror elements (e) small.

reference numeral

1 lens

 2 main plane of the lens

 3 cover glass

 4 image sensor

 5 windshield

 6 raindrops in one area of the windshield

 7 Lens hood

 8 bifocal optical element

 51 mirror element

 52 Beam path Close-up imaging via mirror element

 53 Beam path Close-up imaging

 54 beam path long range imaging

 55 Beam path Close-up imaging via a hollow mirror arrangement

 Tl image area of the far area picture

 T2 image area of the near-field direct imaging

T3 mirror axis or symmetry plane

 T4 image area of the near-field image over the

 mirror element

 Bl coupling element

 a windshield

 b concave freeform mirror (concave mirror)

 c Lighting element with cylindrical lens

 d two-sided mirror element

 e concave mirror arrangement

 LED lighting element

Claims

claims 1. vehicle having an optical device, wherein the optical device in the interior of the vehicle behind the windshield (5) in the direction of travel, the outer space is arranged to detect, wherein the optical device comprises  an image sensor (4) having a surface sensitive to electromagnetic radiation,  an objective (1) for projecting electromagnetic radiation onto the sensitive surface of the image sensor (4),  a bifocal optical element (8) for simultaneous focused imaging of a region of the windshield (5) and an area in front of the vehicle on two partial areas of the sensitive area of the image sensor (4) and  - a mirror element (Sl). 2. vehicle with an optical device according to claim 1, characterized in that the image data from the first region of the sensitive surface of the image sensor (4) are evaluated, with rain and / or dirt particles on the windshield (5) are detected and an output signal to a Wiper control and / or window cleaning control can be output. 3. vehicle with an optical device according to claim 1 or 2, wherein the mirror element (Sl) in such a way is arranged, that electromagnetic radiation, which falls from an area above the vehicle through the windshield (5) on the mirror element (Sl) is directed to a portion of the sensitive surface of the image sensor (4). 4. Vehicle with an optical device according to claim 1 or 2, wherein the mirror element (Sl) is arranged such that electromagnetic radiation which falls from a region of the windshield (5) on the mirror element (Sl), in a first sub-area (T4 ) of the subarea of the near field image is imaged on the sensitive surface of the image sensor (4) and in the second subregion (T2) of this subarea an area of the windshield is imaged directly. 5. Vehicle with an optical device according to claim 1 or 2, wherein the mirror element (Sl) is designed as a concave mirror arrangement (s). 6. A vehicle with an optical device according to one of the preceding claims, wherein the optical device comprises a lighting element (LED) for illuminating the area of the windshield. 7. Vehicle with an optical device according to claim 6, wherein the optical device has a coupling element (B1) for coupling in from the lighting element. ment (LED) emitted electromagnetic radiation in the windshield (5). 8. vehicle with an optical device according to claim 7, wherein the mirror element (Sl) is designed as part of the coupling element (Bl). 9. vehicle with an optical device according to one of the preceding claims, wherein the mirror element (Sl) is arranged under a device for periodic light transmission. 10. Vehicle with an optical device according to one of the preceding claims, wherein the illumination is modulated. 11. A method for evaluating image data recorded with an optical device of a vehicle according to claim 4, wherein in the evaluation the mirror image (T4) is taken into account in order to eliminate disturbances from the far-field imaging in the sub-image of the near-field image.