WO2023118950A1

WO2023118950A1 - Multiwavelength optical road condition sensor with single emission point

Info

Publication number: WO2023118950A1
Application number: PCT/IB2021/062330
Authority: WO
Inventors: Sina FELLA; Andreas Baumgartner; Jorge Miguel NUNES SANTOS CABRAL; José António AZEVEDO GONÇALVES; José Miguel SOUSA GOMES; António GOMES LOPES; Andre Agostinho MONTEIRO PEREIRA; Pedro José DA SILVA FERREIRA ARADE DE MACEDO; Stefan Kuntz
Original assignee: Bosch Car Multimedia Portugal, S.A.; Universidade Do Minho
Priority date: 2021-12-22
Filing date: 2021-12-27
Publication date: 2023-06-29

Abstract

The present application describes a multiwavelength optical road condition sensor with a single emission point. The proposed sensor is comprised of at least two laser light sources, preferably with four, but not limiting, which are arranged and configured to emit multimode laser lights over a reflector shape element in a predetermined incidence angle; characterized by the incidence angle being configured to combine the emitted multimode laser lights into a single combined multimode laser light beam perpendicular to the emitted multimode laser lights.

Description

Multi wavelength optical road condition sensor with single emission point

Technical Field

The present application describes a multiwavelength optical road condition sensor with a single emission point.

Background art

In order to ensure safe automated driving, the friction of the road must be known. In general, the friction is mainly influenced by the "intermediate medium" between road and tire, i.e., by the presence of water and its states (solid: ice, snow, liquid: layer thickness) , leaves, etc. The detection of such media can be done by various sorts of devices, such as acoustic, microwave or optical sensors.

Near infrared sensors are one example of such sensors, which, operating in an 800nm - 3000nm optical range, quantify the diffuse or direct reflection of each emitted wavelength (or wavelength range) . The determined quantities significantly differ depending on wavelength due to the strength of water absorption lines of the different aggregate states of water. Therefore, dry and non-dry road conditions can be distinguished, intermediate states such as ice slurry categorized, and water layer thicknesses determined. For the achievement of this result, typically intensities, ratios of intensities and/or the polarization state get evaluated, either by comparisons, thresholds or machine learning. This optical principle is already known from the state of the art , being disclosed for instance in documents DE2712199 , and DE19506550 .

Summary

The present invention describes a multiwavelength single emission point optical sensor comprising at least two laser light sources arranged and configured to emit multimode laser lights over a reflector shape element in a predetermined incidence angle ; characteri zed by the incidence angle being configured to combine the emitted multimode laser lights into a single combined multimode laser light beam .

In a proposed embodiment of present invention, the multiwavelength single emission point optical sensor comprises a set of di f fusing and or focussing lens elements , arranged over the reflector shape element and ahead of the single combined multimode laser light beam, configured to widen, narrow, scatter, redirect , reshape or modi fy the polari zation state of the single combined multimode laser light beam .

Yet in another proposed embodiment of present invention, the single combined multimode laser light beam is perpendicular to the emitted multimode laser lights .

Yet in another proposed embodiment of present invention, the multiwavelength single emission point optical sensor comprises a set of collimating lenses and/or lens spacers arranged between the at least two laser light sources and the reflector shape element . Yet in another proposed embodiment of present invention, the single combined multimode laser light beam is emitted over a surface .

Yet in another proposed embodiment of present invention, the surface is a road which comprises at least one of a gravel , concrete and asphalt roads .

Yet in another proposed embodiment of present invention, the surface reflects di f fuse or direct quantities of the single combined multimode laser light beam that allows the detection of di f ferent state conditions of the surface of the road .

Yet in another proposed embodiment of present invention, the di f ferent state conditions of the surface o f the road comprise determining the presence of liquid water, quanti fying the liquid water layer thickness .

Yet in another proposed embodiment of present invention, the di f ferent state conditions of the surface o f the road comprise the surface friction coef ficient .

Yet in another proposed embodiment of present invention, the surface friction coef ficient is determined via indirect approach, between database correlation of road state and friction, or via an accelerometer sensor .

Yet in another proposed embodiment of present invention, the multimode laser lights comprise multiple wavelengths .

Yet in another proposed embodiment of present invention, the reflector shape element comprises at least two highly reflective surfaces in the near-infrared wavelength range that enable low optical power loss , improved beam shape control and simple alignment of the optical path of the single combined multimode laser light beam .

Yet in another proposed embodiment of present invention, the multiwavelength single emission point optical sensor comprises at least one photodiode monitor configured to determine the output power of the emitted multimode laser lights and/or the output power of the single combined multimode laser light beam .

Yet in another proposed embodiment of present invention, the at least two laser light sources and the reflector shape element are thermally coupled, enabling the temperature stabili zation of the at least two laser light sources and of the single combined multimode laser light beam .

Yet in another proposed embodiment of present invention, the thermal coupling of at least two laser light sources with the reflector shape element comprises at least a temperature control device , installed between a heatsink element ( 80 ) and a pressure plate , said pressure plate being pressured against a thermal material interface .

General Description

The present application describes a multiwavelength optical road condition sensor with a single emission point .

One of the main constructional challenges of such optical sensors is related with the optics design, particularly, when several light sources , typically lasers or LEDs , are used .

The proposed solution for the above-mentioned sensors based on a single emission point comprises several advantages , in particular :

1 . Only one optical window is needed for all the emitting light sources , including a single solution for dirt protection;

2 . The optical influence of dirt and other contaminants is the approximately the same for all the emitted l ight sources , which enables computational compensation methods .

3 . Anisotropically scattering surfaces will scatter di f ferently depending on the incident angle of the light beam, therefore it is preferable that all the light sources are combined into one single beam .

There are numerous ways to achieve the combination of the light beams , for instance by beam splitters , dichroic mirrors or dispersive optical elements .

However, the present invention discloses a di fferent approach based on the combination of several light beams to a single beam by a mechanical concept with low optical power loss .

The herein proposed apparatus enables a low optical power loss with an improved beam shape control and simple alignment of the optical path . The most common application of the device is intended to light source packages , being also possible to scale down for use with light source dies through miniaturi zation . The current invention resorts to the use of a reflector element of pyramidal shape that is highly reflective for the wavelengths used in the sensor . The pyramidal reflector shape element is placed in between the several light sources , in particular in their light path, in order to approximate a single beam leaving the sensor . Preferred light sources are lasers , LEDs or SLEDs .

Dependent on the light source , one or more lenses can be mounted between each light source and the pyramidal reflector shape element in order to shape the emitting light beam, for example collimating it . Eventually, lens spacers might need to be added to fine tune the focal distances of said beams .

Brief description of the drawings

For better understanding of the present application, figures representing preferred embodiments are herein attached which, however, are not intended to limit the technique disclosed herein .

Fig . 1 - illustrates the constructive concept of the

Multiwavelength optical road condition sensor with a single emission point , wherein the reference numbers relate to :

100 - multiwavelength single emission point optical system;

10 - multimode laser light diode A arranged in Transistor Outline ( TO) package ;

11 - emitted multimode laser light A;

12 - resulting ( reflected and re-shaped) light beam A from the multimode laser light diode A; 15 set of laser and collimating lens and/or lens spacers ;

16 - collimating lens ;

50 - four- face pyramidal reflector shape element ;

60 - di f fusing element / lens .

Fig . 2 - illustrates the resulting combination of four emitted multimode lasers over a four- face pyramidal reflector shape element , wherein the reference numbers relate to :

11 - emitted multimode laser light A by multimode laser light diode A;

21 - emitted multimode laser light B by multimode laser light diode B ;

31 - emitted multimode laser light C by multimode laser light diode C ;

41 - emitted multimode laser light D by multimode laser light diode D;

50 - four- face pyramidal reflector shape element ;

60 - di f fusing element / lens ;

200 - combined laser light beams from the four multimode laser light diodes A, B, C and D .

Fig . 3 - illustrates the overall aspect of the

Multiwavelength optical road condition sensor with a single emission point embedded in a housing, wherein the reference numbers relate to :

100 - multiwavelength single emission point optical system;

200 - combined light beams from four multimode laser .

Fig . 4 - illustrates the top view of the cut section on Figure 1 which includes the pyramidal-shaped reflector and the at least two laser diodes (here presented with four laser diodes arranged in a circular pattern creating a cross pattern) where the reference numbers relate to:

100 - multiwavelength single emission point optical system;

15 - set of laser and collimating lens and/or lens spacers .

Fig. 5 - illustrates the constructive concept of the Multiwavelength optical road condition system (100) with a single emission point, in a vertical cut perspective, wherein the reference numbers relate to:

50 - four-face pyramidal reflector shape element;

60 - diffusing element / lens;

70 - temperature control device;

71 - thermal material interface;

72 - pressure plate;

80 - heatsink.

Description of Embodiments

With reference to the figures, some embodiments are now described in more detail, which are however not intended to limit the scope of the present application.

A particular embodiment of the disclosed multiwavelength optical road condition system (100) with a single emission point, supported by the illustrations of Figure 1 and Figure 2, comprises a multiwavelength single emission point optical system (100) and a four-face pyramidal reflector shape element (50) wherein at least one light source A (10) emits a light beam A (11) over said reflector shape element. In the illustrated embodiment, the emitted light beam, a multimode laser light A (11) , is correctly aligned with one face of the pyramidal reflector (50) in a proposed incident angle of 45°, being the resulting beam A (12) reflected by the pyramidal shape element perpendicular to the original incident multimode laser A (11) , achieving a total of 90° angular change with regard to the initial direction of the propagated light beam A (11) . Since the reflector shape element (50) , in one of the preferred embodiments, resorts to the use a four-face pyramidal shape element in order to obtain the proposed combination of multiwavelength laser lights over a single emission point (200) according to the depicted Figure 2, additional multimode laser light diodes, multimode laser light diode B, multimode laser light diode C and multimode laser light diode D will be further arranged in a cross shaped arrangement, visible in Figure 4, so that each of their emitted light matches independently one face of the reflector shape element (50) .

In the proposed embodiment of Figure 1, the four-face pyramidal reflector shape element (50) , triangular prism, comprises highly reflective properties in the near-infrared wavelength range, for example, one of a gold-coated aluminium and/or glass materials. Alternatively, the pyramidal element (50) can be etched or machined from silicon, preferably along one of the symmetry axes of silicon.

Each light source of the multiwavelength single emission point optical system (100) , i.e., multimode laser diodes, may be attached to its overall structure by means of bolts, springs and/or conical rings, allowing further precision adjustment of said light sources, allowing the correct positioning and alignment of the emitted light beams (11, 21, 31, 41) with respect to the angle of incidence on the pyramidal element (50) .

In order to further shape the resulting combined emitted beam (200) , a diffusing, a focussing lens element and or the pyramidal surface (60) can be used over the reflected beam leaving the pyramid. In the following, we refer to this element as "diffuser". Such an element can widen, narrow, scatter, redirect, or, more generally, reshape the outgoing beam, as well as change the polarization state. It is preferred to widen the beam to a size larger than the asphalt grains, in order to average over several grains.

In one of the preferred embodiments, the multiwavelength single emission point optical system (100) comprises at least one photodiode monitor close to the diffuser and/or the optical window and/or the light sources, in order to monitor the output power of the light sources to enable normalization during signal processing of the detected light that is reflected and/or scattered by the road surface.

In one of the preferred embodiments of the single emission point optical system (100) the laser emitting sources and the pyramidal reflector shape element (50) are thermally coupled, i.e., combined in one assembly element with good thermal conductivity.

This combined assembly, illustrated in Figure 5, allows a good thermal coupling between the light sources like laser diodes or LEDs over the reflector shape element (50) to a temperature control device (70) like a heater or a Peltier element. For instance, and for this particular embodiment, it is possible to resort to the use of a heating and/or cooling device such as Peltier elements. Through a thermal material interface (71) directly connected to a pressure plate (72) which is directly pressured against the Peltier element (70) , it is possible to ensure the temperature stabilization, wherein the excess heat produced by the set is dissipated through the heatsink element (80) . This arrangement is necessary to keep all the light sources operating on the same stable temperature to guarantee a stable signal emission. Additionally, a good thermal coupling allows a fast adaption of the temperature of light sources via the temperature control device (70) . The settlement base of the reflective element (50) , as well as the light source holders, will preferably comprise a thermally well conductive material to allow the stabilization of the light sources' temperature.

Figure 2 illustrates the resulting beam path (200) of a system (100) with four light sources (11, 21, 31, 41) , i.e., a combined light beam from four multimode laser diodes A, B, C and D, a four-face pyramidal reflector shape element (50) , and a diffusing element (60) .

The multiwavelength single emission point optical system (100) can resort to the use of a separate detector sensor, or instead of using said separate detector, one could also place the detecting photodiode behind the four-face pyramidal reflector shape element (50) or located in the surrounding of any of the light sources (11, 21, 31, 41) . In this particular case, the detector should be protected against internal reflections.

Instead of using a complete pyramidal reflector (50) , i.e., all the faces, another embodiment can comprise only selected parts of the pyramid (50) being placed ahead of the light sources. This is especially interesting for miniaturizing.

Claims

1. Multiwavelength single emission point optical system (100) comprising at least two laser light sources arranged and configured to emit multimode laser lights over a reflector shape element (50) in a predetermined incidence angle; characterized by the incidence angle being configured to combine the emitted multimode laser lights into a single combined multimode laser light beam (200) .

2. Multiwavelength single emission point optical system (100) according to the previous claim, comprising a set of diffusing and or focussing lens elements (60) , arranged over the reflector shape element (50) and ahead of the single combined multimode laser light beam (200) , configured to widen, narrow, scatter, redirect, reshape or modify the polarization state of the single combined multimode laser light beam (200) .

3. Multiwavelength single emission point optical system (100) according to any of the previous claims, wherein the single combined multimode laser light beam (200) is perpendicular to the emitted multimode laser lights.

4. Multiwavelength single emission point optical system (100) according to any of the previous claims, comprising a set of collimating lenses and/or lens spacers (15) arranged between the at least two laser light sources and the reflector shape element (50) .

5. Multiwavelength single emission point optical system (100) according to any of the previous claims, wherein the single combined multimode laser light beam (200) is emitted over a surface.

6. Multiwavelength single emission point optical system (100) according to any of the previous claims, wherein the surface is a road which comprises at least one of a gravel, concrete and asphalt roads.

7. Multiwavelength single emission point optical system (100) according to any of the previous claims, wherein the surface reflects diffuse or direct quantities of the single combined multimode laser light beam (200) that allows the detection of different state conditions of the surface of the road.

8. Multiwavelength single emission point optical system (100) according to any of the previous claims, wherein the different state conditions of the surface of the road comprise determining the presence of liquid water, quantifying the liquid water layer thickness.

9. Multiwavelength single emission point optical system (100) according to any of the previous claims, wherein the different state conditions of the surface of the road comprise the surface friction coefficient.

10. Multiwavelength single emission point optical system (100) according to any of the previous claims, wherein the surface friction coefficient is determined via indirect approach, between database correlation of road state and friction, or via an accelerometer sensor.

11. Multiwavelength single emission point optical system (100) according to any of the previous claims, wherein the multimode laser lights comprise multiple wavelengths.

12. Multiwavelength single emission point optical system (100) according to any of the previous claims, wherein the reflector shape element (50) comprises at least two highly reflective surfaces in the near-infrared wavelength range that enable low optical power loss, improved beam shape control and simple alignment of the optical path of the single combined multimode laser light beam (200) .

13. Multiwavelength single emission point optical system (100) according to any of the previous claims, comprising at least one photodiode monitor configured to determine the output power of the emitted multimode laser lights and/or the output power of the single combined multimode laser light beam (200) .

14. Multiwavelength single emission point optical system (100) according to any of the previous claims, wherein the at least two laser light sources and the reflector shape element (50) are thermally coupled, enabling the temperature stabilization of the at least two laser light sources and of the single combined multimode laser light beam (200) .

15. Multiwavelength single emission point optical system (100) according to any of the previous claims, wherein the thermal coupling of at least two laser light sources with the reflector shape element (50) comprises at least a temperature control device (70) , installed between a

15 heatsink element (80) and a pressure plate (72) , said pressure plate (72) being pressured against a thermal material interface (71) .

16