WO2008037766A1 - Fibre-optic sensor device - Google Patents

Abstract

The invention relates to a fibre-optic sensor device comprising a fibre-optic cable with a light source coupled to a first end of said cable, a light detector coupled to a second end of said cable and means for identifying a deformation based on a modification of the intensity of the light received by the fibre-optic cable. The aim of the invention is to develop a fibre-optic cable of the aforementioned type, whilst simplifying the construction, thus permitting cost-effective production. To achieve this, light of several frequencies or wavelengths (?<SUB>r</SUB>, ?<SUB>b</SUB>, ?<SUB>g</SUB>) is coupled into the first end (3) of the fibre-optic cable (2), the light detector (8) that is coupled to the fibre-optic cable (2) at the second end (7) is designed to evaluate the frequency-selective intensity and the light emission regions (12) on the fibre-optic cable (2) are designed to be selectively effective in accordance with the frequencies or wavelengths (?<SUB>r</SUB>, ?<SUB>b</SUB>, ?<SUB>g</SUB>) that are coupled into the first end (3).

Description

description

Fiber optic sensor device

The present invention relates to a fiber optic sensor device comprising an optical fiber having a light source coupled at a first end and a light detector coupled to the optical fiber at a second end, and means for detecting a deformation based on a change in the intensity of the light received by the optical fiber.

Without limiting its field of application, the present invention will be described below with reference to the automotive sector. Due to the high system requirements coupled with high cost pressure due to the high sales figures, the automotive and motor vehicle sector is an economically very important area of application. Alternative fields of application in aircraft technology or in architecture and the like are generally not excluded.

Fiber-optic sensor devices of the aforementioned type are known, for example, from WO 94/29671 A1. Today, they are used equally for slow as well as fast-moving bending or deformation processes and are therefore also used in modern passenger vehicle construction. For example, a rapid detection of a collision of a motor vehicle with a pedestrian or cyclist by such sensors to initiate so-called active safety measures, such as caused by pyrotechnic elements or an electric drive inclinations of a hood executed.

On the basis of the teaching of WO 94/29671 A1, the applicant has developed a fiber-optic sensor device by means of which a shape of a shock absorber on a motor vehicle is transferred. wakes up and thus a kind of accidental deformation can be detected. Thus, in the case of a crash, a distinction can be made between a collision with a pedestrian and, for example, a dustbin or a traffic sign on the basis of a deformation. The fiber-optic sensor is constructed using four to 16 optical fibers which have been mechanically scratched or chemically defined at certain areas on their lateral surface. Thus, light emission surfaces or areas are created with a variety of forms. Fiber-optic sensor devices of the type mentioned regularly have light-emitting diodes as the light source, each of which is connected to an optical fiber, generally less than 2 m long, in the form of a polymeric optical fiber or polymer optical fiber, or POF for short.

It is an object of the present invention to further develop a fiber optic sensor device of the type mentioned simplifying its structure and thereby also create opportunities for cheaper production.

This object is solved by the features of the independent claim. Further advantageous features of developments of the invention are the subject of the dependent claims.

According to the invention, an optical sensor device of the type mentioned above is characterized in that at a first end of the optical fiber light of several frequencies is coupled, which is formed on the optical fiber at a second end coupled light detector for frequency-selective intensity evaluation and the light emission regions on the optical fiber in Tuning to the coupled-in frequencies at the first end are formed frequency-selectively acting.

This can be arranged over the length of even a single optical fiber a plurality of light emission regions which are different from each other, as they each only for one Frequency or a narrow frequency band act as light emission areas. Other frequencies are not substantially impeded by these light emission regions in propagation within the optical fiber. The construction of a fiber optic sensor device with determination of a type of a respective deformation is thereby considerably simplified.

In a preferred embodiment of the invention, the light emission regions are configured as wavelength-selective-acting as so-called Bragg gratings. For the production of such filters highly accurate working methods are known, by which, however, an optical fiber itself is not mechanically damaged. Since every damage to the fiber acts as a predetermined breaking point, its reliability substantially increases the reliability, especially in the case of the different strong vibration and torsional loads on optical fibers in automotive technology.

Advantageously, the optical fiber is formed as a polymeric optical see fiber or POF, which is provided with direct-write with respect to at least one refractive index n manipulated light emission region. The direct writing on or in a POF is z. B. from the field of micro-photolithography for the production of structures on silicon wafers by means of laser and is now using the achieved accuracy of images in this new field of application.

Preferably, the light of several frequencies is coupled by a corresponding broadband emitting LED at the first end of the optical fiber. In this case, the light detector at the second end of the optical fiber is preferably designed as a so-called rbg sensor in coordination with the wavelength-selective light-emitting regions. Thus, in one embodiment of the invention to both

Ends of the optical fiber to provide or couple only an opto-electrical device. Further features and advantages of the invention are given below with description of embodiments with reference to the figures of the drawing. In the drawing show in schematic form:

Figure 1 shows an embodiment of a fiber optic sensor device with a single optical fiber, broadband emitting LED, a trained for frequency-selective intensity evaluation light detector and three wavelength-selective light emission regions;

FIG. 2 shows a schematic illustration of the function of a fiber optic sensor device according to the prior art;

FIG. 3 shows a known embodiment of a fiber optic sensor device with a plurality of optical fibers according to FIG. 2 to provide an overall device capable of localizing and determining a type of respective deformation;

4a shows a representation of a basic structure and the operating principle of an optical fiber with end-side circuits according to the embodiment of Figure 1 with exemplary beam path for selective attenuation of light of a particular wavelength.

FIG. 4b shows a representation analogous to FIG. 4a with an exemplary beam path for the selective attenuation of light of a second specific wavelength;

FIG. 4c: a representation analogous to the two preceding figures with an exemplary beam path for the selective attenuation of light of a third specific wavelength; Figure 5a: a sketch of the arrangement according to the figures 4a-c with ideal undamped transmission of light of all wavelengths and

FIG. 5b shows a sketch of the arrangement analogous to the representation of FIG. 5a with an indication of a selective signal weakening as a result of a deformation of the optical fiber.

Throughout the various exemplary embodiments and illustrations, the same reference numerals and designations are used below for the same functional or assembly groups and method steps.

FIG. 3 shows a prior art fiber optic sensor device 1. The fiber-optic sensor device 1 comprises an optical fiber 2, which is coupled at a first end 3 of the optical fiber 2 in a coupling region 4 to a light source 5 with an end face 6 and at a second end 7 to a light detector 8. Not shown are circuit electronics and means for detecting a deformation in the region of a sensitive zone 9 based on a change in the intensity of the light received from the optical fiber 2 in the light detector 8. This sensitive zone 9, the u. a. is realized by so-called High or Modes filter or HOMF as a scattering and / or loss range, is arranged between the feed by the light source 5 and a reversal 10 at a reversal point over a section.

Such a fiber-optic sensor device 1 therefore senses a bending of the optical fiber 2 on the basis of intensity deviations and can thus advantageously be used as a crash sensor in a passenger vehicle in areas of the body which are deformed in the event of accidents involving pedestrians or cyclists. To effectively take active safety measures to improve the protection of an injured person To be able to take a person, for example, an increase in an impact angle with the creation of a softer collecting structure in the hood, even a small deformation by such a sensor must be detected quickly and easily.

For cost reasons, in a known sensor device 1 light-emitting diodes LED as light sources 5 at about λ = 660 nm together with appropriately matched photodetectors as light detector components 8 are used. In order to be able to detect a type of deformation on the basis of such a device 1, four to 16 separate sensor devices 1 are combined, as indicated in the figure of FIG. 3 on the basis of three such sensor devices 1 in a bundling. Here, the length L of the optical fibers 2 in the present example case is about 1.5 m. The sensitive zones 9 of the individual fibers 2 are arranged offset from one another in such a way that they form a sensor region 11. The sensor area 11 is in an accident under action of a force U with an indicated in sketched

Way sickle-shaped distribution with respect to its sub-regions 9 deformed to different degrees. Partial deformations can be determined from the different weakenings of a light intensity resulting from each fiber 2 in comparison to a normal case without deformation in a region 9, to which each fiber 2 can also be assigned a location. This means that a deformation that is currently occurring as a result of the accident can be determined quickly and reliably, piece by piece, from individual results.

However, the device complexity for a sufficiently high-resolution localization and shape determination according to FIG. 3 also increases when optical fibers 2 bundled into cables or fiber ribbons are used, proportional to the number of sensitive subregions 9. FIG. 1 shows an exemplary embodiment that satisfies this rule breaks through with simple means. Here, a fiber optic sensor device 1 comprises a Zige POF optical fiber 2, which is supplied or fed at the first end 3 of a broadband emitting light emitting diode. The optical fiber 2 has a light detector 8 designed for frequency-selective intensity evaluation and three wavelength-selective light emission regions 12. These light emission regions 12 are implemented in the present embodiment as a wavelength filter in the form of Bragg gratings. The filter effect is brought about by regionally limited changes of a refractive index n in the optical fiber 2 in certain structures, wherein these

Refractive index changes are defined by direct writing or similar methods. Each of these filters has a respective tuning to one of the wavelengths λ _r , λ _b , λ _g . In the present case, the light source 5 emits light in the visible spectrum and the frequencies of the wavelengths λ _r , λ _b , λ _g lie in the range of the visible colors red R, blue B and green G.

This type of filters and corresponding manufacturing processes, such. As the direct writing or the photo-inscription for writing a defined structure in a waveguide with high accuracy in particular using a laser to produce refractive index changes by deviations in the material density, are known in the field of telecommunications and there for wavelength multiplex or Wavelength domain multiple access, WDM for short, adapted for fiber and polymer technology. For the production of such frequency-selectively acting light emission regions 12 on the optical fiber 2, therefore, the optical fiber 2 itself no longer has to be damaged on its cladding or cladding and thus mechanically weakened.

The sequence of FIGS. 4 a to 4 c again shows the mode of action of the above-described fiber-optic bending and deformation sensor device 1 in schematic form for the three selected frequencies with the respectively associated wavelengths λ _r , λ _b , λ _g . FIG. 4a is a diagram Position of a basic structure and the operating principle of an optical fiber 2 with end-side circuits according to the embodiment of Figure 1 with exemplary beam path for selective attenuation of light only the predetermined wavelength. For the sake of clarity, only two exemplary propagation paths are shown exclusively for light of the wavelengths λ _r , which are capable of propagation in the multimode fiber 2 in total reflection toward the core region. A first path 13 extends through the fiber section shown by way of example from the light source 5 to the detector 8. In this case, this first path 13 also extends through a selectively acting with respect to the wavelength λ _b light emission region 12. However, since this light emission region 12 exclusively to the wavelength λ _b selectively acts as a loss region, the light of wavelength λ _r passes this light emission region 12 substantially without attenuation and continues on the path 13 shown.

In contrast, in the case of a path 14: Here, light of the wavelength λ _r after two total reflections strikes a light emission region 12 which is tuned exactly to the wavelength λ _r . The light on this path 14 is completely removed from the fiber 2 by decoupling it into the outer space.

FIGS. 4b and 4c show illustrations analogous to FIG. 4a with exemplary beam paths based on the paths 15, 16, 17, 18 for the selective attenuation of light of a second and third predetermined wavelength λ _b , λ _g . The mode of operation is always the same, so that in a rbg sensor as a one-piece photodetector 8, a radiation intensity in an unbent normal state can finally be determined for each of these wavelengths.

Figure 5a shows a schematic diagram of the arrangement according to the figures 4a-c in ideal undamped transmission of light of all relevant here wavelengths λ _r, λ _b, λ _g with an exemplary Intensity distribution of these wavelengths, as it is recorded on the rbg detector 8. FIG. 5b shows a sketch of the arrangement analogous to the representation of FIG. 5a with an indication of a selective signal weakening as a result of a deformation of the optical fiber 2, as has already been outlined in FIG. 3 in the known device 1 with three optical fibers 2 for three sensitive zones 9. The deformation of Figure 5b has been chosen so small that only the wavelength λ _r undergoes a weakening of the intensity. Already the quasi adjacent arranged frequency selective for the color blue B acting light emission region 12 is no longer affected by the deformation, so that from only occurring for the wavelength λ _r signal attenuation on a deformation of low expansion just at the location of the light emitting region 12 for the wavelength λ _r can be closed. The construction of the

Device 1 according to FIG. 5b, however, is significantly less complicated than was the case in the known device 1 according to FIG.

In this embodiment, the light source 5 used is a white light source LW T67C from the company Osram, and the photodetector 8 a silicon photodiode S9032-02 from Hama-matsu photonics. In order for a device 1 according to the invention has been constructed using commercially available components and known methods, with the use of Bragg gratings as a filter of the wavelength-selective light emitting regions 12 neither etchings, nor other mechanical deformations of the optical waveguide 2 longer required.

Due to the novel structure of the fiber optic bending and position sensor device 1, the number of optical fibers 2 could be significantly reduced with the same functionality over known devices 1. This is accompanied by an advantageous reduction in the number of opto-electrical components, that is light sources 5 and photodetectors 8, as well as a reduction in the number of electrical and preferably via Plug connections performed optical connections to these opto-electrical devices in the example cases of six to only two achieved. This saves additional costs for secure connector systems. This results in a total of a fiber optic bending and position sensor device 1 with a compact structure that provides information about a value and a location of bending already using only one optical waveguide 2 based on POF, with all applications, as described, inter alia, in WO 94/29671 Al are known with such a device with improved quality and more compact design can be displayed.

Claims

claims 1. A fiber optic sensor device comprising an optical fiber (2) having a light source (5) coupled to a first end (3) and a light detector (8) coupled to the optical fiber (2) at a second end (7); and means for detecting a deformation based on a change in the intensity of the light source from the optical fiber (2) in the light detector (8), since it indicates that at the first end (3) the Optical fiber (2) light of several frequencies or wavelengths (λ _r , λ _b , λ _g ) is coupled, which is formed on the optical fiber (2) at a second end (7) coupled light detector (8) for frequency-selective intensity evaluation and the light emission regions (12) on the optical fiber (2) are designed to be selective in coordination with the frequencies or wavelengths (λ _r , λ _b , λ _g ) coupled to the first end (3). 2. Sensor device according to claim 1, characterized in that the light emission regions (12) are formed as Bragg gratings with wavelength-selective action. 3. Sensor device according to one of the two preceding claims, characterized in that a broadband emitting LED is provided as the light source (5). 4. Sensor device according to one of the preceding claims, since you rchgekennzeichnet that more than two different frequency selectively acting light emission regions (12) on the optical fiber (2) are provided, preferably three different frequency selectively acting light emission regions (12) per optical fiber (2). 5. Sensor device according to one of the preceding claims, characterized in that the optical fiber (2) is formed as a polymeric optical fiber (POF) which is provided with by direct writing with respect to at least one refractive index (n) manipulated light emission region (12). 6. Sensor device according to one of the preceding claims, characterized in that the light detector (8) is designed as a rbg sensor.