Method for identifying an object

A method of identifying an object

Introduction

The present invention relates to a method for identifying a objet.Etat art

Object of the Invention (Problem to be Solved by the Invention) The object of the present invention to provide a method of an object identifica¬tion. According to the invention, this object is achieved by someMethod according to claim 1.

General description of the claimed invention with principauxavantages.

A method of identifying an object according to the invention comprises the following éta¬pes: (a) illuminating at least one identification area on the surface of an object to re¬connaître with a coherent light and intercepting at least par¬tie a light reflected by the identification zone, so as to obtenirune interference pattern in etd'interception determined lighting conditions; (b) maintain this interference pattern as FIG dereferenced of interference of the object to be recognized; (c) placing a candidate object likely to be the object to be recognized dansles same lighting conditions and interception than utiliséespour get the reference interference pattern and get this objetcandidat an interference pattern; (d) comparing the reference interference figure with the figure of the candidate object interférencede; and (e) assessing the probability of identity between the object to be recognized and objetcandidat depending on the degree of correspondence between the reference figured'interférence and the interference pattern of the object candi¬dat.

The method of the invention uses an optical interference phenomenon, known as "speckle interferometry", for identifying an object objet.Lorsqu'un, which is not an ideal specular reflector is illuminated by unelumière coherent, microscopic variations on its surface dephase Lalumiere reflected and scattered. If it intercepts this light, for example on unécran, one can observe an interference pattern, or figure of "speckle" produced by interference between components of phase cettelumière. In the method according to the invention, an interference obtenuedans lighting conditions and interception is determined considéréecomme a unique fingerprint of the surface of the investigated object. Indeed, given lacomplexité the phenomenon involved, sensitive to surface variations WIDE micron, only the same object placed in the same conditionsdéterminées will produce a figure essentially identi¬que interference. Thus, according to the method of the invention, FIG interférenced'un object to be recognized is stored as a figure of réfé¬rence interference, unique fingerprint for identification. When it is desired by lasuite identify this object to be recognized from a plurality of items to be subject candidatssusceptibles to recognize, simply place each object candidatdans the same illumination and interception conditions as those used pourobtenir Figure reference interference and obtain the figure of interfé¬rence. A high degree of correspondence between a figure interférenceobtenue for a candidate object and the reference interference pattern permet¬tra to conclude with a high probability to the identity of the two objects, that is to say the candidate object is the object to be recognized. A first advantage beyond this method is its sensitivity, which makes it inviolable. Indeed, MyMethod is sensitive to variations in surfaces to micron scale, achieving a valid copy of the object to be recognized therefore being difficilementenvisageable. A second advantage of the method according to the invention does not require any marking estqu'elle, or treatment, of the object to recon¬naître. Indeed, preferably using state of natural surface àreconnaître object. Another advantage is that the identification of the object is directly sanscontact, which prevents wear of the identification area and delecture means of the surface, which here is a light beam.

Preferably, the coherent light source is a laser beam foca¬lisé on the identification area. One can use a traditional laser sources, eg HeNe type or a laser diode, the latter offering plusgrande flexibility.

The identification will advantageously have a surface area of ​​0.001 mm2 à0,1, preferably of the order of magnitude of 0.01 mm2.

Preferably, the identification area has a peak-to-roughness crêtesupérieure quarter of the wavelength of the laser. The identification area peutnotamment have a roughness peak-to-peak voltage of 0.15 to 0.20 μηι, which is the most caspour unpolished metallic surface. Deslasers can thus be used which radiate in the red.

The interception of the light reflected by the identification zone may simply sefaire by a screen. However, preference will intercept the lumièreréfléchie with a camera or a charge coupled device, which directly permetd'acquérir the interference pattern on computer means. CONSERVATION of the figure reference interference can therefore be done on computer unsupported. Furthermore, it is advantageous to determine the degréde match between the reference interference pattern and figured'interférence a candidate object using information support traite¬ment images, allowing greater objectivity.

Such an object identifying method may be advantageously dé¬veloppée to operate in access control systems, that is systems for triggering diredes similar action to a autorisa¬tion after checking the identity of an object introduced into the system. It can however also be used for identification of sensitive objects such as nuclear ducombustible. In this context, it has the advantage of being miseen work underwater.

Description using Figures Other features and characteristics of the invention will become apparent from detailed ladescription of an advantageous embodiment presented below, by way of illustration, with reference to the accompanying drawings. These show:

Fig.1: a diagram showing the reflection of light on a polished surface;

Fig.2: a diagram showing the reflection of light on a rough surface; Fig.3 is a diagram of an installation for the implementation of a preferred method of de-realization method of the invention;

Fig.4: a figure of Speckle.

The method of the invention utilizes a phenomenon opti¬ques interference, known as of speckle interferometry, for identificationd'objet. When a surface is illuminated by an optical beam, all pointsélémentaires this surface reflect incident light. Casd'une in the mirror-like surface, these points reflect in all mêmedirection as shown in Fig.1. In the case of a rough surface, whichis generally the case, the elementary points reflect in all lesdirections of space, it is called diffusion. If the incident beam estcohérent, the surface reflects and diffuses in all directions of the espacedes elementary beams which may interfere. By intercepting faisceauxélémentaires reflected on a screen, for example, one obtains a figure interfé¬rence or FIG Speckle, spots consisting of more or less lumineusescomme shown in Fig.3. Such a figure of interfer ence is sensitive to desvariations surfaces micron scale.

Thus, according to an important aspect of the invention, it is considered that figured'interférence produced by a surface portion given in conditionsd'éclairage and intercept determined is unique. Another portion desurface coming from the same object or a different object in the same conditions gives a figure of different interference. Such figure interfé¬rence thus constitutes a unique fingerprint of a surface and can be utiliséepour identify an object.

It is based on this observation has been developed méthoded'identification the object of the invention. In Figure 3 is shown a schémad'un assembly allowing the implementation of a preferred embodiment decette method. Reference 10 indicates a laser source that is a diode laserLepton II (Micro Laser System) for emitting a beam lumièrecohérente 6 mm in diameter and negligible divergence. Delumière the beam from the laser diode is reflected on a separator 12 in the direction of anObject target 14. As explained, the incident light beam is reflected by etdiffusé the surface of the target object 14. A camera 16 makes it possible to intercepterune part of the light reflected by the surface of the target object 14 so ofobtaining an interference pattern. A lens 18 of the type "planoconvex" montéeentre the target object 14 and the separator 12, focuses the incident beam onto the target lasurface 14 and serves for the collection of the diaphragm faisceauréfléchi by the surface of the target object 14. A filter 20, placed in front of the camera 16and passing only light of the same wavelength as the laser 10, overcomes the ambient light conditions. 12réalise the separator separating the light reflected by the target object of faisceauincident. Its orientation is such that parasitic reflections will formentpas on the camera sensor 16. The use of a computer 16 connected toa camera allows for the direct acquisition of the figures interfé¬rence, and retain in the form of computer file. Moreover, the figures ana¬lyse interference can be objectively using delogiciels data processing.

In a first step (a) of the method according to the invention, the object of the cible14 Fig.3 is an object to be recognized. Positioning the object to a predetermined position reconnaîtredans, defined for example by studs of position¬nement. This is followed by the acquisition of an interference pattern of a zoned'identification the object to be recognized in the lighting conditions etd'interception of the reflected light determined, which is stored. The interference pattern is then stored (step (b)) in the computer as reference figured'interférence of the object to be recognized. This méthodepermet subsequently identify the object to be recognized among other objets.Ainsi, in accordance with step (c) placing a candidate object likely to êtrel'objet to recognize in the same position, ensuring the same conditionsd'éclairage and interception as those used to obtain the figure of interfé¬rence reference conditions of step (a). The interference obtenueest then compared (step d) to the reference interference figure of the dulogiciel using image processing. Is thus determined a degree of correspondanceentre the interference pattern and the reference interference figure, to partirduquel one can evaluate the probability of identity between the object to be recognized etl'objet candidate.

The identification of the object area to be recognized may have a small superficietrès, of the order of 0.01 mm2. To observe the phenomenon of interfé¬rence, the identification area should preferably desurface variation of height, peak-to-peak, higher than the quarter of the length of laser ondedu. We are talking here of Rt roughness (peak-to-peak) and not the ACSD roughness Ra. For example, the roughness may have a value of environ0,16 μηη when working with a red laser at 0.633 μίτι.

Note that the optical system, that is to say the provision of dumontage Fig.3, and the laser intensity parameters are the plusimportants when obtaining an interference pattern. Therefore STEP (c), reproduces the same lighting conditions (laser intensity) etd'interception (same provision of mounting) as in step (a). If these conditionssont respected and that the current candidate object is the object to be recognized, onobtiendra a figure substantially identical to the figure of interference interfé¬rence reference, subject of course that surfaceobservée portion is the same that in step (a). It is therefore important to bienpositionner the candidate object under the assembly of Fig.3. For example, when using rectangular objects of equal height may be provided with object unsupported positioning pins disposed at right angles. Oncalera then all samples in the same manner against the pads, allowing an excellent positioning reproducibility. Thus, if the current objetcandidat is the object to be recognized, the incident beam trouveraautomatiquement on the identification area.