WO1988001080A1 - Assembly of elements for the remote reading of identification marks on a substrate - Google Patents

Abstract

Assembly comprising a coded substrate which may be read from a distance (several metres) by a scanning device comprising a beam oscillating in a given sector and a coupled analyzer for the reflected light. The substrate comprises back-reflecting areas of substantially equal intensity, the difference between them being related to the chromatic content of the reflected light or, the latter being circularly polarized, to the direction of said polarization. In another case, certain coded areas diffuse the light along a conical divergent beam, other areas sending back the reflected signal in a direction substantially parallel to that of the incident beam. Application to a transceiver system (44) arranged on board a vehicle for reading road signs. It comprises a light source (55), a first semi-reflecting blade (56), an objective (57) intended to form a thin vertical light beam. While running, the vehicle causes the scanning of a back-reflecting surface (53) capable of changing the polarization of the incident light and carrying a coded signalling indication. A second semi-reflecting blade (58) is arranged in the path of the back-reflected beam and directs said beam onto two polarizing analyzers (59, 60) associated with two respective polarization sensors (61, 62) forming signals (A, B) sent to an AND gate (63) and to an interpretation unit (65) which sends the decoded indication to a display (66).

Description

 ARRANGEMENT OF ELEMENTS FOR REMOTE READING OF IDENTIFICATION MARKS ON A SUBSTRATE

The present invention relates to the remote reading of images and, in particular, the remote identification by optical means of marks and control drawings that a substrate comprises, in particular a label in the form of a sheet, film or other wafer or card in the form of laminate.

There are already distinctive marks affixed to objects (goods, vehicles, machinery control bodies) which must be read at greater or lesser distance for the purpose of identification and control; such are, for example, the "bar codes" appearing on articles sold in supermarkets, these codes being read by a device installed at the cash register and making it possible to automate billing operations.

The document TECHNISCHE RUNDSCHAU 11/86, p. 63, describes the remote identification of highway stickers affixed to vehicles. According to this document, such an identical ^'fication can be done by radar, the label having in its thickness a reflector circuit micrometer waves. According to another embodiment, the label includes a mark or a drawing consisting of retroreflective areas of light (visible or IR), the reading device (placed on the deck of a bridge spanning the road) consisting of an excitation laser and a device and detector, point by point, of the reflected light, laser and detector being coupled to a scanning mechanism exploring a given solid angle.

The document GB-A-2,106,832 (STANDARD TELEPHONE & CABLE) describes the reading of transparent cards comprising marks modifying the transmission, the reflection or the polariza¬ tion of light in the areas where they are printed. The reading of such cards (for example prepaid cards) can be done using one or the other of the aforementioned effects or, for more security, a combination of these.

Document GB-A-2,125,539 (STANDARD TELEPHONE & CABLE) describes a process for remote reading of a reflective element tor, comprising the projection onto this element of a visible or invisible light signal and the detection of the corresponding reflected signal, the content of this reflected signal being able to correspond to the incident signal or to a modification thereof. According to one embodiment, certain zones of the reflecting element linearly polarize the incident light and reflect it in a given plane (for example horizontal) while certain other zones operate inversely, which makes it possible to distinguish them from one another. remotely.

Document DE-A-3,030,769 (HEBERTS GESELL) describes a plate or sticker intended for vehicles comprising a retroreflective intermediate layer and an external layer codable by pressure. The coding operation unmasks, in the appropriate zones, the intermediate layer and the coded mark becomes visible in certain circumstances by retro-reflection.

Although the techniques proposed in the prior art are interesting, they are not exempt from certain drawbacks, the main ones of which concern security against decryption, reliability of reading and convenience of printing the code.

Indeed, it is obvious that systems based on the technique of "all or nothing", that is to say production of a given signal, for example by certain zones (A) of a plate or of a label, the rest of it (zone B) providing no signal (or a signal weakened in intensity), are capable of being identified relatively easily and then copied; moreover, the contrast between zones A and B (especially for labels subject to weathering and handling) risks weakening over time and the mark may become illegible by detection devices. Finally, the previous documents relate, for the most part, to techniques of remote reading of a very limited number of states (for example "on" or "off") or else, the presence or absence of a unique distinctive area.

In the present invention, an attempt is made to make available a set of elements allowing remote reading; this set includes an information-carrying substrate, readable from a distance, in the form of retro-reflective areas of its surface, a source of radiant energy, in particular of visible or invisible light, providing a beam of incident light intended to scan or simply illuminate the substrate carrying the information and a sensor device / - reader of the energy signals retroreflected by said areas, these having, juxtaposed, at least two zones A and B, distinct, of defined optical properties, provided after the reflected signals have been detected and read by said sensor, electrical signals making it possible to translate and finally to display by electronic processing the content of the information stored by said substrate. In one embodiment, a remotely readable label or mark is provided, the code of which can be entered by simple means (possibly even by hand) and, by its possible complexity, having a high degree of coding versatility , security and reliability. A typical example of such a distinctive mark is constituted by a personal badge codable to order and distributed to the members of a company. The coding of the badge entrusted to certain privileged persons is read remotely so as to give them access (for example by automatic opening of doors) to certain protected places; such a badge can be coded just before use, if desired, and can have a completely individual characteristic, for example in the manner of a security key with respect to its lock.

Furthermore, the code of such a badge must, preferably, be invisible to the eye so as not to be detected and resist analysis by current means so that it cannot be counterfeited during the (limited) period during which it remains in effect. Thus, one of the objects of the invention is a label or badge in the form of a sheet, film, wafer or any other laminar or laminated article which can be affixed to an object, a vehicle or carried by a person and comprising, on its surface, a series of reflective areas arranged so as to constitute a design or mark (preferably invisible to the eye) which can be identified remotely by a scanning reading device. A label whose parameters correspond to those of the substrate described in the assembly defined in claim 1 meets such criteria. In general, zone A of the label reflects a signal of a first type and zone B reflects a signal of a second type different from the first, it being understood that, during this process, no attenuation occurs notable energy retransmitted. For simplicity, it will be said hereinafter that the surface A reflects a signal A and that the area B reflects a signal B, the signals A and B being of practically constant and similar intensity. Zone A may for example correspond to an inscription on a surface B, the signal A possibly having, according to a first embodiment (I), a chroma¬ tick content different from that of the signal B. Thus, the coating of the area a can be composed of a re léchissant system substantially a wavelength λ, while the area B may include a system reflecting a different wavelength ^λ B ^_"λ a ^e ^ ^λ BP ^EUVE nt part beaches visible, UV and IR.

The content of the incident excitation signal may contain only λ ^ and λn or may be more complex, taking into account that, then, the coating of zones A and B is provided to absorb and retain non-useful radiation.

In another embodiment (II) involving an incident polarized signal, the zones A and B can be distinguished by the change (or non-change) in the state of polarization that they are likely to impart to the reflected light, for example the zone A can reverse the direction of rotation of the circularly polarized light while B does not introduce any modification of this direction.

The international search report provided the following documents: Document GB-A-1,314,002 describes a technique for the remote recognition of retroreflective marks affixed to objects, this technique implementing a scanning system. The main object of this docu¬ ment is a device (and its variants) for scanning and reading. The brands to be recognized do not have any special characteristics (apart from their reflective property of the light) .

Document US-A-, 544,836 describes coded cards with optical reading. These cards include marks made up of adjacent zones of distinct polarizing properties (see FIGS. 6A and 6B) the aim of which is to provide, by reflection, detectable signals with distinct optical properties. This document does not however indicate that the intensity of the light reflected by said adjacent areas is equal or similar and, moreover, this document does not deal with the problem of remote reading like the present invention.

Document US-A-4,175,775 describes a personal identification card comprising, inserted between a retroflective material and an opaque optical filter with visible radiation, the portrait of the user in the form of a slide. Reading is done in IR or UV by means of a video detector.

Document CH-A-589,326 discloses a device which seems particularly suitable for reading current bar codes. It describes a retroreflective label (see Fig. 6) having, interposed between a metal-area ^"Lisée and the screen (10) itself incorporating the distinctive marks, a blend of glass beads or other maté¬ riau retroreflective.

Document US-A-, 085,314 describes an encodable retroreflective laminar material making it possible to manufacture, by decou¬ page, identification cards. This material comprises a retroreflective base covered with an opaque self-adhesive film which can be detached in portions, so as to thus produce detectable marks on its surface according to a chosen design.

We will see later how one realizes practically the cases I and II above-mentioned. It will be noted that, in the present invention, it is also possible to envisage other optical modifications, in particular, if the light is coherent, a phase or coherence modification introduced by one or other of the zones A and B, but this without noticeable weakening of the retransmitted energy. It is also possible to introduce modifications in the direction of the signal reflected by the coded zones A and B which are not coded. For example zones B, not coded, reflect the signal in a direction substantially parallel to the incident ray while the zones B, coded, reflect this signal in a divergent manner, for example in the form of a conical beam.

The following drawing illustrates the invention.

Fig. 1 is a schematic section of a label according to the invention.

Fig. 2 shows a variant.

Fig. 3 is a schematic representation in perspective of a device according to the invention showing the lighting and scanning elements of the label.

Fig. 4 shows a detail of FIG. 3. on an enlarged scale.

Fig. 5 schematically shows, in horizontal section, another embodiment of the label of the invention and the corresponding reading device.

Fig. 6. is a diagram of another embodiment of this erisemble.

Fig. 7 shows diagrams of the received and ^" decoded signals.

The label 1 (see fig. 1 to 4) comprises a base support 2 on which, in a linear configuration 3, a series of retro-reflective elements 4, cube or glass cube corners or choriant retroreflective beads with a high refractive index, for example made of titanium glass or any other known retroreflective element (see for example document US-A-4,036,552); it will be recalled that the main characteristic of these retroreflective elements is to return the reflected signal in a direction practically parallel to that of the incident beam. In the drawing, for reasons of simplicity, only one strip (3) of these elements has been shown; it is understood that there could be several of them, the reading device then necessitating scanning on several levels, for example by means of a television camera which implies remote reading means more complicated and expensive than that, relatively simple, shown in Figure 3. Covering the retroreflective elements, this label includes still a layer 5 of material "codable", that is to say of a material 6 which may be given locally the Proprie ^¬ tee to change the nature of light reflected by the elements 4. The coded areas are represented in the drawing by the number 7.

Such a material can be: for example, a thermochromic or piezo-chro ic substance, that is to say a substance whose absorption band can be moved (in the wavelength range) by heat or pressure. Thus, if the material 6 transparent to radiation λ »is heated locally so that it becomes transparent, no longer at λ _A , but at a different wavelength λ _β and that it is illuminated (I) by an incident signal containing λ, and λ _β (for example in approximately equal proportions), the light reflected by the label 1 will include a portion λ _{R re-} emitted by the portions 6 of the layer 5 not coded (zone B) and a portion λ ^ reflected by portions 7 (zone A) coded.

The remote reading device (fig. 3) comprises at least one source 11, for example a laser 'providing a ^" coherent visible monochromatic signal or IR, or any other source emitting a signal of selected composition, for example λ ^ and λ _β , a separating blade or prism 12, a plane-cylindrical len¬ tille 13 and, oriented so as to receive, deflected by the separating element 12, the light reflected by the card 1, a detector 14. The light emitted by the source 11 is converted into a vertical plane beam 15 by the cylindrical lens 13, this beam being projected at an angle of exploration suitable for the label 1 (for example in the form of a badge worn on the buttonhole of a person) comes to intercept a portion of it. The beam 15 is animated with a lateral scanning movement (by means of a traditional system to which the organs of the present device are coupled but which is not represent é in the drawing so as not to make it heavier), of sufficient amplitude for the wearer of the badge to be within his field of action regardless of his position (in a given sector of course). The scanning frequency must be high enough to avoid errors due to the wearer's own movement badge, for example of the order of 10-100 Hz.

The detector 14 is a conventional member known to those skilled in the art, for example a spectroscopic analyzer with photoelectric detector, and capable of differentiating the wavelengths λ ^ and λ ₂ as a function of the scanning position and therefore of supply a modulated signal corresponding to the geometric arrangement of zones A and B along strip 3 of the label. This signal is then amplified, processed by conventional circuits and compared with stored data in order to control a device intended, for example, to trigger an alarm or to open a door.

The variant of fig. 2 differs from that of FIG. 1 by the presence of a layer 21, also programmable, but according to another principle. In this case, the source 11 is constituted by a circularly polarized light emitter by the usual means (linear polarizer, then Babinet compensator, for example) and the layer 21 comprises a birefringent material of a suitable thickness for consti ¬ kill a "λ / 4 plate" (a polymer film oriented by stretching, for example) whose retarding property on the transmission of one of the vectors making up polarized light can be canceled locally in an irreversible manner (coding) for example by heat e / or pressure. The non-active coded zones (A) are indicated by the number 22, the active zones (B) are marked 23. The corners of cubes 4 are coated mirror-like (for example on the The incident light I circularly polarized (for example, on the right, D) and striking the active non-coded zones 23 undergoes the following changes of states: a) passage through the retarding film = linearization; b) reflection by the faces of the cube (3 successive reflections) = conservation of the linear polarization; c) new passage through the film λ / 4 = circular polarization, (D). As far as the A 22 coded areas are concerned, the changes are schematically as follows: a) no effect; b ⁾ three successive reflections = inversion of the state of circular polarization (G); c) no effect. The rotation of the light reflected by the zones 22 will therefore be the reverse of that reflected by the zones 23. These differences are detected easily by conventional devices known for the detection and analysis of circularly polarized light and no confusion is possible even in the case of very low light intensity, which explains the reliability of the system of the invention, even at relatively large distance of several tens of meters. It should be noted that it is also possible to use, as retroreflective elements, corners of uncoated cubes, the reflection on the faces then being done by total reflection. The retarding effect of the retro-reflective element: Ichissant being, in this case, equivalent to a bireflective element of optical thickness λ / x, a birefringent compensating film is then inserted between this element of the coding layer 21.

According to another embodiment III of this label, this comprises, as codable layer (in place of layers 5 and 21 of FIGS. 1 and 2), a transparent film which can be made opalescent, during coding , by heat and / or pressure. Such films, made of plastic, are found commercially; they are manufactured by laminating a sheet of thermoformable material between rollers, at least one of which is frosted so that the surface of the sheet becomes opalescent and diffuses the light at a certain solid angle. Then, by another rolling between smooth surfaces, its transparency is restored to the sheet, the opalescence however remaining underlying and can be restored locally by heating. Such local heating is of course, in the present case, the desired coding of the present label. Such sheets are described in US-A-4,163,570.

It will be noted in passing that a similar effect could be obtained in the absence of a codable layer proper, that is to say by simply using, on a base layer, a retroreflective layer of the "REFLEXITE" type comprising cube corners printed by stamping in a plastic sheet, and, to carry out the coding, by locally deforming them so as to modify their optical properties so that instead of reflecting the signal parallel to the incident ray in the direction of the source they broadcast this signal in a given solid angle.

Fig. 5 illustrates a device for scanning and reading a label, the coded areas of which reflect reflective light at a certain angle relative to the direction of the signal reflected by the non-coded areas.

Such a label comprises a support layer 30, a retroreflective layer 31 and a codable layer 32 comprising transparent zones 32 B and zones diffusing the reflected light 32 A in a cone limited by the arrows 33.

The scanning reading device, similar in broad outline to that shown in FIG. 3, comprises: an incident light source 34 emitting a scanning signal 35 concentrated by a cylindrical lens 36 in the form of a vertical beam 37 projected against the label to be decoded. A semi-mirror 38 is inserted in the path of the beam 35 so as to deflect, towards a detector 39, the signal reflected by the label when reading non-coded areas, this signal being practically superimposed on the beam incident 35, 37.

The device also comprises a mirror 40 pierced approxi¬ matively in its center to give passage to signal 35 and making it possible to deflect, in the direction of a second detector 41, the signal 33 broadcast by the coded areas 32 A of the label, this signal being concentrated through lens 36.

The operation of this device is therefore obvious from the foregoing, taking into account the fact that the lens 36, by a reciprocating movement not shown, makes it possible to explore _r by scanning, the sector in which it is placed. the label. As regards the other elements of this device (not shown), they are similar to those ensuring the operation of the device of FIG. 3.

As irreversible thermochromic substances, cobalt-based compounds can be mentioned (DE-A-2,515,474; RAYCHEM; Bull. Chenu Soc. Japan 49. (1976), 1563-67; CH-A-581.871; 592.927; 598.661). Mention may also be made of heavy metal sulfides. A combination of 2- ⁽ 2-ethoxyethyl ⁾ amlno-3-chloro-6- (diethylamino) -fluorene corn can also be used. precursor dye and bisphenol A in polyvinyl alcohol as a binder (see US-A-2,663,654 to 2,663,657; US-A-2,740,895 and US-A-2,746,675). It is also possible to use condensation products between ammonium salts of indole and of benzothiazole with salicylaldehyde and its derivatives (RC GUGLIELMETTI et al., Ist International Congress on Advances in Non Impact Printing Technologies (1981), June 22-26, Venice, Italy.

As regards the variant of FIG. 2, it will be noted that- λ / 4 wave plates can be made of conventional birefringent materials such as quartz, mica, calcite cut appropriately so that the thickness is adapted to cause the phase differences required for the wavelengths used.

Furthermore, many plastics may also be suitable, in particular polyvinyl alcohol, mylar, stretched nylon (which have 'birefringen¬ tes' properties). It is also possible to use celulose acetate butyrate as well as cellulose nitrate, the retarding effect of which depends on the wavelength, which makes it possible to produce an achromatic compensator for white light. Certain types of cellophane may also be suitable. A series of references on this subject can be found below: NA SHURCLIFF, Polarized Light, Production and Use, Ha ard Univ. Press, Lambridge Mass. (1962), p. 99-101; CD. WEST et al., J. Opt. Soc. Bitter. 29 _. (1949), 791; EF FAHY et al., NATURE 17d (1956), 1072; E. HECHT & A. ZAJAC, Optics, Addison-Wesley, Reading 1979, p. 246-251; J. Phys Chem. 34. (1930), 165; USA 2,018,963; US-A-2,099,694. To carry out the coding, signs can be printed by means of a heated matrix, the various signs to be printed being chosen and arranged according to a pre-established code. One can also, in certain cases, print these signs manually by means of a stylus with a heated point of conventional type (soldering iron type).

The following examples illustrate the invention.

Example 1

We used a 0.76mm thick PVC card, credit card format. A sheet of REFLEXITE type retroreflective material (Reflexite Corp., New Britain 06051, Conn. USA) was bonded to this card, using a standard adhesive, then an adhesive PVC stretch film.

By means of a pyrography pen, marks on the outer layer of the card, and along a fictitious horizontal line, were marks in the form of vertical bars of different thickness and irregularly spaced, this arrangement of the marks being predetermined.

The card was then presented to a scanning device as described above comprising a He-Ne laser whose beam, linearly polarized at 45 °, was dispersed by a plan-cylindrical lens over a vertical angle of 15 °: the lens itself was driven back and forth 10 Hz horizontally, causing the beam to sweep an angle of about 35-40 °.

The light reflected by the card was collected by a diode detector coupled to the lens and the signals supplied by the detector were taken up, analyzed, processed and stored electronically by a polarization analyzer, and an amplifier-microprocessor of types usual.

For remote identification purposes, the card was then placed at a distance of approximately 1 m from the above reader and subjected to a series of linear horizontal and vertical movements, of rotations around a perpendicular axis. ¬ circular to its plane and oscillations around a transver¬ sal axis, the coded side remaining, of course, in the field of observation of the reader. It was found that the information read by it was identical whatever the movements and the position of the card, within the limits indicated. Note the considerable advantages that this implementation of the invention provides in relation to known devices, in particular that described in document GB-A-2 125 539; in fact, in the latter, the angular position of the probe relative to the reader cannot be arbitrary, an angle of 90 ° between the direction of polarization of the reflected signal and the orientation of the polaroid filter interposed on the passage of this signal being necessary to produce the extin- tion of this signal. In the present embodiment involving a circularly polarized response, the angular position of the card can be arbitrary. Furthermore, the coding described in this example is invisible to the naked eye.

Example 2

A card similar to that of Example 1 was used, successively covered with a layer of approximately 100 μm of nickel chloride / hexamethylene tetrammine decahydrate (see Bull. Chem. Soc. Japan 49. (1976), 1563-67). finely crystallized (obtained by air drying a layer of aqueous solution deposited on the surface of the card) and a layer of PVC of approximately 50 μm obtained by spraying using a solution of PVC in chloroform.

The source of the reader consisted of an IR beam (by diodes) comprising mainly radiation at 20,000 crn ^" (absorption of the decahydrate above) and 25,000 cm ^-1 (absorption of the above salt in the dehydrated state ).

The coding was entered using a pyrography pen, the heat of which had the effect of dehydrating the decahydrate in the affected areas and providing zones whose maximum absorption is displaced by 5000 cm-- ' - compared to the rest of the map.

The reading device conforms to the description given above, with the exception of the detector which comprises elements selectively sensitive (by appropriate filtering) to radiation at 20,000 and 25,000 cm ^-1 .

The behavior of the above card as well as the results obtained are substantially the same as in the case of Example 1.

It will be noted that in another embodiment of the present assembly, the light source and the reader are installed on a road vehicle while the substrate consists of an indicator panel. The purpose of such an arrangement is to provide the driver of the vehicle with the information affixed to the panel in a more legible manner and for a longer time than that simply corresponding to the passage of said vehicle opposite said panel. Thus, this embodiment relates to an assembly comprising a fixed substrate carrying information with retroreflective properties, a mobile light source for directing a beam of light towards this substrate and a receiver also mobile with retroreflected light.

Various solutions have already been proposed for reading information remotely between two points which are animated by a relative displacement. Thus, for example, EP-A2-0,062,473 relates to the remote reading of car license plates made of a retro-reflective material, that is to say a material endowed with optical properties which allow it to reflect the incident light parallel to itself. This solution is based on the measurement of the intensity of the light received by the receiver. The problem to be solved is in particular to establish a distinction between light coming from diffuse or specular reflection coming from another light source illuminating the area observed. Based on the light intensity of the retroreflected light, this solution is extremely vulnerable to the state of cleanliness of the information medium. However, in the case of a license plate, the information medium is precisely likely to be more or less clean and therefore exert an influence which can be preponderant on that of the information itself making it inde¬ encryptable. This is obviously a major drawback, since the information must be able to be perceived in all circumstances.

This drawback is found in the solution proposed by DE-A1-3,509,965 which describes a well-known code bar system registered on the road and detectable by a receiver of the light reflected from an incident beam coming from a light source secured to the vehicle which also carries the receiver. The non-use of retro-reflection in this case does not make it possible to read from a distance, hence the idea of putting information on the road, which poses even more complex problems both in terms of information only from the transceiver device to be placed under the car. Such a solution is envisaged for transmitting the FM frequency bands for radio Reception ^¬ tors placed on board of vehicles.

It is certain that in the current traffic, there is a quantity of information intended for the drivers of the vehicles, in the form of road signs, of indications of directions in particular that it is very difficult to memorize and to update constantly. This is how it happens to each driver that he no longer knows what is the speed limit authorized on the stretch of road he is taking, whether the overtaking is aurotized or not etc. When entering a tunnel, he may forget to turn on his lights or turn them off when leaving. He may also forget or not have time to memorize directions.

This is the reason why a system for transmitting coded information, for displaying and for constantly updating this information on board a road vehicle, is of real interest, the driver being able to constantly check when necessary. if 'its speed is adapted to the regulations, or if it is or is not authorized to exceed without risk of violating these regulations. Other information such as the automatic switching on and off of the headlights at the entrances and exits of tunnels could also be used to act directly on the electric power supply circuit of the headlights to control the switching on and off. . The same could be done on radio receivers to adapt the FM frequency band to the location in which the vehicle is located.

For such a system to be of real interest, it is obviously necessary that the information can be perceived with great security, which supposes that it does not have the drawbacks of the above-mentioned solutions.

This is the purpose of the assembly according to the definition of claims 1 and 21.

The essential advantage of this variant is that the reading of the information results from the fact that the modifications made to the light reflected by the different areas does not affect the intensity of the light and that the characteristics thus modified are therefore not dependent on a quantitative parameter whose value is likely to be affected by all kinds of environmental factors (state of cleanliness, visibility, ambient light).

It is obvious that such coded information is much less vulnerable to the environment than what has been proposed so far. In addition, taking into account the fact that the emitter and the light receiver are mounted on the vehicle by directing the beam axis at a certain angle with the rolling direction of the vehicle, if this beam is formed by a brush lengthened vertically, the necessary scanning of the information carrier results from the movement of the vehicle, so that the apparatus can remain entirely stationary relative to the vehicle, which simplifies its execution.

FIG. 6 represents a road traffic sign 51 which, in addition to the conventional signage 52 readable by road users and communicating prohibitions, obligations ^" , warnings and indications, linked to the traffic code, comprises coded information 53 which corresponds to that of the signal 52, - but is intended to be read using "a device placed on board a vehicle. The coded information 53 consists of a track made of a retroreflective material which has the additional property of modifying an optical property of the incident light. Such a material is described above in detail. In the example described here, the retroreflective coded information 53 is formed by a succession of two kinds of areas which polarize the incident light sometimes to the left, sometimes to the right, defining an alternating succession of states 0 and 1.

The device placed on board the vehicle comprises a transceiver 54 comprising a light source 55 formed by a laser diode, a first semi-reflective blade 56, a lens 57 intended to form a thin light beam oriented substantially vertically, a second semi-reflecting plate 58 disposed in the path of the reflected light beam and which simultaneously directs this beam on two polarization analyzers 59 and 60 associated with two respective polarization detectors 61 and 62 detecting respectively the polarization at right and left and forming the signals A respectively B which are illustrated in FIG. 2.

The signal A is sent to an "AND" gate 63 and the signal B is sent to this same gate 63 via an inversion gate 64. The gate 63 produces a resulting signal A '= A * B which is also represented by the diagram in fig. 7.

The decoded signal A 'is then transmitted to an interpretation unit 65 which, depending on the nature of the message directs it "to its destination which may for example be a display 66 when it is a question of inform the driver of the maximum authorized speed on the road section he is taking or other instructions such as the prohibition to overtake or even both simultaneously. The message can also be of another kind and carry out a function in place of the driver by actuating a relay 67 to switch on, for example, the searchlights at the entrance to a tunnel and turn them off at the exit, this last command being neutralized in the event that the searchlights were already turned on before enter the tunnel for example at night or in rain or fog. One can also imagine other functions symbolized by unit 68 which may relate to direction indications or to the automatic adjustment of receivers FM radio.

Regarding the scanning speed which is defined by the vehicle speed and is therefore variable, there are different means, for example, the start of the coded signal can give a time base which is used to decode the rest of the signal constituting the information itself. Special known algorithms can also be used, such as those used for reading magnetic cards intended to be inserted manually in a reading device and for which the insertion speed is also variable.

As has already been pointed out previously, the change in phase of the flexed retrored light is only one form of execution of the invention. It is possible to use other light modifications, such as changing the wavelength. Whichever solution is adopted, the signal sultant A 'is always the result of two signals A and B which are very little dependent on the Intensity. Thanks to this particularity, the detection of the coded track is independent of ambient light. Below a certain limit distance from which the coded track is detectable by the transceiver, the distance no longer has any influence on the detected signal. The same applies to the influence of dust or rain on the coded track. As long as this track is not covered with a layer perfectly opaque to the incident light beam, its detection is possible without appreciably affecting the signal to noise ratio, unlike what happens with all remote reading systems based on a variation in intensity.

This high reliability in detection makes it possible to use simple and inexpensive apparatus which are important conditions in a field of as wide distribution as that of the automobile. •

Claims

1. Assembly comprising a substrate carrying information, readable from a distance, in the form of retro-reflective surface areas, a light source providing a beam of incident light intended to scan this substrate and a sensor / reader of the light signals retroreflected by said said tracks, these having, juxtaposed, at least two zones A and B of distinct optical characteristics providing, after reflection and detection of said light signals by said reader, corresponding electrical signals making it possible to translate and display, by processing electronic, the content of the information stored by said substrate, characterized in that the light signals reflected by zones A and B are optically differentiated from one another by properties other than their intensity, the latter being practically equal for the signals reflected by the two zones. 2. Assembly according to claim 1, characterized in that at least one of the zones A and B modifies in a detectable manner, during the reflection by its surface of the incident light, the optical properties thereof. 3. An assembly according to claim 2, characterized in that the zone A modifies by filtering the chroma¬ tick content of the signal reflected by this zone. 4. The assembly of claim 2, wherein the substrate is subjected to scanning by a circularly polarized light beam, characterized in that its surface modifies, by reflecting it, the state of polarization of this light beam. 5. The assembly of claim 1, wherein the substrate is subjected to a scanning by coherent incident light, characterized in that the zone A causes a phase change of the reflected light. 6. The assembly of claim 1, wherein the substrate is subjected to scanning by a beam of coherent light, characterized in that the area A causes a change in coherence of the beam of reflected light. 7 »An assembly according to claim 1, characterized in that the area A of the substrate differs from the area B by the solid angle in which the corresponding signal is reflected by one and the other area. 8. The assembly of claim 3, wherein the substrate is subjected to a scanning by an incident light containing at least two components λ, and λ _R of different wavelengths, characterized in that the zone A mainly reflects the component λ, while the area B mainly reflects λ _R. 9. An assembly according to claim 4, characterized in that the zone A reflects a light signal circularly polarized to the right and the zone B reflects a signal polarized circularly to the left, or the reverse. 10. The assembly of claim 1, characterized in that the substrate consists of a plate or label and that it comprises, successively laminated, a layer of base plastic, a retroreflective layer formed of beads of transparent material with a high refractive index or of cube corners, then either a layer of piezo -or thermochromic material, or a λ / 4 film of piezo-or thermosensitive stretched poly¬ mother whose optical axis is in the plane of the film _r is also a transparent film which can be made subsequently opalescent and, optionally, a protective layer optically inert to coding. 11. Assembly according to claim 10, characterized in that the surface material of zone A of the label results from a local modification, in particular by the application of heat and / or pressure, of the coating of zone B. 12. An assembly according to claim 1, characterized in that, in addition to a source of radiant energy and means for forming this energy in a beam, it comprises means for scanning with this beam a sector of given space and that the means detection and reading are coupled to the scanning means and arranged so as to analyze the optical structure of the retroreflected light as a function of the geometrical arrangement, on the label, of the retroreflective zones- xion. 13. The assembly of claim 12, characterized in that the radiation energy is UV light, visible or IR, coherent or not. 14. The assembly of claim 13, characterized in that the light is coherent and that it has a longitudinal coherence at least equal to the distance of lec¬ ture. 15. The assembly of claim 13, characterized in that this light is polarized. 16. The assembly of claim 13, characterized in that this light essentially comprises two distinct wavelengths λ, and λ _R. 17. The assembly of claim 13, characterized in that said source comprises at least one of the following elements: a flash or incandescent lamp provided with appropriate filters, a laser, a light emitting diode, a laser diode. J.8. Assembly according to claim 12, characterized by 1 = fact that the means for forming the beam light and scanning comprise a cylindrical lens transforming the light from the source into a linear beam. 19. The assembly of claim 12, characterized in that the means for forming the beam light and scanning comprise an oscillating mechanism imparting to said beam a back and forth movement. 20. The assembly of claim 12, characterized in that the means for detecting the retroreflected light and for analyzing its optical content comprise, as required, a photovoltaic spectrophotometer, a polarization state analyzer, a phase analyzer or a coherence analyzer or a solid angle analyzer of the scattering. 21. The assembly of claim 1, characterized in that the light source and the reader are arranged on a road vehicle, the axis of the beam from this source forming a certain angle with the rolling direction of the vehicle, the substrate being arranged in the path described by said light beam following the displacement of this vehicle.