METHOD FOR MEASUREMENT OF DISTANCE OF OPTOELECTRONIC TYPE AND DEVICES FOR THE IMPLEMENTATION OF SAID METHOD

Abstract: It is described a method and relating device for measuring a distance from a surface, using three optical radiation transmission or reception channels, having a given emission and respectively reception divergence angle, said reception channel(s) collecting the optical radiation rediffused by said surface toward which it is emitted by said transmission channel(s). The transmission and reception channels are placed substantially at the same distance for said surface, with parallel optical axes, and the distances between the optical axes of said transmission channel(s) with respect to said reception channel(s) are different and preferably coplanar.

Description: DESCRIPTION "Method for measurement of distance of optoelectronic type and devices for the implementation of said method" TEXT OF THE DESCRIPTION The invention relates to a method and relating device of optoelectronic type for measurement of distance, specifically the distance between the measuring device, or a part of it, and a given surface, that is based on the transmission and reception of optical radiation fluxes towards and from said surface respectively Optoelectronic devices for the measurement of distance comprising a transmission channel and a reception channel are already known in the art In said known devices the transmission channel emits a radiating flux towards a surface the distance of which is to be measured, a portion of flux is rediffused by the surface and collected by the reception channel Assuming the optical characteristics of the two channels, their position and the reflectivity characteristics of the surface remain constant, the flux amount collected by the receiver depends only upon the distance value So the distance can be calculated by measurement of the flux amount received The main drawback of this measurement method is the need to know in advance the reflectivity characteristics of the surface, because of the sensitivity of the measure to the reflectivity characteristics of the surface The object of the invention is to overcome the above drawbacks and allow the implementation of distance measuring devices, which are of inexpensive construction and easily manufactured, as well as miniatuπzable, and which preferably give the possibility to achieve a good insensitivity to the reflectivity characteristics of the surface whose distance is to be measured. The invention achieves the above objects by a method for measuring a distance from a surface, characterized in that three optical radiation transmission or reception channels are used, having a given emission or respectively reception divergence angle, said receiving channel(s) collecting the optical radiation rediffused by said surface towards which it is emitted by said transmission channel(s), and in that said transmitting channel(s) and receiving channel(s) are placed substantially at the same distance from said surface, with parallel optical axes, and the distances between the optical axes of said transmission channel(s) with respect to said receiving channel(s) are different In a first type of embodiments the three optical radiation channels comprise one transmission channel and two reception channels, as in the claims 2 to 6 In a second type of embodiments the three optical radiation channels comprise one reception channel and two transmission channels, as in the claims 7 to 10 Further subject of the invention are the variants to the method described in claims 11 to 15 Further subject of the invention is a device for the implementation of the method, in the variants described in claims from 16 to 31 An advantage offered by the method subject of the invention, in the first type of embodiments, is the substantial independence of the measured distance from possible variations in the intensity of the optical radiation flux emitted by the transmitting channel The term "optical radiation' in this description is used to define the electromagnetic radiation whose wavelength is comprised in the range from the ultraviolet to the infrared The measuring method subject of the invention can be more clearly understood by reference to the description of an embodiment thereof, illustrated by way of a non limiting example in the attached drawings in which Fig 1 shows a principle scheme of a device according to the invention Fig 2 shows the sensitivity curves versus distance of the two receiving channels Fig 3 shows the distance measuring function than one can obtain using the method subject of the invention Fig 1 shows the principle scheme of a device able to implement the method of measuring subject of the invention, in a first variant using one transmitting channel and two receiving channels The quantity to be measured is the distance x between the device and the surface 4 The transmitting channel 1 and the two receiving channels 2 and 3 are mounted on the body 5 of the device, in such a way as to be positioned with respect to each other with the optical axes parallel to each other, laying in the same plane and being the optical axes of the receiving channels at distance dy1 e dy2 with respect to the axis of the transmitting channel The transmitting channel uses means for generating optical radiation, and is provided with optical means with such charactenstics as to form a beam having divergence angle α, an intensity distnbution substantially symmetrical about the axis and preferably showing a gaussian-like profile along any direction orthogonal to the The receiving channels 2 and 3, having substantially the same characteristics, use means of detecting optical radiation that are able to detect radiation of the wavelength emitted by the emitting diode The receiving channels may be equipped with optical means with characteristics similar to those of the transmitting channel, in this case the sensitivity distribution of the receiving beam is substantially symmetrical about the optical axis and preferably shows a gaussian-like profile along any direction orthogonal to said axis The use of transmitting and receiving beams having gaussian-like distribution is not a restrictive choice for the implementation of the measuring method subject of the invention, since it is possible to effectively use for that purpose beams having different characteristics The use of beams having gaussian-like profile distribution is an advantageous choice as this characteristic can be easily obtained by means of simple optical systems The signals from the receiving channels are connected to an electronic unit 6 equipped with means of processing said signals Moreover the electronic unit is equipped with supplying means of powering the optical radiation generating means connected to it In the configuration of the example herewith described, for simplicity sake, a solution where the transmitting and receiving beams have substantially equal divergence values is chosen, such condition being neither restrictive nor necessary for the implementation of the method subject of the invention Let us take as x-y plane the one where the optical axes of the transmitting and receiving channels lay, with the x axis parallel to said axes, the intensity and sensitivity respectively in the y-z plane, orthogonal to the optical axes, at the generic distance x is given by the relation where σ(x) is defined as follows σ (x) = x ■ tan — Being α the beam divergence, that is the angle from the axis where the value is reduced to 13,5% of the on-axis value The radiant flux incident on the area unit of the surface is given by the relation where Φ 0 = transmitting channel radiant flux k = proportionality constant f (x,y,z) = /(x.y,z) The radiant intensity of the area unit of the surface is given by i 9( χ , v,z) = p S - φIΛ χ ,y z) — π where s = surface reflectivity The irradiance on the generic receiving channel produced by the area unit of the surface is given by The sensitivity distribution of the generic receiving channel, referred to the surface, is described by the relation where dy = distance between the transmitting channel optical axis and the one of the receiving channel considered The flux at the generic receiving channel from the area unit of the surface is given by <p r (x,y,z) = H r (x,y,z) - f r (x,y,z) - A r where Ar= receiver surface area The total flux at the entrance of the geneπc receiving channel can be calculated integrating over the part of the surface interested by the beams and is given by the following relation The above relation can be written as follows by putting in evidence the terms not depending by the distance x Φ r (x) = A r -ps — o - g(x) π where This last function describes the relation between the radiant power collected by the receiver versus the distance from the surface The g(x) function relevant to the generic receiving channel shows a strong dependence by the distance dy between the optical axis of said channel and the optical axis of the transmitting channel By positioning two receiving channels at different distances dy with respect to the optical axis of the transmitting channel, the functions g(x) relevant to said channels result substantially different over assigned distance ranges Fig 2 shows, for example, the curves describing in arbitrary units, the functions g1(x) and g2(x), in a configuration where the beams have a divergence α = 30° and the distances dy1 and dy2 between the axes of the transmitting channel and the two receiving channels are respectively 1 5mm and 3 Omm The difference between the functions on a given distance range is apparent A similar result can be obtained on different distance ranges by the use of different arrangements of divergence values and between the axes distances of the beams To measure the distance x, the measuring method subject of the invention utilizes the difference between the functions g1(x) and g2(x), relevant to two receiving channels having their optical axes positioned at different distances with respect to the axis of the transmitter and parallel to it, being the measured values C1(x) and C2(x) of the fluxes collected by said receiving channels related to the values of said functions g1(x) and g2(x) by a proportionality constant, and utilizes a specific way of processing the measured values of the two fluxes collected by the two receiving channels such that the terms not dependent on said distance are eliminated, among which mainly the reflectivity coefficient of the surface A possible implementation of such processing procedure, illustrated by way of example and without restriction, is described by the following equation relating the distance measurement S(x) to the receiving channels measurements C1(x) and C2(x) |(Cl(x) + C2(x)) (Cl(x) - C2(x)) Fig 3 shows, by way of a non limiting example, the distance measurement obtainable by processing the measurements of the receiving channels according to the above illustrated procedure, in the same conditions as described for Fig 2 The distance measurement, obtainable by utilizing the method subject of the invention, shows advantageously very good linearity characteristics over large measurement ranges By referring again to Fig 1 , in a second vaπat of the method of the invention two transmitting channels and one receiving channel are used The quantity to be measured is again the distance x between the device and the surface 4 The position of the channels with respect to the surface is still as described for the first variant, and also all the theoretical explanation relating to the first variant still applies to this second vaπant According to this second variant the two transmission channels are activated alternately, the reception channel collects alternately the radiating flux rediffused by the two transmitters, the two transmission channels use means for generating optical radiation and the reception channel means for detecting optical radiation, as in the first vaπant, an electronic unit is provided to process the signals coming from the reception channel and to control the emission by the transmission channels The electronic unit measures the two fluxes coming from the two transmission channels independently from each other, and processes the measures obtained also according to the above formula giving the value of S(x) The reflectivity characteristics of the surface have the same effect for both the transmission channels on the amount of flux collected by the reception channel, so rendering the measuπng method independent of the reflectivity characteristics of the surface Using the measuring method subject of the invention, it is therefore feasible to get, by means of the measurement of the receiving channels fluxes, a signal being stπctly correlated to the distance to be measured and at the same time not dependent upon the reflectivity characteristics of the surface The measuring method subject of the invention can be utilized for the implementation of distance measuring devices according to different embodiments, some of which are described in the following by way of non limiting examples In the preferred embodiments described in the following, the optical axes of the transmitting and receiving channels lay in the same plane, and the transmitting channel is positioned on a side of the receiving channels, other embodiments may have the optical axes of the three channels parallel each other, but not laying on the same plane, or laying on the same plane with the transmitting channel positioned between the two receiving channels and at different distance from the axis of each of the reception channel In an embodiment the optical means of the transmitting and receiving channels may be advantageously made using three sections of optical fibre, one for each channel, each section having one of the terminations mounted in a holder having such a configuration, as to position said terminations with respect to each other according to the geometry provided for by the method subject of the invention, as to form a measurement probe The remaining terminations of said optical fibres are so connected the one pertaining to the transmission channel to means for generating optical radiation, those pertaining to the receiving channels to means for detecting the optical radiation Said means for generating and detecting the optical radiation are preferably housed in a suited body or housing, into which the electronic unit to which said means are connected may also be housed Said electronic unit is provided with means of acquiring the signals of the optical radiation detectors, with means of processing those signals, with means of powering the optical radiation generator and with means of generating electric output signals In a variant embodiment, the optical radiation generating and detecting means may be advantageously integrated into the electronic unit resulting in a conspicuous easing of manufacturing The optical fibres used may profitably be of the type made of plastic material (Plastic Optical Fibre) normally used for data transmission, specifically, the termination of this kind of fibres, having a diameter of 1mm and made with the optical termination surface flat and normal to the optical axis, are suited to form beams having such characteristics as previously described In a variant embodiment, the desired optical characteristics may be obtained by means of a different kind of working of the optical termination surface of the optical fibres, for example along a curved instead of flat surface, or by the addition of optical components as, by way of non limiting example, refraction lenses, refraction gradient index lenses (GRIN-rod lens), diffraction lenses or combinations thereof The means for generating the optical radiation may usefully consist of an emitting diode or LED, or a Laser diode, or a general purpose optical radiation source The optical radiation detecting means may usefully consist of photodiodes, or phototransistors or photodiodes with integrated transimpedance amplifier, or photodiodes with integrated hght-to-frequency converter, or similar optoelectronic devices able to detect radiation of the wavelength emitted by the means for generating the optical radiation In a variant embodiment the device implementing the method subject of the invention may be made as a single body or housing into which the transmitting and receiving channels and the electronic unit are housed The optical means of the transmitting and receiving channels, similarly to what seen for the previously described embodiment, consist of section of optical fibre, each of those fibres having a first termination mounted in the outer wall of the housing and positioned with respect to the others according to the geometry provided for by the method subject of the invention, io and the second termination connected to the means for generating or detecting the optical radiation therefore such optical fibre sections are entirely contained in the housing Also for the just described variant embodiment different optical characteristics of the transmitting and receiving channels beams may be obtained with specific working of i s the optical fibres terminations, or by the use of optical components as said for the previously described embodiment In a further variant embodiment the device may be made as a single body or housing, the optical means of forming the transmitting and receiving beam may be optical components like, by way of example and without restriction, refraction lenses, 20 refraction gradient index lenses (GRIN-rod lens), diffraction lenses or combinations of said components, and the means of generating and detecting the optical radiation may consist of commercially available optoelectronic components, being said optical components and said optoelectronic components suitably arranged together and mounted in one of the outer walls of the housing, and positioned with respect to each 25 other according to the geometry provided for by the method subject of the invention In a variant of the just described embodiment, the transmitting and receiving channels may consist of usually commercially available optoelectronic components of the so-called integrated optic type, that is having optical components manufactured in the component housing itself or anyway premounted on it, said components are 30 mounted in one of the outer walls of the housing and positioned with respect to each other according to the geometry provided for by the method subject of the invention In a variant embodiment, the optical radiation detecting means and the processing means can be made as a single component in the form known as integrated microcircuit In a further variant embodiment, the electronic unit may be provided with means for setting distance reference values and of means of comparing said values with the measured distance, and of means of generating signals or controls depending on the result of the above comparison, so as to detect and signal when the measured distance becomes larger or smaller with respect to said reference values, in this way a device may be made of the type known as proximity sensor or switch, advantageously provided with characteristics of msensitivity to the reflectivity coefficient of the measured surface The measuring method subject of the invention allows the implementation of devices and sensors for measuring different physical quantities when their measurement can be derived from a distance or length measurement by means of a suited conversion principle By way of example of these possible uses and without restriction, one may mention the measurement of acceleration by means of measuring the movement of a body connected by an elastic constraint to the structure holding the distance measuπng device, the measurement of pressure by means of measuring the deformation induced in a flexible diaphragm and the measurement of the vibrations of a body by means of measuring the distance of the surface of said body from a reference non moving structure to which the distance measuring device is mounted Naturally, the invention is not limited to the embodiments described and illustrated herein, but may be greatly varied and modified, particularly as regards construction, without departure from the guiding principle disclosed above and claimed below

Claims: CLAIMS 1 Method for measuring a distance from a surface, characterized in that three optical radiation transmission or reception channels are used, having a given emission or respectively reception divergence angle, said receiving channel(s) collecting the optical radiation rediffused by said surface towards which it is emitted by said transmission channel(s), and in that said transmitting channel(s) and receiving channel(s) are placed substantially at the same distance from said surface, with parallel optical axes, and the distances between the optical axes of said transmission channel(s) with respect to said receiving channel(s) are different 2 Method for measuring a distance as in claim 1 , characterized in that said three optical radiation channels comprise one transmission channel and a first and second reception channels 3 Method for measuring a distance as in claim 2, characterized in that the transmission channel is positioned sidewise with respect to the receiving channels 4 Method for measuring a distance as in claim 2, characterized in that the transmission channel is positioned in between the receiving channels 5 Method for measuring a distance as in any of the preceding claims, characterized in that said distance between the axes is twice between the optical axes of said transmission channel and one receiving channel with respect to that between said transmission channel and other receiving channel 6 Method for measuring a distance as in any of the preceding claims, characterized in that said distance is measured by using a formula of the following type Where x is the distance, S(x) the measured value of distance, C1(x) and C2(x) the measures of radiating power received respectively by the first and second receiving channels 7 Method for measuring a distance as in claim 1 , characterized in that said three optical radiation channels comprise one reception channel and a first and second transmission channels 8 Method for measuπng a distance as in claim 7, characterized in that said two transmission channels emit the optical radiation alternately 9 Method for measuring a distance as in claim 7 or 8, characterized in that the reception channel is positioned sidewise with respect to the transmission channels 10 Method for measuring a distance as in claim 7 or 8, characterized in that the reception channel is positioned in between the transmission channels 11 Method for measuπng a distance as in any of claims 7 to 10, characterized in that said distance is measured by using a formula of the following type /(Cl(x) + C2(x)) l( (Cl(x) - C2(x)) where x is the distance, S(x) the measured value of distance C1(x) and C2(x) the measures of radiating power received by the receiving channel, transmitted respectively by the first and second transmission channels 12 Method for measuring a distance as in any of claims 7 to 11 , characterized in that said distance between the axes is twice between the optical axes of said first transmission channel and the receiving channel with respect to that between said second transmission channel and the receiving channel 13 Method for measuring a distance as in any of the preceding claims, characterized in that the optical axes of all the optical radiation channels are on the same plane 14 Method for measuring a distance as in any of the preceding claims, characterized in that said divergence angle is substantially constant around the optical axes, and in that the optical radiation has a gaussian-like distribution with the distance from the optical axes 15 Method for measuring a distance as in any of the preceding claims, characterized in that the values of distance between the axes and divergence angle are chosen so as to optimize the radiating power values received by the receiving channels 16 Method for measuring a distance as in any of the preceding claims, characterized in that it is used for measuring a different phisical magnitude connected to said distance measure 17 Method for measuring a distance as in claim 16, characterized in that said different phisical magnitude is an acceleration, or a pressure, or a vibration 18 Device for measuπng a distance (x) from a surface (4), for carrying out the method of any of the preceding claims, characterized in that said three optical radiation transmission or reception channels (1 , 2, 3) are equipped with a termination towards said surface, respectively emitting and receiving optical radiation, mounted on a support or housing (5) keeping said terminations at a distance substantially equal from said surface (4), with parallel optical axes, so that the distances between the optical axes of said transmission channel(s) with respect to said receiving channel(s) are different 19 Device for measuring a distance (x) as in claim 18, characterized in that said support or housing (5) keeps said terminations in a position such that the optical axes are substantially on the same plane 20 Device for measuring a distance (x) as in claims 18 or 19 characterized in that said terminations are made by sections of optical fibre 21 Device for measuring a distance (x) as in claim 20, characterized in that said sections of optical fibre are of the plastic type 22 Device for measuring a distance (x) as in claim 21 , characterized in that said terminations are planar and perpendicular to the optical axes 23 Device for measuring a distance (x) as in claim 21 , characterized in that said terminations are curved 24 Device for measuring a distance (x) as in claims 18 or 19, characterized in that said terminations are made by optical elements, as refraction lenses, or gradient lenses, or refraction index gradient lenses, or diffraction lenses or their combinations 25 Device for measuring a distance (x) as in claims 21 or 22, characterized in that said terminations are made by integrated optics optoelectronic components 26 Device for measuring a distance (x) as in claims 18 or 19, characterized in that said transmission channel(s) use(s) means for generating optical radiation, and in that said receiving channel(s) use(s) means for detecting optical radiation 27 Device for measuring a distance (x) as in claim 26, charactenzed in that said means for generating optical radiation are made of LED diodes or laser 28 Device for measuring a distance (x) as in claim 26, characterized in that said means for detecting optical radiation are made of photodiodes, or phototransistors, or integrated transimpedance amplifier photodiodes, or photodiodes with integrated light- frequency conversion device 29 Device for measuring a distance (x) as in claim 26, characterized in that the connection between the means for generating optical radiation and the termination of said transmission channel(s), and between the means for detecting optical radiation and the termination of said receiving channel(s) is made of optical fibre - π - 30 Device for measuring a distance (x) as in any of claims from 18 to 29, characterized in that comprises in addition processing means for the signals coming from said means for detecting optical radiation, calculating said distance (x) 31 Device for measuring a distance (x) as in claim 30, characterized in that said processing means compπse in addition means for input of reference values for the distance and means for comparing said values with the measured distance, and means for generating signals or commands depending on the results of said comparation, so as to detect and report the overflow of said reference values by the measured distance 32 Device for measuring a distance (x) as in any of claims from 18 to 31 , characterized in that said support or housing (5) contains in addition said means for generating and detecting the optical radiation and their connections with said terminations and possibly also said processing means 33 Device for measuring a distance (x) as in any of claims from 18 to 32, characterized in that said means for detecting optical radiation and processing means can be implemented in one only chip component

Inventors: ARRICHIELLO VINCENZO, ARRICHIELLO, VINCENZO
Applicants: ARRICHIELLO VINCENZO, ARRICHIELLO, VINCENZO
Application year: 1996
Main classification: G01D5
IPC codes: G01B11, G01D5