Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
  • G01B11/026—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness by measuring distance between sensor and object
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
  • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
  • G01D5/268—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light using optical fibres

Definitions

• 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
• 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
• 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 miniatu ⁇ zable, 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
• the three optical radiation channels comprise one transmission channel and two reception channels, as in the claims 2 to 6
• 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
• 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
• 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 ⁇ , 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 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.
• ⁇ (x) x ⁇ tan —
• 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
• the total flux at the entrance of the gene ⁇ c receiving channel can be calculated integrating over the part of the surface interested by the beams and is given by the following relation
• 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
• 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
• 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
• 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 va ⁇ ant, 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 measu ⁇ ng method independent of 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
• 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
• 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
• 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
• the termination of this kind of fibres 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
• 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
• 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
• 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,
• refraction gradient index lenses GRIN-rod lens
• 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
• the optical radiation detecting means and the processing means can be made as a single component in the form known as integrated microcircuit
• 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

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Length Measuring Devices By Optical Means (AREA)
• Measurement Of Optical Distance (AREA)

Applications Claiming Priority (3)

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• 1995
  • 1995-11-03 IT IT95SP000012A patent/IT1283536B1/it active IP Right Grant
• 1996
  • 1996-10-29 WO PCT/EP1996/004717 patent/WO1997017589A1/en not_active Application Discontinuation
  • 1996-10-29 EP EP96937297A patent/EP0861418A1/de not_active Withdrawn
  • 1996-10-29 AU AU74958/96A patent/AU7495896A/en not_active Abandoned

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