USRE35816E - Method and apparatus for three-dimensional non-contact shape sensing - Google Patents

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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
  • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
• • 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
  • G01B11/002—Measuring arrangements characterised by the use of optical techniques for measuring two or more coordinates
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
  • G01S17/06—Systems determining position data of a target
  • G01S17/46—Indirect determination of position data
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/88—Lidar systems specially adapted for specific applications
  • G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/481—Constructional features, e.g. arrangements of optical elements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/481—Constructional features, e.g. arrangements of optical elements
  • G01S7/4811—Constructional features, e.g. arrangements of optical elements common to transmitter and receiver
  • G01S7/4813—Housing arrangements
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B34/00—Computer-aided surgery; Manipulators or robots specially adapted for use in surgery
  • A61B34/20—Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
  • A61B2034/2046—Tracking techniques
  • A61B2034/2055—Optical tracking systems
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B34/00—Computer-aided surgery; Manipulators or robots specially adapted for use in surgery
  • A61B34/20—Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
  • A61B2034/2068—Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis using pointers, e.g. pointers having reference marks for determining coordinates of body points
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/86—Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
  • G01S5/16—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using electromagnetic waves other than radio waves
  • G01S5/163—Determination of attitude
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/481—Constructional features, e.g. arrangements of optical elements
  • G01S7/4817—Constructional features, e.g. arrangements of optical elements relating to scanning

Definitions

• This invention relates to optical mensuration devices in general, and in particular to an improved method and apparatus for the optical mensuration of the surface shape of a three-dimensional object.
• mensuration systems exist in the prior art for sensing the locations of surface points on three-dimensional solid objects in relation to a predefined fixed reference frame or coordinate system for input into an application system, such as a computer or other device for measurement or analysis.
• an application system such as a computer or other device for measurement or analysis.
• one type of mensuration system that can be used to determine the location of a single point on the surface of an object includes the use of a narrow projected beam of light to illuminate a tiny area or spot on the surface of the object.
• a lens in the system is positioned on an optical axis oblique to the axis of the projected beam and is used to focus the reflected light from the illuminated spot onto a photoelectric sensor or onto a linear array of sensors.
• the location of the illuminated point with respect to the predetermined reference frame can be determined by computing the distance of the illuminated surface point from the origin of the light beam which, of course, is known. Examples of such point illumination optical mensuration systems are found in the following U.S. Pat. Nos.
• a variant of the above-described systems projects a thin beam of light in a single plane which, of course, is incident as a line, as opposed to a point, on the surface of the object being scanned.
• the intersection of this plane of light with the object's surface thus forms a brightly illuminated contour line.
• a two-dimensional electronic video camera or similar device whose optical axis is not coincident with the axis of the illuminating beam, detects the image of this contour line. Again, since the optical axis of the camera is not coincident with the axis of the illuminating light beam, it views the contour line from an oblique angle, thus allowing location of the contour line to be precisely determined in relation to the known position of the beam projector.
• either the measuring apparatus or the object is panned along (or rotated about) an axis through the object. While these line scanning devices share similar drawbacks with the point scanning devices previously described, they do operate much faster, gathering a larger number of sample points during a given scanning interval. Unfortunately, the accuracy of each surface sample point is limited by the relatively low resolution of the two-dimensional charge coupled device (CCD) sensors found in most video cameras, which is typically in the range of 1 part in 512. Even worse, these systems still suffer the disadvantages of the point scanning systems in that either the scanning head or the object must be relocated or re-oriented to completely and accurately record all of the surface details of an object.
• CCD charge coupled device
• Still other mensuration systems track the positions of specific points in three-dimensional space by using small radiating emitters which move relative to fixed receiving sensors, or vice versa. Such radiation emitters may take the form of sound, light, or nutating magnetic fields.
• Another mensuration system uses a pair of video cameras plus a computer to calculate the position of homologous points in the pair of stereographic video images. See, for example, U.S. Pat. Nos. 4,836,778 and 4,829,373.
• the points tracked by this system may be passive reflectors or active light sources. The latter simplifies finding and distinguishing the points.
• the paper by Fuchs, et al, (1978) describes a basic method of tracking a light source in three-dimensional space.
• the method is based on using three or more one-dimensional sensors, each consisting of a cylindrical lens and a linear array of photodetectors, such as charge coupled devices (CCDs), to determine the location of the currently radiating source.
• CCDs charge coupled devices
• the scanning head of such an improved system should be hand-held to allow the operator to easily move the scanning beam over some of the more complex surface details of the object while dispensing with the need for the expensive, cumbersome, and high precision scanning head positioning apparatus currently required.
• Such a hand-held scanner must also provide the accuracy and precision associated with currently available optical mensuration systems, that is, it must be able to accurately measure and precisely locate the surface details of the object in relation to the predetermined reference frame.
• an object of the present invention to provide an improved, non-contact, three-dimensional optical mensuration system capable of accurately sensing the surface shapes of three-dimensional objects without the numerous drawbacks associated with the prior art systems.
• a still further object of this invention is to provide a portable, hand-held, and hand-maneuverable scanner for the three-dimensional, non-contact shape-scanning and/or mensuration of three-dimensional objects.
• the apparatus for three-dimensional, non-contact shape sensing of this invention may comprise a hand held scanning head with a light source for projecting a scanning light beam over the surface of the object being scanned.
• Two spot detectors mounted on the hand-held scanning head are operative to detect the position of the illuminated spot on the surface of the object in relation to the scanning head.
• a coordinate computer connected to the scanning head and to the pilot light detectors receives data from the spot detectors and calculates the position of the illuminated spot with respect to the scanning head.
• the coordinate computer then calculates the various positions and orientations of the scanning head in relation to the predetermined coordinate system on a real time basis from the data received from the pilot light detectors.
• the coordinate computer calculates the position of the illuminated spot in relation to the predetermined coordinate system by correlating the position of the illuminated spot in relation to the scanning head with the position of the scanning head in relation to the predetermined coordinate system.
• the method of this invention includes the steps of sweeping a scanning beam projected from the hand held scanning head over the surface of the object being scanned to illuminate a spot on the surface of the object, detecting the position of the illuminated spot with respect to the scanning head, detecting the position of the scanning head in relation to a predetermined coordinate system, and computing the position of the illuminated spot in relation to the predetermined coordinate system by correlating the position of the illuminated spot in relation to the scanning head with the position of the scanning head in relation to the predetermined coordinate system.
• FIG. 1 is a block diagram of the optical mensuration apparatus of the present invention showing the major components
• FIG. 2 is a perspective view of the hand held scanning head of the present invention, showing how it can be positioned to direct the scanning beam onto the surface of the object being scanned;
• FIG. 3 is a plan view of the scanning head of the present invention with the top surface broken away to more clearly show the arrangement of the optical projecting apparatus and the spot detectors;
• FIG. 4 is a schematic perspective representation of one of the one-dimensional photodetectors of the present invention.
• FIG. 5 is a schematic block diagram of the optical mensuration apparatus of the present invention showing in detail the functions and operations of the control unit and coordinate computer;
• FIG. 6 is a graph of signal strength vs. location on the detector surface for a typical light detector used by the optical mensuration apparatus of the present invention.
• the optical mensuration apparatus 10 of the present invention is shown schematically in FIG. 1 and comprises a hand-held or moveable scanning head 12 housing light beam projecting apparatus 14 (not shown in FIG. 1, but shown in FIG. 3), two one-dimensional spot sensors or detectors 16, 18, and three pilot light emitters 20, 22, and 24.
• Three remotely located, one-dimensional pilot light sensors 26, 28, and 30 are mounted in fixed, spaced-apart relation to each other and are located at known positions with respect to a predetermined reference coordinate system or frame 80. These three pilot sensors 26, 28, and 30 sense the light projected by the individual pilot light emitters 20, 22, and 24 and generate electrical output signals from which are derived the location of the scanning head 12 with respect to the fixed coordinate system 80.
• a control unit 32 connected to the moveable scanning head 12 via data line 46 and connected to the remotely located sensors 26, 28, and 30 via data lines 48, 50, and 52, respectively, synchronizes the time multiplexing of the three pilot emitters 20, 22, and 24, controls the operation of the beam projecting apparatus 14, and receives data from the two spot sensors 16, 18 on scanning head 12, as will be completely described below.
• a coordinate computer 34 connected to control unit 32 by data line 54 calculates the three-dimensional spatial coordinates of the illuminated spot 36 in relation to the predetermined coordinate reference frame 80, which position information can then be used by an application system 82.
• the light beam projecting apparatus 14 housed in the hand held scanner head 12 directs a narrow beam of light or scanning beam 42 onto the surface 40 of object 38 to illuminate a small portion or spot 36 on the surface 40.
• Reflected light 43 from illuminated spot 36 is detected by the two one-dimensional spot sensors or detectors 16, 18 mounted on scanner head 12. These sensors 16, 18 sense the location of the illuminated spot 36 with respect to the position of the moveable scanner 12 by measuring the relative angular parallax of the reflected light 43 from illuminates spot 36.
• the spatial position and orientation of the moveable scanner head 12 at that same instant are determined by measuring the locations of the three time multiplexed pilot light emitters 20, 22, and 24 relative to the known positions of the pilot light sensors 26, 28, and 30.
• the parallax data from each of the sensors 16, 18, 26, 28, and 30 are ultimately fed to the coordinate computer 34, which determines the position of the illuminated spot 36 with respect to the predetermined reference frame by correlating the position of the illuminated spot 36 in relation to the scanner head 12 with the position of the scanner 12 in relation to the fixed pilot light sensors 26, 28, and 30, which are positioned in relation to the predetermined reference frame 80 at precisely predetermined locations at conveniently spaced distances from each other and from the object 38 and the hand-held scanner 12. If the computer can make these location or position calculations very fast, the operation can be performed over and over again in sequence as the scanner head 12 moves in relation to the object, thus resulting in effectively real time mensuration of the object as the scanner head 12 moves.
• the optical mensuration apparatus 10 of the present invention dispenses with the need for high precision head positioning apparatus and the complex and expensive mechanical structure typically associated therewith. Further, the hand-held scanner, 12 is easily manipulated by the operator to direct the scanning beam 42 over complex, interior, or blind surface details, which would otherwise be difficult to scan, thus speeding the scanning operation.
• the hand-held scanner head 12 houses the light beam projecting apparatus 14 (FIG. 3), the two one-dimensional spot sensors or detectors 16, 18, and the three pilot light emitters 20, 22, and 24.
• a handle 44 allows the scanner head 12 to be easily manipulated by the operator to guide the scanning beam 42 over the various shapes and hidden contours of the surface 40 of object 38.
• the light beam projecting apparatus comprises a helium-neon (He-Ne) laser 56 to generate collimated scanning beam 42.
• He-Ne helium-neon
• other devices could be used to produce the spot-like scanning beam as would be readily apparent to persons having ordinary skill in the art.
• laser 56 could be replaced by a light emitting diode (LED) and associated collimating lens.
• LED light emitting diode
• a planar mirror 58 which could be optionally pivotally mounted as shown in FIG.
• a rotating many-faceted mirror 60 which directs, or scans beam 42 over the surface 40 in a single plane relative to the scanner 12 (i.e., the plane of the paper in FIG. 3).
• the number of sides of the rotating, many-faceted mirror 60 determines the angle through which scanning beam 42 sweeps.
• the pentagonal mirror shown in FIG. 3 will sweep the beam through a 144-degree angle. More sides will sweep the beam through smaller angles.
• other scanning paths are possible by using irregularly shaped mirrors or multiple rotating mirrors, and the present invention should not be regarded as limited by the particular scanning apparatus shown and described herein.
• the rotating mirror 60 in the preferred embodiment 10 is rotated in the direction indicated by arrow 62 by a simple, unsynchronized motor (not shown).
• planar mirror 58 may be optionally pivotally mounted such that it can be swung out of the beam path to position 58' (shown in broken lines in FIG. 3) to inhibit the scanning action of the beam 42. With the mirror at position 58' the beam 42 will exit straight out aperture 64 in scanner 12 which can then be used as a point-type scanner or as a noncontact pointer for identifying some single point of interest on the surface 40 of object 38.
• the details of the one-dimensional spot detectors 16, 18 are best understood by referring to FIG. 4. Actually, all of the one-dimensional sensors 16, 18, 26, 28, and 30 used in the preferred embodiment 10 of the present invention are identical to the one-dimensional spot detector 16 in every respect. Therefore, for the purpose of giving a detailed description of this embodiment, only the sensor 16 is shown and described in detail since the remaining sensors 18, 26, 28, and 30 have identical features.
• the one-dimensional sensor 16 comprises a cylindrical lens 66 that has a longitudinal axis 74 which is orthogonal to the optical axis 76 of the sensor 16.
• a linear photodetector 68 such as a charge coupled device (CCD) with several thousand elements, or a similar device capable of linear light detection with an elongated aperture 78 is positioned in such a manner that optical axis 76 passes through aperture 78 and such that the long axis of aperture 78 is orthogonal to the plane containing the longitudinal axis 74 of lens 66.
• the incident light beam 43 reflected from illuminated spot 36 is then focused by the cylindrical lens 66 into a real image line 72 on the surface 70 of linear photodetector 68, which is a characteristic of this type of lens.
• the CCD detector 68 then generates a signal, such as the one shown in FIG. 6, that is related to the position of real image line 72 on the surface 70 of photodetector 68, thus characterizing the location of the image itself. That is, those elements of the detector 68 illuminated by the real image line 72 will generate a strong signal, while those not illuminated will generate a weak signal. Thus, a graph of signal strength vs. location on the surface of the CCD will resemble the signal peak curve 100 shown in FIG. 6. Note that the "zero" signal level 102 is never quite zero due to the effects of background light and other imperfections in the sensor. In any event, since the image of illuminated spot 36 is focused into line 72, only the horizontal displacement of spot 36 from optical axis 76 is measured by detector 68, hence the designation "one-dimensional detector.”
• a single one-dimensional detector 16 can only locate the plane on which spot 36 particular beam lies, but detector 16 cannot, by itself, determine the unique location or position in space on which point 36 is located. To precisely locate the location in space of point 36 would require three such detectors postitioned in spaced-apart relation to each other, since the intersection of three planes defines a point. However, if the plane containing the aperture 78 of detector 16 is in the same plane as the scanning beam 42, only two detectors are required to uniquely locate the position of spot 36. Therefore, in the preferred embodiment 10 of the present invention, the apertures 78 of the respective photodetectors 16, 18, lie in the same plane as the scanning beam 42, thereby allowing the exact point in space of illuminated spot 36 to be determined with only two detectors 16, 18.
• the three pilot light emitters 20, 22, and 24 can be high intensity light emitting diodes (LEDs), which are preferably time multiplexed or strobed by control unit 32 in a predetermined manner such that only one pilot light LED is "on" or emitting light at any one time.
• the light emitted from any one of these emitters 20, 22, and 24 is detected by each of the three pilot light detectors 26, 28, and 30, which then determine the position of that particular emitter in relation to the known positions of the detectors 26, 28, and 30 at the instant in time that it is strobed or illuminated.
• the pilot light detectors 26, 28, and 30 are mounted so that their optical axes are not collinear.
• two pilot light detectors such as detectors 26, 30 in FIG. 1, are situated such that their respective axes 74 (FIG. 4) are in parallel spaced-apart relation, with the third detector 28 situated between the first two, but with its axis 74 perpendicular to the first two.
• each of the detectors 26, 28, and 30 then determine a unique plane in which the given pilot emitter lies, the intersection of which defines the exact location of that illuminated emitter.
• the optical mensuration system 10 of the present invention determines the orientation of the scanning head 12 in three-dimensional space by using the three (3) pilot emitters 20, 22, and 24, whose relative positions on the scanning head 12 are fixed and known. Consequently, when each of the emitters 20, 22, and 24 are rapidly turned on in sequence, the sensors 26, 28, and 30 can detect the exact position of each emitter in turn, thus determine the exact location and orientation of the scanning head 12.
• the detectors 26, 28, 30 locate the position of that particular illuminated pilot light only. If the strobe rate, that is, the frequency at which the emitters 20, 22, 24 are turned on and off in sequence, is fast enough, the detectors 26, 28, and 30 can, for all practical purposes, determine the position and orientation of the scanning head 12 at any instant in time.
• the detectors 26, 28, 30, need only distinguish which of the pilot light emitters 20, 22, 24 is “on” or illuminated at any one time. In the preferred embodiment 10 of the present invention, this function is accomplished by strobing or illuminating each of the emitters 20, 22, 24 in sequence.
• other methods could be used to allow the detectors 26, 28, 30 to distinguish the respective pilot light emitters 20, 22, 24 from one another. For example, different colors of light could be used in conjunction with detectors capable of distinguishing those particular colors or wavelengths of light.
• the respective pilot light emitters 20, 22, 24 could be modulated with a unique "tone" for each emitter.
• the control unit 32 or coordinate computer 34 could then be programmed to demodulate the tone, thus determine to which particular emitter 20, 22, or 24 the position signal belongs. Numerous other methods of distinguishing the pilot light emitters 20, 22, and 24 are possible and would be readily apparent to persons having ordinary skill in the art. Therefore, the present invention should not be regarded as limited to the particular strobing method shown and described herein.
• control unit 32 supplies power to the light beam projecting apparatus or source 14, the beam spot sensors 16, 18, the pilot light emitters or sources 20, 22, and 24, and the pilot light sensors 26, 28, and 30.
• the control and synchronization unit 84 and light source sequencer 86 time multiplexes or strobes the beam projecting apparatus 14 and the pilot lights 20, 22, and 24 individually, as described above, so that the position and orientation of the scanning head 12 can be determined from the signals received from pilot light sensors 26, 28 and 30.
• the angular data signals received from the pilot light sensors 26, 28, and 30 and from the spot sensors 16, 18, are converted by analog to digital converter 88. Actually, five analog to digital converters are used, as shown in FIG. 5, but only one is labeled and described herein for brevity, since the other four analog to digital converters are identical and are used to convert the signals from sensors 28 and 30 and 16 and 18, respectively.
• the control and synchronization unit 84 also controls five switches, of which switch 90 is typical, which store all digital data received from the sensors 26, 28, and 30 and 16 and 18 when the pilot light emitters and scanning beam 42 are "off,” and stores these data in background memory 92. Then, when the pilot light sources and scanning beam are illuminated in sequence by light source sequencer 86, the control and synchronization unit 84 changes the state of switch 90, which then redirects the data from the five sensors to the subtraction unit 94. Subtraction unit 94 substracts the "background" data from the illuminated data, thus resulting in a signal relatively free from background noise signal 102 (FIG. 6), since it has been subtracted from the signal.
• the first-last over-threshold unit 96 computes the location of the real image line 72 on the CCD sensor 68 (FIG. 4) by measuring the locations of the edges 104, 106 of the signal blip 100 (FIG. 6) generated by the CCD sensor based on a predetermined threshold signal level. The first-last over-threshold unit 96 then averages the distance between the two edges to find the center of the signal peak, which is often dipped, as shown in FIG. 6. This particular method of determining the center of the signal peak is well known in the art and will not be described in further detail.
• control unit 32 (FIG. 5) transmits the position data to the coordinate computer 34. That is, when the coordinate computer 34 is ready to compute the current location of the illuminated spot 36 on the object, the latest angular data from all sensors are provided for analyzation. If the spot sensors 16, 18, or the pilot light sensors 26, 28, and 30, generate data faster than the control unit 32 can process them, the angular data are simply discarded.
• the coordinate computer 34 calculates one-dimensional positions for each light source based on the location of the signal peak from each respective sensor. These one-dimensional positions are then used to calculate the three-dimensional spatial coordinates for the illuminated spot 36 and for the scanning head 12 in relation to the predetermined coordinate system 80, by coordinate transformation methods which are well-known in the art.
• the output from the coordinate computer 34 can be in any form desired by the operator or required by the application system 80, such as XYZ coordinate triples based upon some predetermined stationary rectangular coordinate system.
• the operation of the optical mensuration apparatus of the present invention is as follows. Upon illumination of a spot 36 on the surface 40 of object 38, the two spot sensors 16, 18 inside the scanner head 12 sense the angular position of the illuminated spot 36 at a given instant in time. The signals from these spot sensors 16, 18, are directed to the control unit 32 via data line 46. Next, the pilot light detectors 26, 28, and 30 are used to sense the individual positions of the three pilot light emitters 20, 22, 24 in sequence as described above. That is, each pilot light detector 26, 28, 30, measures the angle of rays from each of three pilot light emitters 20, 22, 24, mounted on the scanner 12. The angular data from each of these sensors 26, 28, and 30 are also directed to control unit 32 via data lines 48, 50, and 52.
• control unit 32 converts the angular data from each of the sensors 16, 18, 26, 28, and 30, which is in analog form, to digital data and tags these data with information identifying their respective sources. These converted digital data are then processed by removing the background noise and by using known signal detection methods to determine the center of the signal peak, thus the location of the image line 72 on the detector 68. These position locations of the centers of the respective signal peaks from each detector 16, 18, 26, 28, and 30 are then directed to coordinate computer 34 via data line 54, which then computes the current location of the illuminated spot 36 with respect to the predetermined coordinate system 80. Sequential calculations and beam spot position determination can be made as fast as the computer can do so, thus many such points on the surface of the object can be determined as they are scanned almost on a real time basis. These position data can be stored in computer memory, recalled, and correlated together to produce an image of the object in precise reproduction detail, or various points or other features on the object can be mensurated or used in any manner desired.
• cylindrical lenses could be used which have been longitudinally curved along an arc with a radius equal to the focal length of the lens.
• the surfaces of the photodetectors could also be curved, thus allowing the images of distant light sources to remain in sharp focus regardless of their positions.
• Various measurements of the detector outputs are also possible. For example, the angle of peak intensity, the intensity-weighted average, or the average of the minimum and maximum angles where the intensity is over some predetermined threshold value could be used.
• numerous enhancements of the digital data are possible by programming the coordinate computer to make the appropriate enhancements, as would be obvious to those persons having ordinary skill in the art.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• General Physics & Mathematics (AREA)
• Computer Networks & Wireless Communication (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Electromagnetism (AREA)
• Length Measuring Devices By Optical Means (AREA)
• Length Measuring Devices With Unspecified Measuring Means (AREA)
• Testing Or Measuring Of Semiconductors Or The Like (AREA)

Abstract

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Citations (32)

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• 1990
  • 1990-10-15 US US07/597,505 patent/US5198877A/en not_active Ceased
• 1991
  • 1991-10-11 WO PCT/US1991/007511 patent/WO1992007233A1/en active IP Right Grant
  • 1991-10-11 JP JP3518467A patent/JP2974775B2/en not_active Expired - Fee Related
  • 1991-10-11 CA CA002094039A patent/CA2094039A1/en not_active Withdrawn
  • 1991-10-11 EP EP91920138A patent/EP0553266B1/en not_active Expired - Lifetime
  • 1991-10-11 DE DE69126035T patent/DE69126035T2/en not_active Expired - Fee Related
  • 1991-10-11 AT AT91920138T patent/ATE152823T1/en not_active IP Right Cessation
• 1995
  • 1995-03-30 US US08/415,126 patent/USRE35816E/en not_active Expired - Lifetime

Patent Citations (32)

Non-Patent Citations (11)