Patent Application: US-201414436155-A

Abstract:
a method for performing three - dimensional measurements that includes : projecting with a projector of reset non - overlapping images oriented alone the one of longitudinal axis with a constant distance in between , registering the light from the projector reflected from the object using at least one camera placed with formation of a triangulation angle between the central beam of the projector and central beams of the cameras , the cameras are arranged at an angle to the projector as in the vertical and horizontal planes . each of the images projected on the measured object is a discrete sequence of geometric elements , and the identification of images taken by the camera of these elements is made due to the projected shift . the method provides for reduced distortion of measurements for y - axis and enhanced sensitivity for z axis , mad almost complete elimination of errors i . e . improved accuracy at measurements .

Description:
a method for measurement of linear dimensions of three - dimensional objects is as follows . each image projected by the projector consists of periodically ( uniformly ) projected discrete elements : dots , dashes ( similarly , segments of the image ) or intervals between these elements along an imaginary straight path ( imaginary straight line ). these elements are arranged with a spacing tx along the x - axis of the image and the spacing ty along the y - axis . in the proposed method , when projecting images in a sequence ( along two non - intersecting paths ) of projected discrete geometric elements such as dots , and position of the camera 6 at an angle to the projector 5 , not only in the vertical plane , but also in the horizontal one , can be used to increase the used shill length 17 , i . e . the value of a possible shift of the dot 8 until it crosses the possible adjacent shift lengths , i . e . positions of other dots in the fig2 . thus , when projecting an image to the object 16 as a sequence of discrete elements , for example dots , it is possible to use the area of receiving array 12 of the camera 6 more uniformly and efficiently and increase the sensitivity of the 3d scanner 30 along the z - axis , as z coordinate is contained in the possible shift of the dot 8 in the shift length 17 in the receiving array 12 of the camera 6 . it can be seen on future 2 how a . shift length 17 of a possible shift of a dot passes through the area on the receiving array 12 , i . e ., uses an area in the receiving array 12 that typically is occupied with the projected path elements and the shift length . also in fig2 it can be observed how much the possible shift length 17 is greater than the shift length 19 . for 3d scanner 30 in fig1 the working area 7 is given in depth , i . e . for the z - axis . the working area corresponds to the depth of field of the lens . the depth of field of the lens may be a reference value of the camera lens ( the nominal value indicated in the camera &# 39 ; s technical data sheet ). depth of field of the camera lens tz in each particular case can be determined for example , as : tz = 2dc /( f / s ) 2 where d is the area of camera aperture ( m 2 ), c is the size of a pixel in the camera ( m ), f is the focal length of the camera lens ( m ), s is the distance from the projector 5 to the point intersection of the central beams 11 , 10 of the projector 5 and camera 6 ( m ). coordinates z 1 and z 2 are the boundaries of the working area . in this working area , the object 16 is measured by three coordinates . it is assumed that the scanner 30 does not make any measurements outside this area . working area usually looks geometrically as a spatial region with intersection of beams from the projector 5 that forms the image and the beams limiting the field of view of the camera 6 . in order to increase the working area in depth , it is allowed to include an area in which at close range the camera 6 can capture the object 16 only partially , and at long range the projector 5 could not light the entire surface of the object 16 to be captured by the camera 6 . the point of intersection of the central beam 11 of the optical system of the camera 6 and the central beam of the optical system of the projector 5 is located in the middle of the working area . focusing : distance from the light source 1 of the scanner 30 to the mid - line of the area indicated in fig1 with letter s , this distance is typically used for focusing lenses of the camera 6 and the projector 5 . the images drawn on the transparency 3 is projected by the projector 5 on the object 16 . the object 16 is shown in fig1 as a section , and in fig3 the object 16 is shown in an isometric view . object 16 is composed of three parts , or planes . the median plane 15 passes through the point of intersection of the central beam 11 of the optical system of the camera 6 and the central beam 10 of the projector 5 at the focusing distance s ( indicated in fig1 ) from the scanner 30 , the plane 13 is located at a greater distance from the scanner 30 than the median plane 15 , and the plane 14 is closer to the scanner 30 than the median plane 15 . the projected images of the dots 8 and 9 can be seen on the receiving array 12 of the camera 6 . depending on the distance between the scanner 30 and one or another part of the object , dots 8 and 9 may be captured by different pixels of the receiving array 12 of the camera . for example , if we project a dot 8 at the object 16 , we will observe the dot 8 at different locations on the receiving array 12 of the camera 6 in dependence on which plane the dot will be reflected : the median plane 15 or the plane 14 . areas on the receiver array 12 to which the dots 8 , 9 can be projected the shift length 17 , 18 of these dots . before scanning the object 16 , calibration of the scanner 30 must be performed . during calibration , the system can be positioned in place , all the possible positions of the dots to be recorded and compated , i . e . recording individual dot shift length 8 , 9 on an image obtained from the camera 6 to select the optimal distance to the object 16 . this information is subsequently used when working with the object 16 . for this purpose a plane ( e . g . screen ) is installed in front of the system consisting of the camera 6 and the projector 5 perpendicular to the optical axis of the projector 5 or the camera 6 , and this screen is moved along the axis of the projector 5 or camera 6 . movement of the screen plane is provided by high - precision handling equipment , such as numerically controlled machine tool that allows obtaining coordinates with high accuracy of a few microns due to high - precision handling . this process includes recording the dependence of the is shift or shift length for dots in the image of the camera 6 depending on the distance from the scanner 30 including the camera 5 and the projector 6 . this calibration process also takes into account the distortion ( violation of geometric similarity between the object and its image ) and other distortions of lenses of the camera 6 and the projector 5 . in the two - dimensional case , the dot shift length 19 in the image would look like the shift length shown in fig2 . in order to accurately measure object 16 in three coordinates , it is necessary that the shift length 17 , 18 do not overlap in the image created by the camera 6 , regardless of where the object 16 or part of the object 16 are in the working area of the scanner 30 . to fulfill this condition , it is necessary to choose right spacing distances tx and ty between the dots along the x and y axes of positions of the dots in the image projector 5 , and angles and base distance between the projector 5 and the camera 6 along the x and y axes . these options can he selected using the correlations tg αy = ty / z 1 − z 2 , tgαx = tx / z 1 − z 2 . basic distances ly = s * tg αy and lx = s * tg αx where s is the focusing distance from the light source 1 of the scanner 30 to the mid - line of the area or the distance from the light source 1 of the scanner 30 to the intersection of the central beams 10 , 11 of the camera 6 and the projector 5 . fig2 shows that if the camera 6 is positioned directly below the projector 5 , i . e . if the angle αx is 0 , then the dot shift length 19 is shorter than the dot shift length 17 . it follows that it is more efficient to position the camera 6 under the angle αy and αx to the projector 5 , i . e . camera 6 should be placed at an angle to the projector 5 not only in a vertical plane but also in a horizontal one . due to this arrangement of the camera 6 relative to the projector 5 it is possible to measure the z coordinate more accurately , as the shift length 17 of a dot is longer in the same area and more pixels correspond to the image of the camera 6 for the shift length 17 , i . e ., it is possible to make more measurements using the receiving array 12 of the camera 6 for the same area along the z axis . fig3 shows the image observed by the camera 6 with the view from the camera 6 . the projector 5 projects the image consisting of dots on the object 16 , and the camera 6 is located at the angle αy and the angle αx to the x and y axes . in fig3 it is possible ( for illustration purposes ) to observe the grid in the nodes of which dots are located . this grid corresponds to the position of the points that would exist if the object 16 consists only of the median plane 15 . for example , the dot 8 is caught in the plane 14 which is closer to the projector 5 than the median plane 15 , so it is moved above at the camera image 6 . the shift of the dot is drawn with the arrow 8 in fig3 . possible ( punctured ) position of the dot 8 in the case of a continuous plane 15 of the object 16 , i . e ., the estimated position that would be possible if the dot is projected on the median plane 15 and is at the beginning of the small arrow at the diagram , and the position of the dot reflected from the plane 14 is at the end of the arrow . it is also possible to observe the shift of the dot 9 , which is projected on the plane 13 . for the dot 8 , there is a shift length 17 along which it can move . it can be seen in fig3 that the point 8 may take any position on the shill length 17 and thus will not cross with the possible shift lengths and positions of other points . to increase the dot density and thereby the accuracy of measurement of small sized items , it is possible to use a second camera 28 positioned at another angle relative to the projector 5 , different from the angle of the first camera 6 . in this way it is possible to increase , for example , the density of the dots twofold , and shift length of dots will intersect , but the second camera 28 will allow resolving the uncertainty in the points of intersection . fig4 shows the points 22 and 23 with the shift lengths intersecting the in the image of the same camera 6 , but this uncertainty can be resolved by using the image with the second camera 28 , which is positioned at the angle − αx to the projector 5 , i . e . with opposite sign than the first camera 6 , and shift lengths shown with dotted lines in the fig4 do not intersect for these two points in the second camera 28 . for greater increase in the density of the slide a third camera 29 can be used to test and improve the positions of found dots , and a color camera 26 to capture the texture of surface of the object 16 , located between the projector 5 and the camera 28 farthest from the projector 5 . it is possible to produce an image that is projected by the projector 5 with strokes or stripes ( lines ), between which light dots 24 are arranged , as shown in fig5 . points can be dark if the picture is negative . these points appear as gaps in the lines of paths . it is possible to produce an image with stripes crossed with vertical lines 25 . these strokes 25 or gaps in the line paths are shifted in the image from the camera 6 similar to dots described above . in order to understand which section in the image from the camera 6 and which number of the period are correspond to each other , it is necessary need to follow along the shift length to the right or to the left until the next break or stroke and to determine the period by its position at the shift length 17 or 18 . proposed layout diagrams for the cameras 6 , 26 , 28 , 29 and the projector 5 in the scanner 30 are shown in fig6 and 7 . it can be seen that for each camera 5 , 26 , 28 , 29 there are base distances along the x and y axes , i . e . there are different angles between each central beam of the cameras 25 , 26 , 28 , 29 and the central beam of the projector 5 in two planes , horizontal and vertical . camera 26 does not capture the image projected by the projector 5 . but captures the texture , i . e . colors of the object 16 . the light source in the projector 5 can be of pulsed type and pulse period can be a fraction of a second the camera 26 captures the texture with a time delay of a few fractions of a second and does not capture the light from the source of the projector 5 . in order to obtain a quality color image of the object 16 , a circular flash 27 is installed around the camera 26 , being made of pulsed white light sources which are also triggered in sync with the camera 26 , i . e ., with a certain delay relative to the light source of the projector 5 . synchronization of cameras 6 , 26 , 28 , 29 and light sources of the projector 5 , as well as their delay values are controlled with the controller 36 . fig6 shows a proposed diagram of the 3 d scanner 30 , front view , with two cameras 6 and 28 , images from which are used to calculate the 3d image . fig7 shows a proposed diagram of the 3 d scanner 30 , front view , with three cameras 6 , 28 and 29 , images from which are used to calculate the 3d image . fig8 shows a structural diagram of the device ( 3d scanner 30 ) in as side view , including the housing 30 provided with the handle 35 that allows the user to hold the scanner 30 in hand in a comfortable manner . the user can observe the is process of scanning using the display 31 of the scanner 30 . the display 31 of the scanner 30 displays an image captured by the color camera 26 in order for the user to understand which part of the object 16 is in the field of view of the camera 26 , and the image is overlaid with another image of three - dimensional polygonal tries h calculated using the built - in computer 33 on the basis of processed images from cameras 6 , 28 and 29 . this is necessary for the user to understand what part of the object 16 he had measured using the 3d scanner 30 . each polygonal 3 d surface is recorded with the built - in computer 33 in the coordinate system of the object 16 using the icp algorithm . the projector 5 and cameras 6 , 26 , 28 and 29 are rigidly fixed to the optical mount 34 . optical mount 34 should be made of a sufficiently durable material such as aluminum or steel , which has a relatively low coefficient of linear expansion , as preserving the mutual position of the cameras 6 , 26 , 28 and 29 with respect to the projector 5 is very important and influences the accuracy of scanning of surface . this position is measured during the calibration of the device ( scanner 30 ). any small micron - sized movement of the cameras 6 , 26 , 28 , 29 with respect to the projector 5 could lead to distortion of measurements , which are measured in millimeters . during scanning at the stage of recording of strikes in the coordinate system of the object using an icp algorithm , errors resulting from movements of the cameras 6 , 26 , 28 , 29 are summed for each surface , and it can lead to centimeter - sized distortions of measurements of the object 16 . saving and transmission of data can be performed through a connector for connecting external removable storage devices . furthermore , a wireless communication unit from the following group : bluetooth , wi - fi , nfc , provides , if necessary , wireless transmission of data to another computer ( pc ). to carry out the measurements using the proposed method and the scanner 30 , the scanner must be taken into hands , the measured object 16 placed in the field of view of the cameras 6 , 26 , 26 , 29 , so that it can be observed on the screen 31 , as the color image from the camera 26 is immediately ( without processing ) displayed on the display 31 . this is followed by positioning of the measured object 16 at the correct distance from the scanner 30 , i . e . so that it was in the working area 7 . during operation of the scanner 30 , the projector 5 projects the image of the transparency 3 on the object . the camera 6 captures the reflected light and records the image of the illuminated object 16 . then the built - in computer 33 processes the image captured by the camera 6 . if there are any ambiguities or uncertainties in the calculation , then the program uses images obtained from cameras 28 and 29 to improve and check the position of elements of projected image of the transparency 3 . after processing the images from cameras 6 , 26 , 28 , 29 , the computer 33 displays on display 31 a calculated image of a 3d model of the object 16 with the calculated dimensions . if necessary , the user can walk around the object 16 with the scanner 30 in hand , constantly keeping the object 16 m the work area 7 of the scanner 30 and receiving images of the object 16 with different angles or different positions of the scanner relative to the object . computer 33 processes the images obtained from cameras 6 , 28 , 29 at each angle and uses icp algorithm to put new 3d models into the coordinate system of the first 3d model obtained . as the result , the user obtains a 3d model of the object 16 with calculation of its dimensions , i . e . the user receives a 3d measurement of the object 16 from all sides . therefore , the proposed method provides an increased uniformity of the obtained measurement along the y - axis , increased sensitivity along the z - axis , and almost complete elimination of errors , i . e . improving the accuracy of measurements and allowing creation of a single - piece mobile device ( 3d scanner ) for implementation of this method . the present invention is embodied with multipurpose equipment extensively employed by the industry . 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