Presentation on theme: "Development of a laser slit system in LabView"— Presentation transcript:
1 Development of a laser slit system in LabView Students: Paolo Bellandi Emanuele FerrariCourse: Optical Measurements 2007
2 Objectives Design of a laser slit system, using active triangulation Implementation of the demonstratorLaser line projectorCMOS cameraTriangulation geometryImplementation of the measurement procedures in LabViewMetrological validation of the system
3 System layoutThe camera sensor is positioned at the image plane. The reference systems are (xc, yc, zc), and (u,v). The former is centered at point C; the latter is centered at point O’; it is the central point of the image plane.P e C : exit and input pupils for the projector and the camera respectivelyH and V: sensor size along u and v coordinates; N and M: sensor resolution along u and vf: focal length od the camera lensTwo geometrical parameters. Baseline d and standoff distance L. Their relation is:FW and FH represent the dimension of the Field of View (FOV). FW is the maximum length of the laser stripe.(x,y,z) is the global reference system.
4 Layout in the x,z plane Similar triangles: To calculate the value of FH:
5 Triangulation Since the triangles are similar: In the presence of the object, ray PO is deviated at Po and impinges at position A on the image plane. Point B is the corresponding point on the reference plane.The height of object point Po is evaluated with respect to the reference plane. The deformation induced by the object shape is evaluated as the difference with respect to the undeformed line on the reference plane.Consequently:
7 Parameters evaluation 1 The geometry is:This means :dLfLaserCCDHFWdLfLaserCCDHFWzyxhence:
8 Parameters evaluation 2 Input valuesD = 16 cmL = 9.5 cmH = 768 pixelsV = 576 pixelsPixel Size = 8,48 umFW = circa 6,5 cmEvaluation of parameter fWe have used an objective with f=12mm and a 5mm ring. The corresponding value for FW is 7 cm.
9 Triangulation againRay tracing in the presence of an object
10 Triangulation equations O’P is evaluated from the measure in pixels multiplied by the pixel size. Then:The vallues of angles b and g:eNote thatAnd
11 Triangulation equations Applying the sine theorem to we haveSine triangles are similar andWe get:thenThis is the measurement information we want
12 Detection of the light pattern The centre of gravity of the signal acquired along direction v, for each value of the coordinate u must be calculated.The algorithm is:bc : position of the centre of gravity; lc : gray level of the c-element.The method must be iterated for all the columns in the image.
13 Labview subVi “Calcolo_Baricentri_Sub” (example) Application of algorithmAcquire image and calculate number of rows and number of columns.Overlay of the centres on the imageImage thresholdingThis subVi outputs the vector of the centres of gravity and the corresponding imageFiltering of the input image (preprocessing)
14 Threshold to trim the detection algoritm Front panelLive acquisitionFreeze imageVisualization windowThreshold to trim the detection algoritm
15 Gray level visulatization along a profile line Front panelFreezed imageGray level visulatization along a profile line
16 Front panel New acquisition Save image Save the centres of gravity Evaluation of the measurement information. Triangulation is performed here.Error message if the results are not saved
17 Results Deformed profile Reference profile: Threshold equal to 229. Value measured by the system: 4.72 mmThreshold equal to 229.Reference measurement (caliper used): 4.73 mm
20 Other results (influence of texture and of reflectivity bottonProfilesReference measure (mm)System measure (mm)threshold5.114.611125.153.98474.4621612.8912.99213
21 ConclusionsFor measurement ranges up to 10mm the measurement uncertainty is 0,1mm.The performances can be increased if absolute calibration is performedCamera modelIntrinsic and extrinsic parameters must be estimatedProjection modelThe projection plane must be estimatedThe front panel is user friendly