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Alternate Method to Certify Grid Plates and Line Scales using a CMM with Chromatic Confocal Sensor verses Traditional Methods. Hexagon Metrology By: JHorwell Sr. Metrologist July 2013. What may I Learn or Why Listen?. - PowerPoint PPT Presentation



Alternate Method to Certify Grid Plates and Line Scales using a CMM with Chromatic Confocal Sensor verses Traditional Methods Hexagon Metrology By: JHorwell Sr. Metrologist July 2013

#What may I Learn or Why Listen?Alternate method for certifying Line Scales

How to apply a white light confocal sensor for edge detection

Difference between displacement and intensity

Density of the data

Selection Criteria2013 NCSLI International Workshop and Symposium#AGENDA01020304Overview of RequirementsBrief HistoryTest PieceResultsError Budget0506Lessons Learned2013 NCSLI International Workshop and Symposium#OverviewTest the ability of a confocal chromatic sensor to find edges

Review existing Hexagon Hardware and firmware to accomplish this task

Compare distance measurements against certified artifact

Determine the feasibility to certify grid plates and glass line scales on a high accuracy CMM with confocal chromatic sensor2013 NCSLI International Workshop and Symposium#HistoryCurrently most line scales are measured on special purpose hardware consisting of an XY stage, Laser Interferometer feed back for position and an optical measuring deviceOthers use comparative techniques from a certified master scale to the scale under testSome have combinations of manual and automatic systemsIn the past some used high accuracy CMM with an image analysis system to certify grid plates2013 NCSLI International Workshop and Symposium#200mm Glass Scale with Chrome Lines

Task is to be able to find the edges with a standard deviation less than 0.09um

Calculate the distances and compare these to a certified value. 2013 NCSLI International Workshop and Symposium#Equipment Selection CriteriaSmall Measurement Uncertainty 0.3 + L/1000Non Contact Sensor AvailabilityStability over timeHardware, Software and Firmware available and capable for finding edges

2013 NCSLI International Workshop and Symposium#Leitz PMM C 12107 Infinity

Measuring Error MPE in [m] according to ISO 10360-2 (2010-6)E0 0.3 + L/1000E150 0.5 + L/1000R0 0.3

Scale Resolution4nm

LSP S4 Probe head with integrated optional Precitec LR Sensor2013 NCSLI International Workshop and Symposium#Precitec LR Sensor Fully Integrated into Leitz PMM C Infinity

Numeric aperture0.66Measuring procedurechromatic confocalMeasurement angle relative to surface 90 40Measuring distance 6.5 mmDiameter of measuring spot 1.4 m2013 NCSLI International Workshop and Symposium#90 degree Sensor

We are continually developing sensors and adaptors for our systemsThe sensor to the right is similar to the sensor we used but can measure the line scales in the vertical direction verses horizontalThe sensor can be manually rotated and our controller can handle more than one sensor on a single system2013 NCSLI International Workshop and Symposium#Overview Glass Line ScalesFind the edges of a Chrome Lines on Glass Line Scales using the Precitec LR Chromatic Confocal Sensor on the Leitz infinity 12107 in RIBuild a reference system on the Glass Scale using tactile probingBuild an alignment system using the Precitec LR SensorMeasure each reference line via 3-pts and constructing an axisIntersect each reference line with the alignment axisCalculate the distance from each line to the zero line and compare with certificate of certificationTest 2-methods for finding the edgeTest alignment stabilityRun repeat test to determine standard deviations2013 NCSLI International Workshop and Symposium#Test Part Glass Line ScaleCertificate of Calibration No 115-01538 by CIPM MRAUncertainty of Measurement: U = 0.10m + L/2000

The distances between the graduations were measured with a photo mask measuring system consisting of a precision x-y bearing table, a two-axis differential plane mirror interferometer and a microscope. The table moves the graduations to the focus of microscope while the interferometer measures its position. The relative position of a graduation within the field of view the microscope is determined by digital image analysis.The scale was cleaned, supported at the Bessel-points (distance 121mm) and measured with the graduation on top using episcopic white light illumination. For each graduation the position of the trailing edge was measured at the height of the collinear alignment marks 2013 NCSLI International Workshop and Symposium#What was missing from the hardware configurationWhile we could find the edge of the lines using traditional analysis by automatically finding extreme points with a standard deviation between 112nm and 250nm using a 30 repeat test. We determined that these values were not as good as we believe our equipment was capable up.Our Firmware Development Group made a flag within our firmware that allowed us to receive the intensity out verses displacement from the Precitec LR Sensor

This was the break thru that we needed to accomplish our task

2013 NCSLI International Workshop and Symposium#Alignment & Fixture Procedure For Glass ScaleThe Glass Scale was place on 3-spherical pins which were near the airy points with 2 at one level and a single pin at the other airy point. 2-posts were used to align the scale along its axis and a single pin for the stop on the zero end plane of the Glass Scale

Tactile alignmentUsing the LSP-S4 probe head and ruby sphere probe we measured a plane on the top and long side and a single point on the end face. This provided us with the rough alignment before we picked the Precitec LR Sensor from our Probe Change RackOptical AlignmentScanned two lines on the top surface of the Glass Scale, constructed a plane and defined the Z-axis spatial vector and alignment from that.We measured 3-points on the line between the 0 and 10mm lines and constructed axisMeasure same on the last line between the 190 and 200mm marksConstructed an axis from these two points which define the rotational portion of our Coordinate systemMeasured 3-points and constructed an axis on the back side of the zero line at 0.5mm from the axis just createdIntersected this zero line axis with the line the defined the rotational portion of our Reference System and this became the X-zero of our Glass Scale2013 NCSLI International Workshop and Symposium#Alignment of Glass Scale using Precitec LR Sensor010190200Found 3-edge points at 0.5mm from zero alignment axis on the 0-position vertical line and built an axis and the intersection of that axis and the zero alignment line created the XY originFound 3-edge points at 0.5mm spacing on each of the 2-horizontal lines and constructed an axis between then which defined the axial alignment2013 NCSLI International Workshop and Symposium#Measurement SequenceWe started our measuring sequence by measuring the Zero Line using 3-points; constructing an axis and intersecting the newly measured axis with the directional axis of our reference system and got a single point for each line measured.We basically stepped and repeated this process until all lines were measuredWe then calculated the distance in X-direction between each line measured and the Zero Line.We repeated this process 10 times2013 NCSLI International Workshop and Symposium#Finding the edgeWhat are some of the issues with finding the real edge and then correlating this to traditional methods.Edge is not perpendicular to the reference planeEdge is not straightDoes back lighting verses top lighting give two different edgesCan we find the same edge as traditional optical systems and measuring microscopes

2013 NCSLI International Workshop and Symposium#Finding extreme points on the edge

Edge Detail

2013 NCSLI International Workshop and Symposium#Summary of Results

2013 NCSLI International Workshop and Symposium#Current procedureThe 3 slides following this show the results from finding the edge of a single chrome line using ScanOnLine with the following point spacing:0.0001 = 10,000pts/mm0.00005 = 20,000pts/mm0.000025 = 40,000pts/mm

I am hoping to have even lower standard deviations that I originally obtain using the Precitec LR sensor on InfinityCurrently I am finding the edge by selecting points based on light intensity of 0.26 to 0.35When I am on the chrome surface I get saturation which is near a value of 12013 NCSLI International Workshop and Symposium#Finding the Edge Alignment Line

Top picture illustrates the edge as seen by the CMM system in redThe blue line is the change in intensity as the system crosses the edgeThe small red points on top of the blue line are the points used to define the edge based on intensity value.

Lower picture shows the measured edge from the CMM in RedThe line in black shows the intensity curve from the Crocodile box. The change in intensity is from glass surface to the silver plated surface

2013 NCSLI International Workshop and Symposium#Density at 10,000pts/mm

Chrome SurfaceIntensity Points SelectedMeasured CurveGlass SurfaceScan Direction2013 NCSLI International Workshop and Symposium#ResultsThe red line represents average value from 10 repeats the certified value. I did not apply temperature compensation at the moment but could and most likely will.The Blue dots represent the results from the 25 runs2013 NCSLI International Workshop and Symposium#Results - numerical

2013 NCSLI International Workshop and Symposium#Still not Satisfied!

Noise reduction algorithm affects the edge detection! 2013 NCSLI International Workshop and Symposium#Raw Data From CMM with out Noise Reduction

2013 NCSLI International Workshop and Symposium#Selection based on Intensity Data Shown has NO Noise Reduction

The points inside this window represents selected data based on intensity:Blue = 0.5 to 0.6 IntensityBlue