NCSLI 2007 In House Capability of an Optical CMM Calibration for any Company Shawn Mason Boston Scientific

Purpose This paper will present the in-house development and implementation of a calibration process for calibrating an Optical CMM. This paper will present the in-house development and implementation of a calibration process for calibrating an Optical CMM. Topics covered CMM Background (Types of Dimensional Measurement) CMM Background (Types of Dimensional Measurement) In House Development In House Development Uncertainty Components and a Uncertainty Budget Uncertainty Components and a Uncertainty Budget Calibration Process Calibration Process Issues and Problems (Encountered During the In House Development) Issues and Problems (Encountered During the In House Development) Data Results Data Results Vendor Verses In House Vendor Verses In House Future Improvements Future Improvements Conclusion Conclusion

CMM Background There are three types of measurement technologies that are used to inspect standard geometrical dimensions they are as follows: There are three types of measurement technologies that are used to inspect standard geometrical dimensions they are as follows:Video Touch Probe Laser

CMM Background Each has its own strengths and weaknesses they are listed below: Each has its own strengths and weaknesses they are listed below: Video Touch Probe Laser StrengthsNon-Contact Edge Detection Fast data acquisition of edges General sampling Surface information Internal features Non-Contact Surface information Fast data acquisition of surfaces Weaknesses Features must be able to be imaged by the CMM optics system (grid alignment is critical) Physical contact Slow data acquisition of features Probe Lobbing Errors Performance can be surface dependent (laser alignment is critical)

CMM Background I will be talking about the Motorized Optical Coordinate Measuring Machine, which consists of the following components: I will be talking about the Motorized Optical Coordinate Measuring Machine, which consists of the following components: Motorized zoom lens Motorized zoom lens High resolution color camera High resolution color camera Granite Base Granite Base LED back light, LED ring light, LED lights beneath the stage, Fiber Optic ring light, or a Vector light LED back light, LED ring light, LED lights beneath the stage, Fiber Optic ring light, or a Vector light Coaxial TTL top light Coaxial TTL top light DC Servo motor drive for the Z axis DC Servo motor drive for the Z axis Stepper motor drives for the X, Y axis Stepper motor drives for the X, Y axis Metrology software (analysis and run programs) Metrology software (analysis and run programs)

Optical CMM

In House Development As part of the uncertainty budget process a equipment specification had to be developed As part of the uncertainty budget process a equipment specification had to be developed

In House Development Equipment Specification Item # Desc of T&ME Measurement Type Measurement Range Accuracy 1 Par focalization Focus check (inches) Full range of zoom ± inches 2 Rotational Alignment Pass/Fail Camera FOV Pass/Fail 3 Coaxial Alignment Conecntic alignment check (inches) Full range of zoom ± inches 4 LED Reticle Alignment Pass/Fail Camera FOV Pass/Fail 5 Optics calibration Video to VGA Accucentric FOV, zoom light (all Pass/Fail) Video to VGA Accucentric FOV, zoom light Pass/Fail 6AutofocusAstigmatism(Pass/Fail) Full range of focus Pass/Fail 7 Nonlinear calibration (X,Y stage) Length (inches) 8 x8 (inches) ± inches 8 Nonlinear calibration (Z axis) Length (inches) 2.95 inches max (lens dependent) ± inches

Optical CMM Uncertainty Budget Symbo l Uncertainty SourceTypeLimit ValueUnitsDistributionDivisorSensitivity Coefficient Standard Uncertainty UrCalibration Grid Repeatability A35µinNormal UtceTCE of GridB24.0µinRectangular UtceTCE ErrorB2.4µinRectangular UtThermometerA.60µinNormal UedElastic DeformationBNeglibleN/A µcCombined Uncertainty22.3 UExpanded Uncertainty K= Note: This uncertainty budget does not include the uncertainty for the Z Axis Step Gage Note: This uncertainty budget does not include the uncertainty for the Z Axis Step Gage Ur Certificate of calibration from an accredited lab which is 35uin Ur Certificate of calibration from an accredited lab which is 35uin UtceGlass is 6.0ui/in calibration performed on 72F which is 4F 6.0ui/in x 4 = 24uin UtceGlass is 6.0ui/in calibration performed on 72F which is 4F 6.0ui/in x 4 = 24uin Utce 10% error that is known as uncertainty of nominal differential expansion (UNDE) Utce 10% error that is known as uncertainty of nominal differential expansion (UNDE) Ut Thermistor uncertainty is.1F x 6.0ui/in =.60uin Ut Thermistor uncertainty is.1F x 6.0ui/in =.60uin

Uncertainty Budget Touch Probe CMM

Uncertainty Budget Touch Probe CMM Temp Influence

Calibration Process The calibration process may consist of the following tests: Field of View Field of View Grid Alignment Grid Alignment Nonlinear calibration X,Y Nonlinear calibration X,Y Nonlinear calibration Z Nonlinear calibration Z Par focalization Par focalization Coaxial Alignment Coaxial Alignment Grid Projector Alignment Grid Projector Alignment Rotational Alignment Rotational Alignment Set up machine for production use Set up machine for production use

Calibration Process Field of View Field of View A Video calibration standard is placed on the CMM stage surface and the Optical CMM measures the.02,.04, and.08 diameter at 100x to max magnification. A Video calibration standard is placed on the CMM stage surface and the Optical CMM measures the.02,.04, and.08 diameter at 100x to max magnification. Grid Alignment Grid Alignment The grid is positioned on the CMM stage surface plate in the Y Axis and is aligned in the X Axis through the software program. This alignment will help in reduce any errors in the X, Y Axis measurement. The grid is positioned on the CMM stage surface plate in the Y Axis and is aligned in the X Axis through the software program. This alignment will help in reduce any errors in the X, Y Axis measurement. Nonlinear calibration X, Y Nonlinear calibration X, Y The X & Y coordinates are verified and compared to the coordinates from the Standard calibration certificate values. The X & Y coordinates are verified and compared to the coordinates from the Standard calibration certificate values.

Calibration Process Nonlinear calibration Z Nonlinear calibration Z The Z coordinate is verified and compared to the coordinate from the Standard calibration certificate values. The Z coordinate is verified and compared to the coordinate from the Standard calibration certificate values. Par focalization Par focalization The Alignment Reticle (black dot) is placed on the CMM stage surface plate and the Optical CMM is checked to be in focus from High to Low magnification within a certain Z readout tolerance. The Alignment Reticle (black dot) is placed on the CMM stage surface plate and the Optical CMM is checked to be in focus from High to Low magnification within a certain Z readout tolerance. Coaxial Alignment Coaxial Alignment The Alignment Reticle (black dot) is placed on the CMM stage surface plate and the Optical CMM X & Y is checked via a radius chart to be within a certain tolerance. The Alignment Reticle (black dot) is placed on the CMM stage surface plate and the Optical CMM X & Y is checked via a radius chart to be within a certain tolerance.

Calibration Process Grid Projector Alignment Grid Projector Alignment The Alignment Reticle (square edge) is placed on the CMM stage surface plate and the Optical CMM is checked to be in focus from the edge of the square to the dot pattern within a certain Z readout tolerance. The Alignment Reticle (square edge) is placed on the CMM stage surface plate and the Optical CMM is checked to be in focus from the edge of the square to the dot pattern within a certain Z readout tolerance. Rotational Alignment Rotational Alignment The Alignment Reticle (black dot) is placed on the CMM glass plate on stage or the stage surface and the Optical CMM checks the diameter from ½ from each side within a certain Y tolerance. The Alignment Reticle (black dot) is placed on the CMM glass plate on stage or the stage surface and the Optical CMM checks the diameter from ½ from each side within a certain Y tolerance. Set up machine for production use Set up machine for production use The Alignment Reticle and GRID are removed and the lighting is set back to its normal setting and if necessary a check standard or Gold standard is measured on the Optical CMM before it is released back to production. A check standard or Gold standard can be used as a daily check before each shift. The Alignment Reticle and GRID are removed and the lighting is set back to its normal setting and if necessary a check standard or Gold standard is measured on the Optical CMM before it is released back to production. A check standard or Gold standard can be used as a daily check before each shift.

Issues and Problems during the Development Purchase time for the 8x8 Glass Grid or Z axis step gage Purchase time for the 8x8 Glass Grid or Z axis step gage Research time for an accredited vendor to calibrate the 8x8 Glass Grid or Z axis step gage Research time for an accredited vendor to calibrate the 8x8 Glass Grid or Z axis step gage Calibration time from the vendor Calibration time from the vendor Data analysis time to review the results Data analysis time to review the results Development time to write the calibration process (usually around 20 pages not including adjustment steps) Development time to write the calibration process (usually around 20 pages not including adjustment steps) Resources to calibrate the Optical CMM’s Resources to calibrate the Optical CMM’s

X Axis Initial Results X Axis Initial Results

X Axis Adjusted Results X Axis Adjusted Results

Y Axis Initial Results Y Axis Initial Results

Y Axis Adjusted Results Y Axis Adjusted Results

X Axis Repeatability

Y Axis Repeatability

Vendor vs. In House Typical Calibrations performed by an outside service provider may include the following: Typical Calibrations performed by an outside service provider may include the following: X,Y axis linear calibration X,Y axis linear calibration Z axis linear calibration Z axis linear calibration Par focalization Par focalization Coaxial alignment Coaxial alignment X axis accuracy X axis accuracy Y axis accuracy Y axis accuracy Machine repeatability Machine repeatability Linear accuracy (XY plane) Linear accuracy (XY plane) Linear accuracy (Z axis) Linear accuracy (Z axis) Squareness (Perpendicularity) (XY, YZ, ZX) Squareness (Perpendicularity) (XY, YZ, ZX) Video Probe Video Probe Magnification offset Magnification offset Uncertainty Uncertainty

Vendor vs. In House Vendor Cost Vendor Cost On Site Calibration $495 to $1,500 plus expenses On Site Calibration $495 to $1,500 plus expenses Travel Travel Need to approve calibration supplier Need to approve calibration supplier Not doing all tests (May do X, Y,Z linear accuracy and squareness, but might not do FOV, Par focalization or Alignment checks) Not doing all tests (May do X, Y,Z linear accuracy and squareness, but might not do FOV, Par focalization or Alignment checks) In House Cost In House Cost Calibration Standard (Kit)$1,250 includes initial calibration cost Calibration Standard (Kit)$1,250 includes initial calibration cost Calibration of the standards Calibration of the standards Need to approve supplier Need to approve supplier Make sure that you talk to the outside service supplier for which parameters that you want to be done because each supplier does not do them all. Make sure that you talk to the outside service supplier for which parameters that you want to be done because each supplier does not do them all. When the outside service provider is done make sure you check out the CMM before releasing back to production. When the outside service provider is done make sure you check out the CMM before releasing back to production. In House calibrations can be done as often as needed and you determine which parameters are important to your process requirements. In House calibrations can be done as often as needed and you determine which parameters are important to your process requirements.

Future Improvements Monitor temperature of the 8x8 Glass Grid and Step Gage Monitor temperature of the 8x8 Glass Grid and Step Gage Measurement Assurance Program with at least three other labs Measurement Assurance Program with at least three other labs Purchase a second 8x8 Glass Grid to reduce down time from vendor calibration Purchase a second 8x8 Glass Grid to reduce down time from vendor calibration

Conclusion The X and Y graphs show the short term repeatability of the Optical CMM is about 100 micro inches, which is 50% of the tolerance. This could be attributed to the Alignment of the Grid. The X and Y graphs show the short term repeatability of the Optical CMM is about 100 micro inches, which is 50% of the tolerance. This could be attributed to the Alignment of the Grid. The biggest uncertainty contributor for the CMM was the Calibration Grid Reproducibility. The biggest uncertainty contributor for the CMM was the Calibration Grid Reproducibility. The Calibration Grid Reproducibility standard uncertainty was found to be at 17.5 uin. The Calibration Grid Reproducibility standard uncertainty was found to be at 17.5 uin. The second highest uncertainty contributor for the CMM was the TCE of the Grid. The second highest uncertainty contributor for the CMM was the TCE of the Grid. The TCE of the Grid is 6.0 uin/in °F times the temperature of 72°F which is an estimated standard uncertainty of 13.8 uin. The TCE of the Grid is 6.0 uin/in °F times the temperature of 72°F which is an estimated standard uncertainty of 13.8 uin. The Temperature Glass uncertainty can be reduced by performing the calibration in a controlled environment, monitoring the temperature gradients around the CMM and also monitoring the temperature of the grid and the step gage with a high accuracy thermistor. The Temperature Glass uncertainty can be reduced by performing the calibration in a controlled environment, monitoring the temperature gradients around the CMM and also monitoring the temperature of the grid and the step gage with a high accuracy thermistor.