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Copyright 2004 Northrop Grumman Corporation
Control of 3D Measurement
Systems in Shipbuilding
Large Scale Metrology Workshop
July 22, 2004
Ron Hicks
General Foreman
Northrop Grumman Corporation
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Presentation Outline
• Newport News at a Glance
• Current Projects
• Measurement Equipment
• Policies and Procedures
• Measurement Uncertainty
• Conclusion
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Newport News at a Glance
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Largest Private US Shipyard
$2.8 B in Revenues
18,050 Employees
Delivered Over 800 Ships
— 28 Aircraft Carriers
— 53 Nuclear Submarines
Strategically Located across from
Largest US Navy Base
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550 Acres of Manufacturing and
Construction Facilities
— 2 Miles of Waterfront Property
— 7 Dry Docks and 1 Floating
Dock
— 2 Outfitting Berths and 4
Outfitting Piers
Over 4,000 Engineers, Designers,
and Technicians
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Our Products
Virginia Class Submarines
Nimitz Class Aircraft Carriers
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Construction
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3D Systems Employed at Newport News
• Laser Trackers
• Total Stations
• Digital Photogrammetry
• Portable CMM’s
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3D Systems Employed at Newport News
• Laser Trackers
• Total Stations
• Digital Photogrammetry
• Portable CMM’s
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Departmental Statistics
• 180 surveys per month (average)
• 30 man-hours per survey (average)
• 83 supervisory, engineering, technical and
support personnel.
• Work is generally classified as product
compliance, process control, alignment or
reverse engineering.
• Typical tolerances range from ±0.002” - ±0.075”.
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Procedures and Qualifications
• Newport News uses an internal procedure (Q-1022) for control
of Inspection, Measuring and Test Equipment (IM&TE)
• This procedure satisfies the requirements of:
— ANSI/ISO/ASQ Q9001-2000
— MIL-STD-45662A
— MIL-I-45208A
Contractual requirements
— MIL-Q-9858A
• Working to obtain compliance to ANSI/NCSL Z540-1-1994
• ISO 9000 certified quality system
• Licensed by the Department of Energy (DOE) for Navy Nuclear
Work
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Calibration Standards
• Newport News Procedure Q-1022 requires that all
3D Measurement IM&TE be calibrated and
maintain a minimum of a 4:1 accuracy ratio,
traceable to the NIST.
• Vendor calibrations must adhere to the same 4:1
ratio.
• Uncertainty calculations are used to justify
calibration ratios less than 4:1.
• All 3D Measurement Equipment must display the
appropriate labels and tags that indicate their
current calibration status.
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System Calibration
• Laser trackers, theodolites, total stations, and
portable CMM arms are calibrated by the
manufacturer according to their recommendations.
• Digital photogrammetry is a self-calibrating
measurement system. Cameras are periodically
returned to the manufacturer for maintenance,
cleaning and calibration.
• Calibration frequencies are determined by the
department, but typically follow the manufacturers
recommendations.
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System Operational and Cross Checks
• Each system has its own unique operational checks.
• Systems are frequently compared to measurements
made from other higher or comparable accuracy
systems.
• Test ranges are frequently measured and
measurement uncertainty is calculated.
• Reality checks are frequently made to machined
parts.
• Accuracy and scale are checked to calibrated invar
and steel reference bars. These are traceable to
NIST.
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Uncertainty in Measurements
• Each survey requires
— Understanding the capabilities of each
system and the job requirements.
— Simulation of jobs with high accuracy
requirements.
— Actual uncertainty calculations.
— Reference to known values (scale or
reference bars, monuments, ship lines
system)
• 95.46% confidence interval (± 2 Sigma) for
minimum measurement accuracy compared to
the product tolerance.
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Uncertainty Calculations
• Uncertainty or standard error is calculated with
each job.
• Calculations must accommodate multiple
instrument types.
• Higher accuracy jobs are simulated in advance.
• Must calculate uncertainties to comply with
current procedures.
• Requires specialized software to calculate
uncertainties from multiple instrument types and
stations.
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Unified Spatial Metrology Network (USMN)
Laser Tracker Network
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Unified Spatial Metrology Network (USMN)
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Unified Spatial Metrology Network (USMN)
Uncertainty Calculated for
the Survey Network
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Unified Spatial Metrology Network (USMN)
Uncertainty Calculated for
the Survey Network
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Uncertainty Characterization Method
Laser Tracker Network
Field Uncertainty
Checks
Manufactures
Values
Horizontal Angle
(arc seconds)
0.8
0.5
Vertical Angle
(arc seconds)
0.8
0.5
Distance
(inches)
0.0003
0.0015 at 30’
*Values are at 1 sigma
Uncertainty Magnitude: Average = 0.00162”
Scale Bar Delta = 0.0004” (34” scale bar)
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Conclusion
• Calculations for uncertainty must be
made and reported for each survey to
insure performance.
• If the uncertainty is known for the
actual job conditions, adjustments can
be made to meet the overall accuracy
requirements.
— Multiple measurements
— Multiple instrument stations
— Guardbanding techniques
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Questions