Advanced Dimensional Measurement in bullet points

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Method of measurement:

Contact (point-based systems)

    • Coordinate Measurement Machine
      • (+) High accuracy measurement
      • (+) Good for measurement of geometrical features:
      • Diameter of Holes
      • Diameter of Pins
      • Cylindricity
      • Roundness
      • Coaxiality
      • Concentricity
      • (-) Restricted measurement area
      • (-) Operated under temperature-controlled environment
      • (-) Component to be measured must be allowed to be stabilized at that temperature
      • (-) Access to certain features may cause problem
      • (-) Speed of measurement – cycle time due to reposition
      • (-) Less points for calculation of edge detection (done through intersection of planes and other features)
    • Articulated Arm
      • (+) Ideal for gauging
      • (+) User friendly
      • (+) Portability
      • (+) Good for industrial shop floor application
      • (+) Good for measurement of geometrical features:
      • Diameter of Holes
      • Diameter of Pins
      • Cylindricity
      • Roundness
      • Coaxiality
      • Concentricity
      • (-) Restricted measurement area
      • (-) Manual operation
      • (-) Speed of measurement
      • (-) Less points for calculation of edge detection (done through intersection of planes and other features)

 

  • Non-contact
      • Optical method – (Based on image processing, using backlight, direct light, and ring light)
        • (+) Infinite number of points – edges are detected directly
        • (+) Acceptable accuracy
        • (+) Speed of measurement:
          • one picture one measurement
          • feature recognition
          • ideal for real time statistical analysis such as SPC
        • (+) Good for parts with small features
        • (-) Good for measurement of flat parts only where parts can be measured in silhouette
        • (-) Sensitive on dirt and dust, parts need to be clean before measurement
        • (-) Hard to measure low contrast parts such as dark or white parts as well reflective surfaces 

 

      • Laser scanning (Stripe based systems)
        • (+) creates number of point clouds at one scan
        • (+) no contact = no deformation on elastic parts like at contact method
        • (+) good for clay models
        • (-) point clouds must be patched together to create representation of an object
        • (-) some materials absorb or in a way laser goes under surface, and measure surface underneath it, generating misleading results
        • (-) Humidity affects performance
        • Handheld:
        • (+) good for scanning long parts
        • (+) portability
        • Mounted on CMM:
        • Mounted on Articulated Arm:
        • (-) for long parts the station needs to be moved

 

      • White light scanning (Area based systems)
        • (+) Size of the area (up to several metres) scanned at once
        • (+) Good for scanning small objects
        • (+) Robustness and Portability makes the ideal for most demanding environments
        • (-) Presence of holes can be problem, where is need on depth and shape

References:

[1] https://www.develop3d.com/reverse-engineering/a-guide-to-3d-measurement-technologies

[2] Understanding Optical Measurement Quality Digest / April 2009 (p.32 – p.35)

 

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