Quantifying micron-level robotic movement errors using low coherence interferometry

For a long time robotic arms have proven to be extremely useful tools in production and have started to find more applications in general metrology. Installing a non-contact measurement probe to the end of a robotic arm greatly increases the number of useful measurement configurations, making possible previously impossible measurements, such as scanning the anterior and posterior side of a sample with the same probe and without remounting. Using a robotic arm in metrology applications brings to light movement issues which production use might not ever see. Understanding these issues helps inform the usefulness and accuracy of robotic metrology scans. Separating movement errors from measurement results requires a careful mapping of robotic movements. Comparing programmed robotic movements to a known precision surface provides a method for quantifying movement errors through a scan. We measured the airgap between a low coherence interferometry (LCI) probe mounted to the robotic arm and a precision optical flat. We programmed different movement paths of a 6-axis 946 mm reach robotic arm. The movements ranged from linear to a smooth arcing curvature at near, mid, and far reach locations. Deviations ranged from sub-micron to micron levels from the ideal motion paths. Mapping the measurement locations with minimal positioning errors is essential for our goal of accurate metrology results.