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Measurement Technologies

Measurement Technologies

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Measurement Technologies

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  1. Measurement Technologies • A wide variety of technologies are available to measure position • Each approach has advantages and limitations • No one approach is dominate, rather, given the state-of-the-art, some are better suited than others for specific applications • With economic and technological changes over time, the “best” solution may change

  2. Previously Covered Technologies • Mechanical Position Tracker • Articulated Arm/CMM • Optical Position Tracker • Laser Based Technologies • Laser or Structured Light Scanning • Time-of-flight Laser Scanning • Laser Tracking • Digital Optical Methods (Krypton) • Photogrammetric Methods

  3. Magnetic Position Tracker • Measurements of the local magnetic field at the sensor • Typically, a field generator produces a electromagnetic field in which a sensor coil can determine its position and orientation • Line of sight not necessary • Ferromagnetic and conductive materials can affect the measurements • Magnetic field strength is inversely proportional to the cube of distance from the source

  4. NDI AURORA† • Primarily used to track surgical instruments • Unaffected by medical-grade metals • Maximum number of sensors: • 8 (5 DOF) or 4 (6 DOF) • Maximum measurement rate: • 40 Hz • Measurement volume: • 500mm x 500mm x 500mm • Measurement accuracy: • Position: varies from 0.9mm to 1.3 mm based on distance from field generator • Orientation: 0.3 † NDI also offers OptoTrak, a DMM which competes with the Metris (Krypton) system.

  5. Acoustic Position Tracker • Measurement of the time-of-flight of sound waves • Ultrasonic (higher frequency) is better for avoiding interference • Accuracy can be affected by wind and uncertainly in the speed of sound which is a function of temperature, humidity, etc. • More tolerant of obstructions than optical methods, but still require a line of sight • Spurious noises, such as the jingling of keys, can cause undesirable performance

  6. Pegasus Mobile NoteTaker • Pegasus Mobile NoteTaker • Used to track a pen and digitize handwriting • Ultrasonic transmission from the tip of the pen • Resolution of 0.01 in. to 0.005 in. • Inexpensive (~$200)

  7. Radio or Microwave Position Tracker • Typically, a measurement of the time-of-flight • Used in radar and airport landing aids • Also used in radio frequency asset tags in warehouses or hospitals • Radiated energy is inversely proportional to the square of distance from the source • Global Positioning System • Measurement Accuracy: 50 ft • Measurement Volume: Earth’s Surface

  8. Inertial Position Tracker • Measurements from a group of accelerometers which are gravity compensated and double-integrated to determine position • Addition of gyroscopes allows measurement of orientation • Available in chip form, compact • Completely internal, no line of sight necessary • Drift is a significant drawback

  9. InterSense NavShoe • Inertial position tracker intended to be installed into a person’s shoe • Drift is reduced by utilizing zero velocity constraints in the portion of the step when the shoe is in contact with the floor and not moving • Accuracy: 0.3% of distance traveled

  10. Hybrid Position Trackers • With the number of technologies available, each with its own advantages and shortcomings, it is natural that hybrid systems, which combine two or more technologies, arise • Metris K-Scan MMD combines laser scanning and optical position tracking for a more versatile measurement system

  11. Other Notable TechnologiesMetris iGPS • Similar to the network of GPS satellites, a network of laser transmitters can be placed around a laboratory for to allow for measurements in a large coordinate space • With multiple transmitters, line of sight become less of an encumbrance • Transmitter range: 2-40 meters • Sensor accuracy: <0.050 mm

  12. Other Notable TechnologiesNintendo Wii Remote • Almost a hybrid position tracker • Incorporates an accelerometer, although not used as an inertial position tracker • Has an optical sensor to determine orientation • Rather than the more common outside-looking-in approach this is a inside-looking-out device