INS3_ Inertial Navigation Systems _ 4 sensors.ppt
- 1. INS: Inertial Navigation Systems An overview of 4 sensors
- 2. What is an INS? Position (dead reckoning) Orientation (roll, pitch, yaw) Velocities Accelerations
- 3. Sampling of INS Applications Image of an autonomous vehicle Image of a self- balancing personal vehicle
- 4. Accelerometers Image of an airbag
- 5. Accelerometers Proof Mass d1 d2 Fixed fingers Moving finger Suspension Springs F = ma (Newton’s 2nd Law) F = kx (Hooke’s Law)
- 6. Accelerometers Proof Mass d1 d2 Fixed fingers Moving finger Suspension Springs C = ε0A/d (parallel-plate capacitor) ε0 = permitivity constant Voltage Capacitance Surface Area and distance Spring displacement Force Acceleration Integrate to get velocity and displacement Q = CV
- 7. Gyroscopes Image of a bicycle
- 8. Gyroscopes How does it maintain angular orientation? Disk on an axis Disk stationary Disk rotating Red pen indicates applied force
- 9. Gyroscopes – Precession As green force is applied to axis of rotation, red points will attempt to move in blue directions These points rotate and continue to want to move in the same direction causing precession Rotating around red axis, apply a moment around axis coming out of paper on red axis
- 10. Gyroscopes – Gimbaled Rotor Axle wants to keep pointing in the same direction Mounting in a set of gimbals allows us to measure the rotation of the body
- 11. Gyroscopes – MEMS Coriolis effect – “fictitious force” that acts upon a freely moving object as observed from a rotating frame of reference
- 12. Gyroscopes – MEMS Comb drive fingers can be actuated by applying voltage Coriolis effect induces motion based on rotation Capacitive sensors (similar to accelerometers) detect the magnitude of this effect and therefore the rotation Tuning Fork Gyroscope Vibrating Ring Gyroscope
- 13. Fiber Optic Gyroscope (FOG) = attitude rate, 1 = laser light source, 2 = beamsplitter, 3 = wound optical fiber, 4 = photosensor. DSP 4000 turret, antenna, and optical stabilization systems
- 14. GPS – Global Positioning System Constellation 27 satellites in orbit Originally developed by U.S. military Accuracy ~ 10 m 3D Trilateration
- 15. GPS – 2D Trilateration A B C You are here 50 mi 75 mi 30 mi
- 16. GPS – 3D Trilateration Location of at least three satellites (typically 4 or more) Distance between receiver and each of those satellites Psudo-random code is sent via radio waves from satellite and receiver Since speed of radio signal is known, the lag time determines distance
- 17. GPS – Improvements Some sources of error Earth’s atmosphere slows down signal Radio signal can bounce off large objects Misreporting of satellite location Differential GPS (DGPS) Station with known location calculates receiver’s inaccuracy Broadcasts signal correction information Accuracy ~ 10 m
- 18. GPS – Improvements WAAS (Wide Area Augmentation System) Similar to DGPS Geosynchronous Earth Orbiting satellites instead of land based stations Accuracy ~ 3 m Image of a GPS device
- 19. Encoders
- 20. Encoders – Incremental LED Photoemitter Photodetector Encoder disk
- 22. Encoders - Incremental Quadrature (resolution enhancing)
- 23. Encoders - Absolute 4 Bit Example More expensive Resolution = 360° / 2N where N is number of tracks
- 24. Pros and Cons Pros Cons Accelerometer Inexpensive, small Integration drift error Gyroscope Large selection Integration drift error GPS No drift Data at 1 Hz Encoders Inexpensive Slip