Changes between Version 2 and Version 3 of ControlSystems/Sensors/OverviewTraining

Timestamp:

Sep 17, 2017, 10:22:15 PM (8 years ago)

Author:

David Albert

Comment:

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ControlSystems/Sensors/OverviewTraining

@@ -26 +26 @@
 
 '''Exercise''': Ask a mentor to help you take apart an old-style mouse (the kind that had a heavy metal ball instead of bright lights underneath).  In these mice, the ball turned two shafts (X and Y directions) that each had an optical rotary encoder attached.  The mouse movement was detected by counting the interruptions of the light beam in each axis.
+=== Distance Sensors ===
+Robots often need to detect the distance between objects including the robot itself and a target.  The most common solution is a distance sensor that emits a beam of sound or light and measures the time it takes for the echo or reflection to come back.
+* Ultrasonic rangefinders [[Image(https://images-na.ssl-images-amazon.com/images/I/51Q7JIujYaL.jpg,15%,right,margin=10)]] work the same way a bat finds its prey: the sensor emits an ultrasonic chirp and then listens for the echo of that chirp bouncing off the nearest surfaces. The distance to the target is
+   {{{ (time_to_receive_echo X speed_of_sound_in_air) / 2 }}}
+Ultrasonic sensors are incredibly inexpensive and can often be purchased for under $1.  However, as with other sensors, ultrasonic range-finding can be challenging; the sound chirp spreads out quickly from the sensor and will bounce off every surface (floor, ceiling, etc.) not just the target.  This limits the range and reliability of the sensor.  [http://www.robot-electronics.co.uk/htm/srf235tech.htm More expensive ultrasonic rangefinders] emit a narrower beam.  Techniques to focus the sound waves are often required for reliable operation; these can vary from a simple cardboard tube (paper dime rolls work well) to [https://en.wikipedia.org/wiki/Ultrasonic_horn exponential horns] and lensing ([https://www.nde-ed.org/EducationResources/CommunityCollege/Ultrasonics/Physics/refractionsnells.htm sound refracting]) techniques.
+* Light Detection and Ranging (LIDAR) [[Image(https://cdn.sparkfun.com//assets/parts/1/1/8/4/9/14032-01.jpg,15%,right, margin=10)]] uses a low-power laser to measure distance to a target in much the same way as the ultrasonic sensor.  However, unlike a sound beam that spreads out quickly from its source, a laser beam maintains a very narrow focus over long distances, reducing unwanted reflections.  Of course lasers have their limitations too including transparent surfaces or surfaces that will deflect rather than reflect the beam.  LIDAR is expensive too (~$150).