colonymech / docs / www / colonyscout / cache / sensors.html @ f59acf11
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<meta name="description" content="Scout fuses sonar with IR sensors to provide realtime feedback about the robots' environment."/> |
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<!--[if lte IE 7]><link rel="stylesheet" type="text/css" href="/mainIE.css" /><![endif]--> <title>Sensors | ColonyScout.com</title> |
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<a href="index.php"><img src="/images/scout_logo.gif"></a> |
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<a title="Introduction to the Scout robot" href="/intro.php">Introduction</a> |
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<a title="Mechanics of the Colony Scout" href="/mechanics.php">Mechanics</a> |
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<a title="Sensors and Communications" href="/sensors.php">Sensors & Communication</a> |
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<a title="Platform: Software and Hardware" href="/platform.php">Platform</a> |
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<a title="Applications for the Colony Scout" href="/applications.php">Applications</a> |
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<a title="Video of the Scout in Action" href="/gallery.php">Video</a> |
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<h1>Sensor Fusion</h1><img src="images/btn_expand.png" /></a> |
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<p class="description">The Scout sensor suite affords increased situational awareness over comparably |
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priced platforms<span class="super">1</span>. Scout fuses long range sonar with short |
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range IR sensors and LED reflectance sensors to provide realtime feedback about the robots' |
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environment. Commercially available off-the-shelf components were used where possible, |
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selected based on range, accuracy, and repeatability characteristics. |
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<br/><br/><a href="javascript:;" onmousedown="toggleDiv('sensor');"><em>learn more >></em></a> |
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<h2>Environment Mapping</h2> |
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<p>Ultrasonic ranging sweeps 360 degrees around each Scout robot, providing up to 48
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measurements per cycle. A compact stepper motor provides precise and rapid position control. The high resolution and |
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fast scanning speed are appropriate for 2D mapping and navigation.</p>
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<p>The Maxbotix® EZ™ line of sonar rangefinders was chosen for their proven accuracy and |
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long term reliability<span class="super">2</span>. The EZ4 provides the narrowest sensing |
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area of the EZ™ family, allowing higher precision maps to be produced, while still
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providing wide coverage for obstacle detection.</p>
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<div class="hr"></div> |
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<h2>Cliff Detection</h2> |
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<p>A trio of short range Sharp® IR rangefinders provide early warning of sharp drop-offs that |
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could compromise the robot's mission.</p>
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<div class="hr"></div> |
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<h2>Odometry & Vehicle Dynamics</h2> |
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<p>Vehicle position is tracked by quadrature encoders on each wheel resulting in 3mm linear accuracy
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<span class="super">3</span>. A custom IMU (inertial measurement unit) consisting of a 3-axis accelerometer |
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and yaw-rate gyroscope provide detail of the vehicle's motion in three dimensions. |
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</p>
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<h2>Complementary Sensing</h2> |
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<p>The sonar rangefinders are supplemented by short range LED reflectance sensors for close wall
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following. Dual sensors on the front bumper provide resolved impact detection for escape manuevers or |
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when manipulating objects. |
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</p>
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<div id="reference-box"> |
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<ol>
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<li>Comparison with commercially available robots valued at <$500 USD.</li> |
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<li>PDF: <a href="http://www.maxbotix.com/uploads/Pendulum_Test_Results.pdf">Maxbotix® EZ4™ Sensor Testing</a></li> |
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<li>48 clicks per revolution, 42mm diameter wheel. (42mm*pi)/48=2.7488mm</li> |
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</ol>
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<h1>Communications</h1><img src="images/btn_expand.png" /></a> |
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<p><span class="description">Scout communicates over several protocols, providing a robust interface |
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over long distances. Inter-robot communications and control commands are broadcast over a self organizing |
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high bandwidth mesh network. The robots also broadcast over IR (infrared light) for localization. |
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<br/><br/><a href="javascript:;" onmousedown="toggleDiv('communication');"><em>learn more >></em></a> |
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<h2>Bearing and Orientation Module (BOM)</h2><br/> |
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<img src="images/irreceiver.gif" /> |
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<p>The Scout BOM provides relative localization information between robots. Four IR transmitters
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around the base broadcast the robot's identification code and the sensor position, allowing |
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relative orientation to be determined. The hardware is specially designed to reject environmental |
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interference such as noise from fluorescent lights and other source of stray IR. |
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The high refresh rate and robust communication permits tighter precision formation control over |
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distances up to 12 feet.</p>
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<div class="hr"></div> |
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<h2>Wireless Network</h2> |
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<p>Inter-robot communications are handled over a 2.4GHz Zigbee® network using the IPv6 protocol. |
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A transfer rate of up to 2Mbps can be achieved over a distance of nearly one mile line-of-sight |
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<span class="super">1</span>. The system uses a true layer 3 mesh network, distributing data |
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packets intelligently amongst the robots. The nature of the mesh network is dynamically |
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robust, self healing after the loss of any communications node.</p>
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<div class="hr"></div> |
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<h2>Wifi Bridge</h2> |
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<p>An optional network bridge can link the 802.15 Zigbee® radio to standard internet |
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enabled devices (802.11b/g). When using this bridge each Scout can be accessed wirelessly over |
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the internet.</p>
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<div class="hr"></div> |
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<div id="reference-box"> |
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<ol>
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<li>PDF: <a href="http://www.atmel.com/dyn/resources/prod_documents/doc8111.pdf">802.15.4 Zigbee Radio</a></li> |
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</ol>
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