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<?php
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$cacheFile="cache/sensors.html";
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if (file_exists($cacheFile)) //we can read this cache file back reduce database load
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{
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   header("Content-Type: text/html");
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   readfile($cacheFile);
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   exit;
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} else {
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   ob_start(); //start buffering so we can cache for future accesses
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}
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?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"><head> 
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                <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"/>        
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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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                <meta name="keywords" content="sonar, ir, sharp, COTS, Scout, feedback, control system, maxbotix"/> 
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<?php include("header.php"); ?>
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                <title>Sensors | ColonyScout.com</title> 
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</head>
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<body bgcolor="#eeeeee"> 
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<div id="general">
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<?php include("nav.php"); ?> 
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        <div id="body">
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                <div id="body-boxes">
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                        <div class="box-row">
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                                <div class="white-top"></div>
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                                <div class="white-body text-box">
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                                        <a href="javascript:;" title="Click to Expand" onmousedown="toggleDiv('sensor');">
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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 &gt;&gt;</em></a>                                        
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                                        </p>
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                                        <div class="hr"></div>
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                                        <div id="sensor">
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                                        <h2>Environment Mapping</h2>
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                                        <img src="/images/sensors_sonar.jpg" style="float:left;margin:0px 10px 10px 0px;">
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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&reg; EZ&trade; 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&trade; 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" style="clear:both;"></div>
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                                        <h2>Cliff Detection</h2>
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                                        <img src="/images/sensors_cliff.jpg" style="float:left;margin:0px 10px 10px 0px;">
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                                        <p>A trio of short range Sharp&reg; 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" style="clear:both;"></div>
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                                        <h2>Odometry &amp; Vehicle Dynamics</h2>
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                                        <img src="/images/sensors_imu.jpg" style="float:left;margin:0px 10px 10px 0px;">
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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 pitch+yaw-rate gyroscope provide detail of the vehicle's motion in three dimensions.
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                                        </p>
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                                        <div class="hr" style="clear:both;"></div>
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                                        <h2>Complementary Sensing</h2>
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                                        <p>The sonar rangefinders are optionally supplemented by short range LED reflectance sensors for close wall 
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                                        following. A sensor on the front bumper provides resolved impact detection for escape manuevers or 
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                                        when manipulating objects.
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                                        </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>Comparison with commercially available robots valued at &lt;$500 USD.</li>
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                                                        <li>PDF: <a href="http://www.maxbotix.com/uploads/Pendulum_Test_Results.pdf">Maxbotix&reg; EZ4&trade; 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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                                        </div>
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                                        </div><!--end 'sensor' collapse-->
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                                </div>
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                                <div class="white-body text-box">
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                                        <a href="javascript:;" title="Click to Expand" onmousedown="toggleDiv('communication');">
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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 &gt;&gt;</em></a>                                                                                
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                                        </span></p>                                
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                                        <div class="hr"></div>
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                                        <div id="communication" style="display:none;">
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                                        <h2>Bearing and Orientation Module (BOM)</h2><br/>
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                                        <img src="images/sensor_BOM.jpg" />
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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&reg; 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&reg; 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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                                        </div>                                        
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                                        </div><!--end 'communication' collapse-->                        
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                                </div>
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                                <div class="white-body text-box">                                
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                                        <div id="bottom-nav">
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                                                <ul id="pagenav">
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                                                        <li class="previous">
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                                                                <a href="<?php echo $nav[$nav_id['sens']-1]; ?></a></li>
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                                                        <li class="next">
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                                                                <a href="<?php echo $nav[$nav_id['sens']+1]; ?></a></li>
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                                                </ul>
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                                        </div>                                        
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                                </div>
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                                <div class="white-bottom"></div>                                
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                        </div>                                
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                </div>        
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        </div> <!--BODY!--> 
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<?php include("footer.php"); ?>
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</div><!--GENERAL!--> 
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</body></html>
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<?php
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$buffer = ob_get_contents();
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ob_end_flush();
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$fp = fopen($cacheFile, "w"); fwrite($fp, $buffer); fclose($fp);
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?>