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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>page_6</title> <link rel="stylesheet" href="reset.css" type="text/css" media="all"> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> </head> <body> <table summary="top nav" border="0" width="100%"> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_5.html">< previous page</a></td> <td id="ebook_previous" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_6</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_7.html">next page ></a></td> </tr> <tr> <td id="ebook_page" align="left" colspan="3" style="background: #ffffff; padding: 20px;"> <table border="0" width="100%" cellpadding="0"><tr><td align="center"> <table border="0" cellpadding="2" cellspacing="0" width="100%"><tr><td align="left"></td> <td align="right"></td> </tr></table></td></tr><tr><td align="left"><p></p><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="right"><font face="Times New Roman, Times, Serif" size="2" color="#FF0000">Page 6</font></td></tr></table><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td align="center"><font face="Times New Roman, Times, Serif" size="3"><img src="4afe5ff922e1f0dc08225165c030ac86.gif" border="0" alt="0006-01.GIF" width="122" height="99" /></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td align="center"><font face="Times New Roman, Times, Serif" size="2">Figure聽1.3<br />Actual聽dead-reckoning聽case.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">worst-case) navigation-system accuracy and the effects of various system errors. For such an analysis, a set of differential equations describing the navigation-system error is useful. The definition of such a set of equations requires assumptions regarding the sensors to be used and the nature of the errors to be analyzed.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">If a magnetic compass is used, then the measured heading contains a time-varying bias due to local magnetic fields (earth or current induced) and the presence of nearby magnetically permeable objects. Therefore the measured magnetic heading is modeled as <img src="b82810c4db5fc252aaae180d4fed8b0e.gif" border="0" alt="C0006-01.GIF" width="79" height="20" /> (see Fig. 1.3). For this example, it is assumed that <img src="9db5975e5c3ed528f064bfcccb39f283.gif" border="0" alt="C0006-02.GIF" width="33" height="13" />, and lateral velocity is not measured. For analysis purposes, this is modeled as <img src="5bfe861083f49b6c2ff108a0615e8a62.gif" border="0" alt="C0006-03.GIF" width="63" height="15" />, where </font><font face="Symbol" size="3">d</font><font face="Times New Roman, Times, Serif" size="3"><i>v </i>= -<i>v</i>. Last, the forward velocity is modeled as <img src="3ba7826a7844fb7ff704a9efcc76b461.gif" border="0" alt="C0006-04.GIF" width="115" height="19" />, which assumes a scale-factor error of </font><font face="Symbol" size="3"><i>d</i></font><i><font face="Times New Roman, Times, Serif" size="3">s</font></i><font face="Times New Roman, Times, Serif" size="3"> and a bias of </font><font face="Symbol" size="3"><i>d</i></font><i><font face="Times New Roman, Times, Serif" size="3">u</font></i><font face="Times New Roman, Times, Serif" size="3">. The actual mechanized system is modeled as</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3"><img src="0a97cad75313d46887f3b02de53c4114.gif" border="0" alt="0006-02.GIF" width="371" height="40" /></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">If any of the instrumentation errors are nonzero, the solution of the ideal and the actual system equations do not coincide once the vehicle is in motion. Since the navigation equations are usually complex enough that closed-form solutions do not exist, alternative analysis techniques are required.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">One valid approach is to perform a linear analysis of the actual system about the ideal system. To perform such an analysis, the assumed form of the actual mechanization equations [i.e., Eq. (1.3)] is subtracted from the ideal equations and linearized with respect to the error variables. This is possible for analysis purposes, even though the actual measurement errors are unknown. More is said on this topic later.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">For the present example, substituting the measurement models into the actual system mechanization equations results in</font><font face="Times New Roman, Times, Serif" size="3" color="#FFFF00"></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3"><img src="19241ffe46a5b121c930f9f406a3591c.gif" border="0" alt="0006-03.GIF" width="479" height="41" /></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr></table><p><font size="0"></font></p>聽 </td> </tr> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_5.html">< previous page</a></td> <td id="ebook_next" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_6</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_7.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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