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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_284</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_283.html">< previous page</a></td> <td id="ebook_previous" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_284</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_285.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 284</font></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">true if the approach in question is attempting to attain the positioning accuracy available by differential carrier-phase techniques. In this section the effect of the lever-arm separation is investigated under two measurement conditions to determine whether the lever-arm separation can be used beneficially in attitude estimation.</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">All the figures in the following two subsections are derived from an error covariance simulation. The error standard deviations immediately before the Kalman filter update are plotted (i.e., <i>a priori</i> error standard deviations). The posterior error standard deviations would naturally be smaller. The simulations assume a local level (geodetic) INS aided by a differential carrier-phase GPS. The integer search process is assumed to have been completed correctly. The Kalman filter performs carrier-phase measurement updates at a 1-Hz rate. The carrier-phase range error standard deviation is assumed to be 0.01 m. The estimate error state includes the nine nominal error states [<i>n, e, h, </i></font><i><font face="Symbol" size="3">u</font><font face="Times New Roman, Times, Serif" size="1"><sub>n</sub></font><font face="Times New Roman, Times, Serif" size="3">, </font><font face="Symbol" size="3">u</font><font face="Times New Roman, Times, Serif" size="1"><sub>e</sub></font><font face="Times New Roman, Times, Serif" size="3">, </font><font face="Symbol" size="3">u</font><font face="Times New Roman, Times, Serif" size="1"><sub>d</sub></font><font face="Times New Roman, Times, Serif" size="3">, </font><font face="Symbol" size="3">r</font><font face="Times New Roman, Times, Serif" size="1"><sub>n</sub></font><font face="Times New Roman, Times, Serif" size="3">, </font><font face="Symbol" size="3">r</font><font face="Times New Roman, Times, Serif" size="1"><sub>e</sub></font><font face="Times New Roman, Times, Serif" size="3">, </font><font face="Symbol" size="3">r</font><font face="Times New Roman, Times, Serif" size="1"><sub>D</sub></font></i><font face="Times New Roman, Times, Serif" size="1"><sub></sub></font><font face="Times New Roman, Times, Serif" size="3">] and three additive gyro and accelerometer error states. Therefore the dimension of the augmented error state is 15.</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">To clearly indicate the effect of the lever arm alone, the simulation trajectory corresponds to a locally level vehicle with no translational velocity. The vehicle is rotated about the vertical axis through the accelerometer origin. Therefore the accelerometers measure [0, 0, -<i>g</i>]. The rotation results in tilt angles of 0掳 and heading defined 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="19d86203c42faee86c75f85d9bd870d1.gif" border="0" alt="0284-01.GIF" width="88" height="17" /></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">where <i>A</i> = 90掳 and <i>f</i> = (2</font><font face="Symbol" size="3"><i>p</i></font><font face="Times New Roman, Times, Serif" size="3">/60) rad/s. The resulting angular rate vector is</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="2bd6f1c618fcf29c0812e07c9d67103e.gif" border="0" alt="0284-02.GIF" width="150" height="17" /></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">7.6.2.1<br />One GPS Antenna</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">The effect of the lever-arm separation will depend on the direction of the offset vector in body frame. If the offset vector is b</font><font face="Times New Roman, Times, Serif" size="2"><sup><i>b</i></sup></font><font face="Times New Roman, Times, Serif" size="3"> = [0, 0, -<i>L</i>] (i.e., the GPS antenna is directly above the IMU), then the INS prediction of the antenna position will be sensitive to tilt and position errors, but insensitive to azimuth errors (i.e., rotation about the offset vector for a nominally level vehicle). If the offset vector (for a nominally level vehicle) has a significant component in the horizontal plane, then the predicted position will be sensitive to azimuth error. Can this sensitivity be used to attain accurate azimuth alignment?</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">By Eq. (6.195), the measurement matrix corresponding to the lever-arm separation is</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="2d56ec3db34b12b364167de5113a6ceb.gif" border="0" alt="0284-03.GIF" width="346" height="19" /></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">where</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="b1c270f149d83b1ad06ebf43b9aeddad.gif" border="0" alt="0284-04.GIF" width="335" height="54" /></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">h is the usual matrix of GPS line-of-sight vectors, and the lever-arm calibration</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></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_283.html">< previous page</a></td> <td id="ebook_next" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_284</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_285.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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