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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_10</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_9.html">< previous page</a></td> <td id="ebook_previous" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_10</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_11.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 10</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">by external variables</font><font face="Times New Roman, Times, Serif" size="2"><sup>**</sup></font><font face="Times New Roman, Times, Serif" size="3">. Therefore the system designer can use analytic techniques to study the error performance with a high degree of confidence that the results are accurate in spite of the navigation-system location or operating environment.</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">Observability of the heading and the gyro bias errors from position or velocity assumes that appropriate sensors are available. If such sensors were available and deemed desirable to use, the question of how to optimally use these additional measurements to aid the INS would be of interest. Since the INS is already capable of providing position and velocity estimates, such aiding measurements would not necessarily make the navigation system more robust, since external influences would again be able to affect the navigation accuracy. Instead, such measurements are used, after reasonableness checks, to initialize the INS state, calibrate the INS alignment or biases, or estimate the INS position and velocity (i.e., navigation-state) errors. Such techniques are referred to as <i>INS aiding</i>.</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">In addition to serving the above-stated purposes, state-estimation techniques provide tools for quantifying navigation-system accuracy before constructing the system. Such performance analysis is possible with or without external aiding and allows the system engineer to determine quantitative answers to design questions such as (1) What grade of inertial sensors are required for a given application? (2) How much would the navigation performance change with an additional or alternative form of external aiding? and (3) How should the aiding information be used to adjust the current INS state? State-estimation and the systematic performance-analysis techniques are presented in Chap. 4.</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">Last, an alternative to the stated approach is to mount the accelerometers and gyro on a platform that is actuated within the vehicle. If the actuator is controlled to maintain a null output from the gyro, then this platform, once in operation, would maintain its initial alignment. If this initial alignment coincided with the navigation frame, then double integration of the accelerometer outputs without any calculated transformations would provide the navigation-frame velocity and position. Essentially this would replace one computational integration with a mechanical integration and eliminate the need to transform the measured accelerations between body and navigation frames. The gyro mounted on the mechanized platform may either be less expensive or provide higher accuracy (usually the latter) compared with the strap-down gyro, since it is required to sense a much smaller dynamic range. The former approach is an example of a <i>strap-down INS</i>. The latter approach is an example of a <i>stabilized</i>- or <i>mechanized</i>-platform approach. The tradeoff between the two approaches depends on many factors including (1) cost of sensors, actuation, and computing; (2) size and power of the overall navigation package; and (3) aided and unaided accuracy requirements.</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" width="100%"><tr><td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td> <td colspan="3" height="12"></td> <td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td></tr><tr><td colspan="3" height="1"><table cellpadding="0" cellspacing="0" border="0"><tr><td></td></tr></table></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2"><sup>**</sup>A high dynamic environment can affect inertial sensor performance, but this environmental factor is predictable and under the control of the designer.</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_9.html">< previous page</a></td> <td id="ebook_next" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_10</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_11.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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