MIT16_07F09_Lec31

MIT16_07F09_Lec31 - Inertial Instruments and Inertial...

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Inertial Instruments and Inertial Navigation Gimbals Gimbals are essentially hinges that allow freedom of rotation about one axis. Gimbals often have superb bearings and motors to help achieve virtually frictionless behavior. Sensors in the bearings provide measurements of gimbal angles. Three gimbals allow freedom of rotation of a vehicle about three axes while a central platform remains stationary with respect to inertial space. Gvros A gyro is a spinning mass with relatively large angular momentum. We know that the rate of change of angular momentum is equal to the applied moment. A- - - H =M 6Itr If no torque is applied then the angular momentum vector remains stationary with respect to inertial space. Gimbals allow a vehicle to rotate ii-eely about a gyro so the gyro spin axis can provide a single axis direction that is stationary with respect to inertial space. Restraining a gyro about an axis perpendicular to the angular momentum vector provides a means for measuring angular velocity with respect to inertial space. This device is called a rate gyro and is a common sensor for aiding in rate stabilization of vehicles (e.g., the D in a PD controller). Inertial Platforms A gyro mounted on a platform can be used as a sensor in a feedback loop to stabilize the platform with respect to inertial space. This is called an inertially stabilized platform. AS we will see, the inertially stabilized platform is an essential element of inertial navigation.
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Applying torque to the gyro causes its spin vector (i.e., angular momentum vector) to move with respect to inertial space. Thus the inertially stabilized platform can be reoriented with respect to inertial space. Accelerometers A second important inertial sensor is the accelerometer. A simplified diagram of an accelerometer is as follows- &--. . .. . ~1 dehic\e CC~ \eVOwr4~r cc.se.
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MIT16_07F09_Lec31 - Inertial Instruments and Inertial...

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