A nine-axis inertial measurement unit (IMU) that utilizes three-axis angular velocity measurements from rate gyroscopes and six-axis linear acceleration measurements from three two-axis accelerometers is reported. This system can derive linear acceleration, angular acceleration, and angular velocity via simple memoryless matrix operations, and eliminates the requirement for accelerometer installation at the center of mass as in the traditional IMU. An optimal configuration of the system is proposed based on the analysis of rigid body dynamics and matrix theory. In this configuration, the computed angular acceleration is free of the gravity effect as well. Analyses of sensor position and orientation errors are reported. Experimental validation was executed to evaluate the performance of the system.
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