MEMS SoC: observer-based coplanar gyro-free inertial measurement unit

Abstract

This paper presents a novel design of a coplanar gyro-free inertial measurement unit (IMU) that consists of seven to nine single-axis linear accelerometers, and it can be utilized to perform the six DOF measurements for an object in motion. Unlike other gyro-fee IMUs, this design uses redundant accelerometers and state estimation techniques to facilitate the in situ and mass fabrication for the employed accelerometers. The alignment error from positioning accelerometers onto a measurement unit and the fabrication cost of an IMU can greatly be reduced. The outputs of the proposed design are three linear accelerations and three angular velocities. As compared to other gyro-free IMUs, the proposed design uses less integral operation and thus improves its sensing resolution and drifting problem. The sensing resolution of a gyro-free IMU depends on the sensing resolution of the employed accelerometers as well as the size of the measurement unit. Simulation results indicate that the sensing resolution of the proposed design is 2 • s −1 for the angular velocity and 10 µg for the linear acceleration when nine single-axis accelerometers, each with 10 µg sensing resolution, are deployed on a 4 inch diameter disc. Also, thanks to the iterative EKF algorithm, the angle estimation error is within 10 −3 deg at 2 s.

Design, geometry evaluation, and calibration of a gyroscope-free inertial measurement unit

“…The minimum number of accelerometer axes to determine the relative body movement is six [6][7][8][9][10][11][12][13][14]. However, by using six accelerometers only the transversal and the angular acceleration of the body can be determined.…”

“…Mostov et al investigated the suitability of the cube configuration for automotive applications [12]. T. Chen et al proposed a coplanar setup of a GF-IMU detecting the angular and transversal acceleration in [8][9][10]. For such a coplanar configuration the minimum number of sensors is nine [10].…”

Design and analysis of an orientation estimation system using coplanar gyro-free inertial measurement unit and magnetic sensors

“…The way to construct such a gyro-free IMU, using the minimum number of accelerometers, is to employ three accelerometers measuring the acceleration along the direction parallel to the plane surface of the measurement unit (in-plane sensing), and the other three accelerometers measuring the acceleration along the direction perpendicular to the plane surface of the measurement unit (out-of-plane sensing) [7]. The difference between a conventional cube-like gyro-free IMU and coplanar gyro-free IMU is depicted in Fig.…”

“…Therefore, the second approach is often referred to as a gyro-free inertial measurement unit (IMU) [5,6]. When operating as a stand-alone angular velocity sensor, a gyroscope offers a higher sensing accuracy than a gyro-free IMU due to its high sensitivity and no mathematical integral operation required [7]. On the other hand, when operating as one of the sensor components in an orientation estimation system, the performance difference between gyroscopes and gyro-free IMUs is reduced because they only play portion of roles in improving the accuracy of the angle estimation.…”

“…As a consequence, it is not only expensive for the assembly but also susceptible to the alignment error that would deteriorate its sensing accuracy. In previous research [7], the author proposed a novel "coplanar" gyro-free IMU design, in which all the employed accelerometers, in-plane sensing accelerometers and out-of-plane sensing accelerometers, are situated on the same facet of the measurement unit. Current MEMS technology developments [8,9] show that it is possible to simultaneously fabricate the in-plane and out-of-plane sensing accelerometers on a substrate.…”