Principle, System, And Characteristics Of A Six Degree-of-freedom Accelerometer

The sensing technology for six degree-of-freedom (DOF) acceleration is one kind of sensing technology for multi-dimensional motions by sensing and measuring the three-DOF linear acceleration and the three-DOF angular acceleration of the spatial motion of a measured object with respect to the reference inertial frame. The potential applications of the sensing technology for six-DOF acceleration can be found in industrial automatic control systems, transportations, robot control systems, navigation equipments, interactive entertainment equipments, medical equipments, and earthquake prediction equipments. Up to now, the existing principles and configurations for sensing the six-DOF acceleration are complex, which results in the dimensional size of the developed six-DOF accelerometers will be large and/or the manufacturing will be difficult. In addition, neither the methods nor the standards for evaluating the sensing performances of six-DOF accelerometers have been deeply investigated, which will restrain the application of six-DOF accelerometers. In this case, exploring new sensing methods for six-DOF acceleration, developing six-DOF accelerometers with simple structure, low cost, and high accuracy, and establishing the methods and standards for evaluating the sensing performances of six-DOF accelerometers are necessary for expediting the sensing technology for six-DOF acceleration.In this dissertation, the sensing principle of a six-DOF accelerometer based on six coplanar sensing elements for single-axis accelerations is proposed and realized, the systematic configuration and sensing characteristics of the six-DOF accelerometer based on the proposed principle are explored. According to the proposed principle, a piezoelectric six-DOF accelerometer based on six coplanar piezoelectric single-axis accelerometers is designed and developed, the sensing equation and sensing error model of the piezoelectric six-DOF accelerometer are established, and the corresponding compensation method and calibration method for the sensing errors are proposed. On these bases, the experimental setups for evaluating the sensing performances of the developed piezoelectric six-DOF accelerometer are established and the developed piezoelectric six-DOF accelerometer is experimentally tested.The major research works and the innovations in this dissertation can be summarized as follows1. The principle and sensing characteristics of a six-DOF accelerometer based on six coplanar sensing elements for single-axis accelerations are proposed and explored, the six-DOF acceleration can be sensed by accessing and decoupling the outputs from the six coplanar sensing elements for single-axis accelerations fixed at the midpoints of six end-to-end edges of a cube by ensuring that the sensing axial direction of one of the six single-axis accelerometers is aligned along one of the cube edges and any three edges of the six end-to-end edges are not in one plane. The corresponding sensing equation for the six-DOF acceleration is established. According to the established sensing equation, the sensing characteristics, including the sensing errors, sensing resolutions, sensing ranges, and operating frequency range, are analyzed.2. The configuration and principle of a piezoelectric six-DOF accelerometer based on coplanar six piezoelectric single-axis accelerometers is explored, the corresponding sensing equation is established, and the corresponding sensing unit of the piezoelectric six-DOF accelerometer to sense the six-DOF acceleration, as well as the signal processing system, are designed and developed. A rapid prototype of the piezoelectric six-DOF accelerometer is developed with the rapid control prototyping (RCP) technique based on a real-time simulation system.3. The sensing errors of the developed piezoelectric six-DOF accelerometer are analyzed, the mathematical model of the sensing errors and the estimation equations of the sensing errors attributable to the alignment errors and the output errors of the six piezoelectric single-axis accelerometers are established. On these bases, the impacts of the alignment errors and the output errors of the six piezoelectric single-axis accelerometers on the sensing errors of the piezoelectric six-DOF accelerameters are explored. The estimation method and the compensation method for the sensing errors of the piezoelectric six-DOF accelerometer are proposed and the mathematical relationship between the ranges of the sensing errors of the piezoelectric six-DOF accelerometer and the ranges of the alignment errors and the output errors of the six piezoelectric single-axis accelerometers is established utilizing the∞-norms of the vector and matrix. The estimation method for the ranges of the sensing errors after compensation is proposed according to the established mathematical relationship.4. The principle for calibrating the piezoelectric six-DOF accelerometer is proposed and the corresponding calibration model is established. The affect of the errors of the acceleration excitations on the calibration results and the optimal range of the frequency of the angular acceleration excitations are analyzed and an estimation method for the calibration error is proposed. 5. The experiment setups for the six-DOF accelerometer are established. The sensing performances and the effects of the calibration and error compensation of the developed rapid prototype of the piezoelectric six-DOF accelerometer are experimentally verified with a six-DOF random vibration excitation, three fixed axis linear vibration excitations, and three fixed axis angular vibration excitations.The research works in this dissertation has established the theoretical foundation for the research and development of the six-DOF accelerometers based on multiple single-axis accelerometers and will be beneficial to evaluating the sensing characteristics of the six-DOF accelerometers.