Research On Piezoelectric Six-axis Accelerometer Based On Redundant Parallel Mechanism

With the development towards to the high-grade, precise and advanced performance in biomedicine, inertial navigation, robotics, etc., the six-axis accelerometer is needed urgently to simultaneously measure multi-dimensional motion informations of carriers. Now researches on six-axis accelerometer are still at principle exploratory stage at home and abroad, and the technical bottleneck of which is that difficulty of decoupling and complexity of configuration are contrary. According to the above present situation, a piezoelectric six-axis accelerometer based on redundant parallel mechanism with independent intellectual property right of ours is presented. In this thesis, four aspects including configuration design, decoupling algorithm, structural optimization and parameter identification are studied and discussed deeply.A type of 9-SPS redundant parallel mechanism based on tetrahedral configuration is invented, and which is analysed based on modern mechanism theories such as screw theory, topological theory and so on. Results indicate that this new parallel mechanism has many advantages:(1) nonsingular configuration in initial position and initial pose,(2) analytical form of forward kinematics,(3) redundant informations to deal with secondary noise,(4) superior decoupling characteristics,(5) compact and symmetrical topology. In view of these, the proposed redundant parallel mechanism is served as elastic structure; additionally, piezoelectric ceramics are served as sensitive element and pure-slide pair, and flexure spherical hinges are served as spherical pair. According to the above design scheme, a principle prototype of six-axis accelerometer is established, and a physical prototype with low processing cost and mounting accuracy requirement is manufactured.Dynamics equations of six-axis accelerometer are detailedly deduced in configuration-space based on vector mechanics methods and in phase-space based on analytical mechanics methods, respectively. Inspired by the homotopy theory, the problem of high coupling between the input and output in Newton-Euler equation is solved by introducing aided angular velocity. Under the premise of keeping balance of dynamics equations, index-3 issue about Hamilton constrained canonical equation is solved by deriving the implicit orthogonality between attitude quaternion and corresponding generalized momentums. Two types of decoupling algorithm of six-axis accelerometer are constructed, and they both have advantages of high decoupling efficiency and strong adaptability. Taking into account that there are great differences in numerical behavior between these two types of decoupling algorithm, comparative studies are done qualitatively and quantitatively, and the causes of which are analysed. Meanwhile, the selection principles of two decoupling algorithms are obtained.Fundamental frequency and first-order main vibration mode of the elastomer system are calculated synchronously by using the defined structure matrix as multiplier of the iterative computation, which avoids the complex work of solving equations of higher degree in traditional algorithms skillfully and has the advantages of high computational efficiency and strong astringency. The statically indeterminate reverse dynamic equations about sensitivity model are calculated by constructing compatibility equations about redundant constraint, and the conclusion of sensitivity isotropy is gotten. Three theorems about width of error interval are proposed and proved, and error propagation relations about six-axis accelerometer are revealed and quantized based on the theorems. To some extent, the application areas of interval analysis method are expanded. In order to solve the three major issues of multi-objective optimization effectively, a function of comprehensive property is proposed based on the fundamental frequency model, sensitivity model, and error propagation model. Performance atlas of six-axis accelerometer is drawn, which has great reference values of structural optimization and quantitative evaluation.By means of analyzing the formation mechanism of intermediate parameters in decoupling algorithm, dynamics equations of the system can be simplified to linear algebraic equations only with respect to the partial decoupling parameters when the motions of six-axis accelerometer are pure translations or pure rotations with the frequency under thresholds. According to this, four-step method is proposed to identify the 25 decoupling parameters of parallel type six-axis accelerometer. Taking into account the fact that there is no excitation device on the market matching the four-step method, an experimental platform based on double slider-crank mechanisms is designed and processed to provide the external stimulus. Physical prototype of six-axis accelerometer is installed on the physical prototype of experimental platform, and then the experiments controlled by self-developed virtual instrument are done step by step. Experimental results indicate that the maximum relative error after using the identified parameters to decouple the six-axis acceleration reduces a magnitude compared to that of before, which verifies that the proposed four-step method is correct and feasible.At last, the software simulations and prototype tests are done, which testify the rationality of the proposed scheme and the reliability of the kinematics models and dynamics models.This thesis has worked out some key technical problems about development of six-axis accelerometer, which establishes the theoretical foundation for promoting the process of instrumentation and practicality of six-axis accelerometer. Meanwhile, by further extending or modifying, the research results in this thesis can also provide theoretical guidances for designing and analyzing the other types of multi-axis transducer.