Dynamics And Performance Calibration Of Reconfigurable Six-Axis Acceleration Sensing Mechanisms

The continuous development of space technology has spawned the development of six-axis acceleration sensors,making the field of six-axis acceleration sensors show a broad application prospect.Due to the strong nonlinear coupling relationship between multi-input and multi-output,compared with the more mature one-axis and three-axis accelerometers,the six-axis accelerometer has essential differences in theory and technology.Its implementation mechanism and potential key core issues are much more complex.The sensing mechanism is the core module of the six-axis acceleration sensor,and its essence is a parallel mechanism.Reconfigurable design gives the mechanism a new feature of variable structure,so the reconfigurable design of the sensing mechanism can improve the environmental adaptability of the six-axis acceleration sensor.In this paper,the reconfigurable six-axis acceleration sensing mechanism is taken as the research object,and its dynamics and performance calibration are studied.The details are as follows:(1)The dynamic model and error compensation algorithm of sensing mechanism are established based on Kane equation.Firstly,according to the relationship between partial velocity,partial angular velocity,active force and inertial force,the generalized active force and generalized inertial force of the six-axis acceleration sensing mechanism are derived.Then,based on the Kane equation,the inverse dynamic equation of the sensing mechanism is established,and the mapping relationship between acceleration and branch force is solved and verified.Then,a "semi-closed-loop" algorithm is constructed to realize real-time compensation of decoupling error,and the effectiveness of error compensation is verified by experiments.The basic idea of the "semi-closed-loop" algorithm is as follows: the first step is to define four state observations based on four types of state feature points;secondly,based on the characteristics of the external vibration signal,the judgment basis of the state feature points is given.The third step is to construct a feedback loop according to the judgment basis.When the intermediate variable is at the state feature point,the real-time error compensation is performed.(2)Based on the metamorphic mass block structure,a reconfigurable six-axis acceleration sensing mechanism is designed.The metamorphic mass block structure includes a central sphere,an arc slider and an angle.The surface of the central sphere is divided into several triangular blocks of the same size by the annular chute.The bottom of the annular chute has an arc groove along the chute surface.Three angles on a triangular block on the surface of the central sphere are removed to form an arc groove to install an arc slider.The angle piece is installed on the arc slider,and the torsion and slip of the angle piece are realized by using the cooperation relationship between the arc slider and the central sphere.Combined with the assembly and disassembly of the branch chain,the geometric reconstruction and topological reconstruction of the sensing mechanism are achieved.Its reconstruction process is similar to the "cube reduction" operation.(3)In the three-axis acceleration scene,the measurement error,singularity,decoupling accuracy and sensitivity of the six-axis acceleration sensing mechanism and the three-axis acceleration sensing mechanism are compared.Firstly,a 2T1 R acceleration sensing mechanism is designed based on the 3-RPR parallel mechanism as a measurement comparison of three-axis acceleration.Then,the inverse dynamic equation of the 2T1 R sensing mechanism is derived according to the Kane equation,and the error compensation algorithm is established for the error accumulation effect of the acceleration decoupling process.Then,based on the relationship between static stiffness and decoupling accuracy,the influence of structural parameters of two kinds of sensing mechanisms on their decoupling accuracy is compared and studied.Finally,the variation of the sensitivity of the two types of sensing mechanisms with structural parameters is compared.(4)A calibration platform of acceleration sensing mechanism is designed and an experimental system is built.By changing the matching relationship between the calibration gear and the calibration rack,the second driven rack and the third driven gear,the first driven rack and the second driven gear,the calibration platform can output four motion modes : wired acceleration and angular acceleration,wired acceleration but no angular acceleration,wireless acceleration but angular acceleration,wireless acceleration and no angular acceleration.ADAMS is used to simulate the motion form provided by the calibration platform,and the force of each branch chain of the four topological configuration perception mechanisms of "6-6","9-3","9-4" and "12-6" is analyzed.The obtained data are fitted to clarify the force relationship between the branches of the sensor when installed on the calibration platform.Solid Works secondary development program based on Visual Basic 6.0 is designed.The calibration platform experimental system is built,including sensor module,data acquisition and processing module.The zero drift of each branch of the sensing mechanism is obtained through experiments,which reduces the measurement error caused by zero drift.(5)The working frequency and sensitivity of the sensing mechanism are studied theoretically.The corresponding calibration experiments are completed,and the single performance optimization and comprehensive performance optimization are carried out.According to the Lagrange equation of the second kind,the undamped free vibration differential equation of the parallel six-axis acceleration sensing mechanism is established,and the fundamental frequency model of the sensing mechanism is established by solving the equation.The two structural parameters(mass block mass and branch stiffness)that affect the fundamental frequency of the sensing mechanism are analyzed,and the internal relationship between the maximum operating frequency and the fundamental frequency is revealed,that is,the fluctuation range of the maximum operating frequency is within the [1/36,1/32] interval of the fundamental frequency.The calibration experiment of working frequency is carried out by using the calibration platform,and the correctness of the theoretical model of maximum working frequency is verified.Combined with the forward dynamic model of the sensing mechanism,the sensitivity of the three topological sensing mechanisms of "6-6","9-3" and "12-6" is analyzed and calculated,and the relationship between their structural parameters and sensitivity is obtained.The correctness of the sensitivity model is verified by the sensitivity calibration experiment.Using the secondary development of ADAMS software,based on the fundamental frequency and sensitivity index,the performance optimization of three topological configurations of "6-6","9-3" and "12-6" was completed.