Inertial Instrument Calibration Method Based On Error Separation And Suppression Technology

The inertial instruments are the core components of inertial navigation system,and its accuracy directly affects the navigation accuracy.Improving the accuracy of inertial instruments by improving structural design and manufacturing processes has encountered limitations in manufacturing accuracy limits in practice.By testing on the inertial test equipment,the error model of inertial instruments can be calibrated while compensating for the errors of inertial test equipment,which not only improves the calibration accuracy of inertial instruments but also reduces the calibration cost.It is of very important value for engineering application.This paper focuses on how to compensate for and suppress the error of test equipment,and improve the accuracy of inertial instrument test.On the one hand,the error source generated by the test equipment is analyzed and the relationships between the errors of test equipment and the output errors of inertial instrument are expounded.Then the relevant calibration model is established and the equipment errors are separated and automatically compensated.Finally,the influence of equipment errors on the calibration accuracy of inertial instruments is reduced.On the other hand,the calibration method for suppressing the error of test equipment is studied in principle and the corresponding solutions are proposed for the current problems.This paper starts from the two aspects of equipment error compensation and suppression,studies the calibration method of inertial instrument,and improves the test accuracy of inertial navigation system.The calibration method of accelerometers on an indexing table under the gravity field is studied,and the influence of the angular position errors of the indexing table on the calibration precision of accelerometers is analyzed.The angular position errors of the indexing table is introduced into the calibration model of accelerometers,and a calibration method based on two-sequence combinational orthogonal two-accelerometer method is proposed.The angular position errors of the indexing table are separated from the outputs of accelerometers and compensated automatically based on the proposed method,which reduces the effect of the indexing table errors on the calibration precision of accelerometers.Experiments show that this method can effectively separate the angular position error of the indexing table.Furthermore,the calibration method of error model coefficients for four accelerometers installed equal-spacedly is also proposed to improve the calibration precision and to raise measurement efficiency.In order to reduce the influence of the three-axis turntable errors on the calibration accuracy of IMU,the method to suppress errors of three axis turntable in IMU's separated calibration is studied.Based on the working principle of the turntable,the outer,the middle and the inner coordinate systems of the turntable are established,and the error transferring process of the turntable is analyzed.The expressions of the zero position errors,perpendicularities of adjacent axis lines and installation error of three-axis turntable and the outputs of accelerometer and gyro are derived in detail.A separated calibration model considering the turntable errors and IMU errors is established.The model separates the turntable error and the IMU error parameters,thus can suppress the influence of turntable errors on IMU error parameters and improve the calibration accuracy of IMU error parameters.Simulation results show that the calibration model can overcome the dependence of IMU calibration process on the high precision turntable,has the advantage of reducing the calibration cost,and open a new approach for calibrating high-precision inertial instruments with low-cost turntables.The error suppression technology of IMU's norm-observation method is studied.By using norm of the specific force vector output by the accelerometers and the mode of angular velocity vector output by the gyroscope as the observation quantity.This method does not require accurate attitude information provided by turntable,and reduces the need for the accuracy of the turntable.The relationship between IMU error parameters,the norms of specific force vector and the angular velocity vector is established,by performing ellipsoidal fitting based on IMU measurement information,and transforming the calibration of IMU error parameters into the solution of nonlinear equations.In order to ensure the solution uniqueness of the error parameters of IMU,the error parameters of accelerometer and gyro are converted to their respective parameter frames for calibration.Furthermore,the IMU frame is established to solve the problem of calibration parameter frame unification in the norm-observation method.The systematic calibration method of IMU on horizontal three-axis turntable is studied.According to the velocity error equation of strapdown inertial navigation system,the relationship between the turntable errors,IMU's error parameters and velocity error output by IMU is derived.Then two calibration schemes are designed: the scheme of rotating the outer axis 360° and the scheme of rotating outer axis 90°,while the inner axis and the middle axis are in specified positions.The former has the characteristics of reflecting only the accelerometer error parameters in the north component of the velocity observation and only the gyro error parameters in the east component,which effectively avoids the interaction between the calibration errors of the accelerometers' and the gyros' error parameters.The latter decoupled the coupling relations of three groups of installing errors of IMU and successfully identified 21 error parameters,including scale factors,biases and installation errors.Simulation results show that the proposed method improves the calibration accuracy of IMU error parameters,reduces the dependence on the accuracy of the turntable,and restrains the influence of the turntable errors.