Triaxial MEMS Gyroscope Research Articles

Design and fabrication of single drive tri-axis MEMS gyroscope

Gyroscopes are sensors that measure the angular rate of an rotating object along one or more coordinate axis. For measuring angular rate along all three axes, usually three different single axis gyroscopes are used. Three sensor systems imply more space and power requirements which are precious commodities in microelectronics. Single-drive tri axis gyroscopes overcome this issue. Owing to their design complications, they have not been explored to the scale of the single axis gyroscopes. In this paper we present a novel design of single drive tri-axis MEMS gyroscope with detail explanation of its working principle. Since gyroscopes are resonant sensors, the natural frequencies of drive and sense modes are expected to be as close to each other as possible to ensure maximum sensitivity. These frequencies depend on the structural dimensions of the design. A design optimization procedure using Finite Element Method (FEM) based parametric modal analysis has been suggested in order to achieve mode matching. An equivalent analytical model is also presented for drive mode and all three sense modes. The optimized design is fabricated using modified silicon on glass bulk micromachining technique. The natural frequencies in drive and sense modes of as fabricated devices were measured and compared with the numerical and analytical values, The experimental values of frequencies are well within 16% of the numerical values. A design upgrade has been suggested to further reduce this error value.

Analysis of the mechanical coupling characteristics of a monolithic tri-axis MEMS gyroscope

The mechanical coupling characteristics of a monolithic tri-axis micro-electromechanical gyroscope have an important effect on the performance of the gyroscope, and the coupling is directly related to the processing error. This paper introduces the structure and principle of a monolithic tri-axis micro-electromechanical gyroscope, establishes a dynamic coupling model, and studies the mechanical coupling problem caused by beam width errors. The finite element analysis tool was used to simulate the harmonic response of the gyroscope structure with beam width error. The driving-to-sensing and sensing-to-sensing coupling characteristics, the equivalent coupling angular rate of the driving mode to each sensing mode, and the cross-coupling coefficients between the sensing modes are investigated. The coupling error under unit beam width error are obtained and can be used as a reference for the structural design of the single-chip tri-axis gyroscope and the precision requirements for processing.

Feasibility of using a novel instrumented human head surrogate to measure helmet, head and brain kinematics and intracranial pressure during multidirectional impact tests

ObjectivesAim of the work is to present the feasibility of using an Instrumented Human Head Surrogate (IHHS-1) during multidirectional impacts while wearing a modern ski helmet. The IHHS-1 is intended to provide reliable and repeatable data for the experimental validation of FE models and for the experimental evaluation of modern helmets designed to enhance the degree of protection against multidirectional impacts. DesignThe new IHHS-1 includes 9 triaxial MEMS accelerometers embedded in a silicone rubber brain, independently molded and presenting lobes separation and cerebellum, placed into an ABS skull filled with surrogate cerebrospinal fluid. A triaxial MEMS gyroscope is placed at the brain center of mass. Intracranial pressure can be detected by eight pressure sensors applied to the skull internal surface along a transversal plane located at the brain center of mass and two at the apex. Additional MEMS sensors positioned over the skull and the helmet allow comparison between outer and inner structure kinematics and surrogate CSF pressure behavior. MethodsThe IHHS-1 was mounted through a Hybrid III neck on a force platform and impacted with a striker connected to a pendulum tower, with the impact energies reaching 24J. Impact locations were aligned with the brain center of mass and located in the back (sagittal axis), right (90° from sagittal axis), back/right (45°), and front right (135°) locations. Following dynamic data were collected: values of the linear accelerations and angular velocities of the brain, skull and helmet; intracranial pressures inside the skull. ResultsDespite the relatively low intensity of impacts (HIC at skull max value 46), the skull rotational actions reached BrIC values of 0.33 and angular accelerations of 5216rad/s2, whereas brain angular acceleration resulted between 1,44 and 2,1 times lower with similar values of BrIC. ConclusionsThe IHHS-1 is a physical head surrogate that can produce repeatable data for the interpretation of inner structures behavior during multidirectional impacts with or without helmets of different characteristics.

Fractional Order Fuzzy Dynamic Backstepping Sliding Mode Controller Design for Triaxial MEMS Gyroscope Based on High-gain and Disturbance Observers

In this paper, a dynamic backstepping sliding mode controller with a fractional order sliding surface, which has a fuzzy boundary layer, is designed based on high-gain and disturbance observers for controlling the performance of a micro-electro-mechanical triaxial gyroscope. To compensate uncertainties of a system, a combination of sliding mode and robust nonlinear backstepping controller is used. In this design, in order to increase the degree of freedom of the controller, the sliding surface is selected to be of fractional order. in this paper, in order to significantly reduce the chattering phenomenon in the control signal, a new dynamic sliding surface in addition to the initial sliding surface and also fuzzy control theory to controllig the boundary layer are used. In addition, a high-gain observer and a disturbance observer are used to estimate the system states and incoming disturbances to the system. The asymptotic stability of the closed-loop system is proven by Lyapunov stability theorem. In order to evaluate the performance of the designed controller, this controller is compared with other sliding mode controllers. Simulation results show that the proposed controller has much less chattering phenomenon in control signal, increasing system stability, reducing the rise time and better tracking.

Extended state observer-based robust non-linear integral dynamic surface control for triaxial MEMS gyroscope

SUMMARYThis paper reports an extended state observer (ESO)-based robust dynamic surface control (DSC) method for triaxial MEMS gyroscope applications. An ESO with non-linear gain function is designed to estimate both velocity and disturbance vectors of the gyroscope dynamics via measured position signals. Using the sector-bounded property of the non-linear gain function, the design of an $\mathcal{L}_2$-robust ESO is phrased as a convex optimization problem in terms of linear matrix inequalities (LMIs). Next, by using the estimated velocity and disturbance, a certainty equivalence tracking controller is designed based on DSC. To achieve an improved robustness and to remove static steady-state tracking errors, new non-linear integral error surfaces are incorporated into the DSC. Based on the energy-to-peak ($\mathcal{L}_2$-$\mathcal{L}_\infty$) performance criterion, a finite number of LMIs are derived to obtain the DSC gains. In order to prevent amplification of the measurement noise in the DSC error dynamics, a multi-objective convex optimization problem, which guarantees a prescribed $\mathcal{L}_2$-$\mathcal{L}_\infty$ performance bound, is considered. Finally, the efficacy of the proposed control method is illustrated by detailed software simulations.

A Novel Tri-Axial MEMS Gyroscope Calibration Method over a Full Temperature Range.

The micro-electro-mechanical inertial measurement unit (MEMS-IMU) has gradually become a research hotspot in the field of mid-low navigation, because of its advantages of low cost, small size, light weight, and low power consumption (CSWap). However, the performance of MEMS-IMUs can be severely degraded when subjected to temperature changes, especially gyroscopes. In order to make full use of the navigation accuracy, this paper proposes an optimized error calibration method for a tri-axial MEMS gyroscope across a full temperature range. First of all, a calibration error model is established which includes package misalignment error, sensor-to-sensor non-orthogonality error, scale factor, and bias. Then, a simple three-position positive/reversed test is undertaken by carrying out a single-axis temperature-controlled turntable at different reference temperature points. Lastly, the error compensation vector is obtained using the least squares method to establish an error matrix. It is worth mentioning that the error compensation vector at a known temperature point can be calculated through Lagrange interpolation; then, the outputs of the tri-axial MEMS gyroscope can be well compensated, eliminating the need for a recalibration step. The experimental results confirm the effectiveness of the proposed method, which is feasible and operational in engineering applications, and has a certain reference value.

Thermal calibration of a tri-axial MEMS gyroscope based on Parameter-Interpolation method

The error of a MEMS gyroscope is highly dependent on the ambient temperature. Traditionally, it is modeled with polynomials, which cannot achieve sufficient accuracy. In order to solve this problem, a Parameter-Interpolation method is proposed to model and calibrate the deterministic error of a MEMS gyroscope. First, the establishment of a MEMS gyroscope's error model and the calibration methods are discussed. Based on the traditional method, we come up with the Parameter-Interpolation (PI) model. Its parameters vary with temperature and each group of parameters is saved separately. The gyroscope is calibrated through interpolation. Then, we design a multi-position experiment test using a thermal turntable to test the traditional and the Parameter-Interpolation (PI) methods. Finally, we process the data collected in the experiments and compare the results of these two methods. Results show that both methods are valid to improve the accuracy of a MEMS gyroscope but the Parameter-Interpolation (PI) method is more effective.

Study on a vibratory tri-axis MEMS gyroscope with single drive and multiple axes angular rate sense

In this paper a vibratory tri-axis gyroscope with single drive and three axes angular rate sense is presented. Firstly the structural design is proposed. And based on the modal analysis of this structure the operating principle of gyroscope is explained. Secondly the detail design of this gyroscope is presented. Based on simulation, the performance of the gyroscope is evaluated, the character of structural coupling among the drive and sense modes is studied. Thirdly the SOI fabrication process for this gyroscope is described. Fourthly the circuitry design including AGC and PLL is discussed, and the signal process is described in detail. Finally the implementation of this gyroscope is presented. Experiment results show the performance of the gyroscope. The scale factors are ?0.0078 V/°/s, ?0.0043 V/°/s and ?0.0049 V/°/s along X-, Y- and Z-axis respectively. And experiment results also indicate the character of structural coupling among the drive and sense modes similar with the results of simulation.

A novel tri-axis MEMS gyroscope with in-plane tetra-pendulum proof masses and enhanced sensitive springs

This paper presents a tri-axis MEMS gyroscope design with novel tetra-pendulum proof masses for X-, Y-axis and regular proof masses for Z-axis rate sensing, which are all coupled with and embedded in a conventional tuning fork driving frame. The four pendulum proof masses are suspended via the torsional springs to a common center anchor and can be driven to swing around the anchor via the tilted transforming springs as the driving frame is oscillated in an anti-phase mode. As an X-, Y-axis angular rate is applied, the tetra-pendulum proof masses will rotate around the torsional springs in pairs for X- and Y-axis differential sensing, respectively. In particular, we investigated the relationship between the tilting angle of the transforming spring and its transforming efficiency, i.e. the amplitude ratio of the pendulum's swing to the driving oscillation, which shows a straight impact on the sensitivity. By theoretical analysis and Ansys simulation, we achieved an optimal tilting angle of 22.5°, which extends along the angular bisector of the pendulum's and driving mass’ moving direction and demonstrates a significant increase in transforming efficiency by about 40%, compared with the trivial tilting angle of 45°. By employing an SOI-based bulk micromachining process, the prototype device with the optimal design of the transforming spring (type I) and that with the trivial design (type II) for reference have been successfully fabricated. As expected, the testing results indicate an increase of more than 20% in the X- and Y- sensitivities, which is mainly from the enhanced sensitive transforming springs.