Academic literature on the topic 'Dual mass electrostatic vibratory gyroscope'

The influence of Casimir and van der Waals forces on the instability of vibratory micro and nano-bridge gyroscopes with proof mass attached to its midpoint is studied. The gyroscope subjected to the base rotation, Casimir and van der Waals attractions is actuated and detected by electrostatic methods. The system has two coupled bending motions actuated by the electrostatic and Coriolis forces. First a system of nonlinear equations for the flexural-flexural deflection of beam gyroscopes is derived using the extended Hamilton's principle. In modeling, the nonlinearities due to mid-plane stretching, electrostatic forces, including fringing field, Casimir and van der Waals attractions, are considered. The method of homotopy perturbation is used to solve the equations of equilibrium, with the solution validated by numerical methods. In addition, the effect of nondimensional parameters on the instability and deflection of the gyroscope is investigated. The data presented can be used in the design of vibratory micro/nano gyroscopes.

The micro-electro-mechanical systems (MEMS)-based sensor technologies are considered to be the enabling factor for the future development of smart sensing applications, mainly due to their small size, low power consumption and relatively low cost. This paper presents a new structurally and thermally stable design of a resonant mode-matched electrostatic z-axis MEMS gyroscope considering the foundry constraints of relatively low cost and commercially available silicon-on-insulator multi-user MEMS processes (SOIMUMPs) microfabrication process. The novelty of the proposed MEMS gyroscope design lies in the implementation of two separate masses for the drive and sense axis using a unique mechanical spring configuration that allows minimizing the cross-axis coupling between the drive and sense modes. For frequency mismatch compensation between the drive and sense modes due to foundry process uncertainties and gyroscope operating temperature variations, a comb-drive-based electrostatic tuning is implemented in the proposed design. The performance of the MEMS gyroscope design is verified through a detailed coupled-field electric-structural-thermal finite element method (FEM)-based analysis.

Frequency tuning of work modes in the silicon vibratory gyroscope is studied by the theoretical, numerical, and experimental methods in this paper. First, the schematic structure and simplified kinematics model of the gyroscope were presented for deducing the natural frequencies. Then, the width and length of support beams were optimized to tune work frequencies at their designed value. Besides, the frequency difference was experimentally tested and manually tuned by varying the voltage applied on the tuning capacitors. The test on a prototype showed that the difference could be localized between −55.8 Hz and 160.2 Hz when the tuning voltage limit is 20 V. Finally, a frequency control loop was developed to automatically tune the sense frequency toward the drive frequency. Both the theoretical analysis and numeric simulation show that the difference is stabilized at 0.8 Hz when no Coriolis force or quadrature coupling force is applied. It is proved that the frequency difference is successfully tuned by modifying the size of support beams before fabrication as well as the voltage applied on the tuning capacitors after fabrication. The automatic tuning loop, used to match the work modes, is beneficial to enhance the performance of the gyroscope as well as its resistance to environment disturbances.

A novel three-dimensional (3D) wafer-level sandwich packaging technology is here applied in the dual mass MEMS butterfly vibratory gyroscope (BFVG) to achieve ultra-high Q factor. A GIS (glass in silicon) composite substrate with glass as the main body and low-resistance silicon column as the vertical lead is processed by glass reflow technology, which effectively avoids air leakage caused by thermal stress mismatch. Sputter getter material is used on the glass cap to further improve the vacuum degree. The Silicon-On-Insulator (SOI) gyroscope structure is sandwiched between the composite substrate and glass cap to realize vertical electrical interconnection by high-vacuum anodic bonding. The Q factors of drive and sense modes in BFVG measured by the self-developed double closed-loop circuit system are significantly improved to 8.628 times and 2.779 times higher than those of the traditional ceramic shell package. The experimental results of the processed gyroscope also demonstrate a high resolution of 0.1°/s, the scale factor of 1.302 mV/(°/s), and nonlinearity of 558 ppm in the full-scale range of ±1800°/s. By calculating the Allen variance, we obtained the angular random walk (ARW) of 1.281°/√h and low bias instability (BI) of 9.789°/h. The process error makes the actual drive and sense frequency of the gyroscope deviate by 8.989% and 5.367% compared with the simulation.

A novel silicon based dual-mass vibrating tuning fork vibratory gyroscope (TFG) with differential capacitor structure is designed in this paper. the U-shaped beam is adapted to connecting the two decoupling movement of the framework structure in order to achieve the independent of the movement of drive direction and sense direction. The TFG structure is also optimized to further reduce the mechanical coupling of the device. The drive combs are designed on the mass, while the sense combs are designed on the frame. All the combs in this gyroscope are dominated by slide-film air damping in order to lower the air damping. This gyroscope is designed to obtain robust operation against variations under atmospheric pressure condition. The TFG is tested at atmospheric pressure with a sensitivity of 17.8mV/◦/s and a linearity of 99.989%, capacitance structure sensitivity is 21.5αf/◦/s with an equivalent noise angular rate of 0.028◦/s/Hz1/2, respective.

This paper reports a new dual mass vibratory MEMS z-axis rate gyroscope architecture that prioritizes the sense-mode quality factor and provides improved ordering of the mechanical vibrational modes. The proposed linearly coupled, dynamically balanced anti-phase sense-mode design minimizes substrate energy dissipation to maximize the quality factor. The levered drive-mode mechanism structurally forces the anti-phase drive-mode motion of the symmetrically decoupled tines eliminating the lower frequency spurious mode and providing true mechanical rejection of external shocks and accelerations. SOI prototypes were characterized in a vacuum chamber demonstrating drive-mode quality factor of 67,000 and ultra-high sense-mode quality factor of 125,000. A vacuum packaging technology was introduced and demonstrated a ceramic package-level sealed gyroscope with a quality factor on the order of 100,000. The high quality factor and mode ordering of the new design provide a path toward ultra-high scale factor without compromising the sensitivity to external accelerations.

In this paper, an online compensation method of phase delay error based on a Phase-Frequency (P-F) characteristic has been proposed for MEMS Coriolis Vibratory Gyroscopes (CVGs). At first, the influences of phase delay were investigated in the drive and sense mode. The frequency response was acquired in the digital control system by collecting the demodulation value of drive displacement, which verified the existence and influence of the phase delay. In addition, based on the P-F characteristic, that is, when the phase shift of the nonresonant drive force through the resonator is almost 0° or 180°, the phase delay of the gyroscope is measured online by injecting a nonresonant reference signal into the drive-mode dynamics. After that, the phase delay is self-corrected by adjusting the demodulation phase angle without affecting the normal operation of the gyroscopes. The approach was validated with an MEMS dual-mass vibratory gyroscope under double-loop force-to-rebalance (in-phase FTR and quadrature FTR) closed-loop detection mode and implemented with FPGA. The measurement results showed that this scheme can detect and compensate phase delay to effectively eliminate the effect of the quadrature error. This technique reduces the zero rate output (ZRO) from −0.71°/s to −0.21°/s and bias stability (BS) from 23.30°/h to 4.49°/h, respectively. The temperature sensitivity of bias output from −20 °C to 40 °C has reached 0.003 °/s/°C.

Gyroscopes sense angular speed of the body on which they are mounted. Traditional mechanical gyroscopes are big, bulky, expensive, and hence limited to a few applications. With the advent of Micro-Electro-Mechanical Systems (MEMS), the size and cost of gyroscopes have reduced by orders of magnitude, which has led to their deployment on systems that traditionally did not employ inertial units. Today, Internet of Moving Things (IoMT), automobiles, and consumer electronics gadgets such as cell phones, pads, laptops, gaming consoles, etc., use MEMS accelerometers and gyroscopes. Despite their commercial deployment and success, MEMS accelerometer and gyroscopes remain an active area of research and development because of their growing potential of applications and newer technologies for increasing their functionality and reducing their cost. This work focuses on the complete design, fabrication, device level packaging, and characterization of two different types of MEMS gyroscopes|a dual mass electrostatic vibratory gyroscope and an electromagnetic ring gyroscope. We start by establishing a closed-form mathematical expression for gyroscope sensitivity relating to different design parameters. From the analysis, we present a case study on the effect of mismatch between the actuation frequency and the drive resonant frequency on the sensitivity of the gyroscope. Towards fabrication of MEMS electrostatic gyroscopes, we discuss several fabrication challenges involved in using the traditional SOI-on-glass method. Particularly, the alignment and residual stress issues are discussed in detail. Subsequently, we describe a modified SOI-on-glass fabrication method that success-fully overcomes these issues. A novel hybrid wafer bonding method is presented in conjunction with the modi ed SOI-on-glass process. The proposed process flow is demonstrated by realizing several capacitive MEMS structures. Subsequently, the fabricated devices are characterized for their electrical and mechanical responses showing negligible process-induced stresses. Further, we characterize some of the test-structures for their dynamic response under different ambient pressures. We report on the resonant frequency modulation of inertial MEMS structures due to squeeze lm stiffness over a range of working pressures. We show with experimental measurements and analytical calculations how the pressure-dependent air springs (squeeze lm stiffness) change the resonant frequency of an inertial MEMS structure by as much as five times. A detailed experimental methodology is discussed for finding static stiffness using AFM (Atomic Force Microscopy). Further, dynamic measurements are presented using a non-contact Laser Doppler Vibrometer under varying pressures. The experimental observations are compared with theoretical and FEM models. Finally, we implement the proposed SOI-on-glass fabrication method to fabricate a dual mass, single-axis, folded tuning fork, electrostatic gyroscope. We rigorously characterize the gyroscope structures for their electrical and mechanical response at the die level. We have also developed a drive and sense pre-amplifier circuit for electrostatic gyroscopes. Thus-fabricated gyroscopes have been packaged, and characterized at the device level with rates of rotation from 1 /s to 35 /s, giving a rate sensitivity of 60 V/ /s with a linearity of 99.9%. In a parallel development, we have also fabricated an electromagnetic ring gyroscope that exploits the inherent symmetry of the ring structure and uses relatively low voltage to produce sufficient electromagnetic force for actuation. The electromagnetic ring gyroscope realized in this work requires very thin Al electrical tracks on a suspended ring structure of Si and on the suspensions for electromagnetic actuation and sensing. The process innovation implemented here is a single wafer process with a patented technique (arising from this work) for electromigration preventive layer. The gyroscope thus fabricated has been packaged and characterized giving a sensitivity of 0.04 V/ /s. Although there is a fair amount of modelling and analysis presented in this thesis, the emphasis here is not on such analysis but on physical realization of the gyroscope. Consequently most of the innovations in this work are in fabrication processes and methods. The actual realization of an electrostatic gyroscope is a challenging task, particularly, in a university fab. We have been able to successfully fabricate and test two types of gyroscopes. The entire fabrication and characterization reported in this work has been carried out at the National Nano Fabrication Centre, Micro Nano Characterization Facility of the Centre for Nano Science and Engineering, IISc.
NPMASS

Abstract In this paper we describe a high amplitude electrostatic drive for surface micromachined mechanical oscillators that may be suitable for vibratory gyroscopes. It is an advanced design of a previously reported dual mass oscillator (Dyck, et. al., 1999). The structure is a 2 degree-of-freedom, parallel-plate driven motion amplifier, termed the secondary mass drive oscillator (SMD oscillator). During each cycle the device contacts the drive plates, generating large electrostatic forces. Peak-to-peak amplitudes of 54 μm have been obtained by operating the structure in air with an applied voltage of 11 V. We describe the structure, present the analysis and design equations, and show recent results that have been obtained, including frequency response data, power dissipation, and out-of-plane motion.

Vibratory Micromachined gyroscopes use suspending mechanical parts to measure rotation. They have no gyratory component that require bearings, and for this reason they can be easily miniaturized and batch production using micromachining methods. They operate based on the energy interchange between two modes of structural vibration. The objective of this paper is to study the oscillatory behavior of an electrostatically actuated vibrating microcantilever gyroscope with proof mass at its end. In the modelling, the effects of different nonlinearities, fringing field and base rotation are considered. The microgyroscope is subjected to coupled bending oscillations around the static deflection which are coupled by base rotation. The primary oscillation is generated in drive direction of microgyroscope by applying a pair of DC and AC voltages in the tip mass. Secondary oscillation in sense direction is induced by Coriolis coupling when the beam has the input angular rate along longitudinal axis. Input angular rotation can be measured by sensing oscillation tuned by another DC voltage applied to the proof mass. First a system of nonlinear equations which describes flexural-flexural motion of electrostatically actuated microbeam gyroscopes under input rotation, is derived by extended Hamilton principle. The oscillatory behavior of microgyroscopes is then analytically investigated, where the microgyroscopes are predeformed by DC voltages in both directions. The effects of the nondimensional parameters on the natural frequencies of the system are discussed at the end of the paper.