Woon-Tahk Sung

On the Mode-Matched Control of MEMS Vibratory Gyroscope via Phase-Domain Analysis and Design

This paper investigates a novel method for the mode-matched control of a microelectromechanical systems (MEMS) vibratory gyroscope through a phase-domain analysis. Compared with the previous works, the proposed method presents a simple and robust automatic mode tuning scheme for sensitivity enhancement. In designing the mode-matched control loop, the resonant characteristics of the driving axis are used as the reference mode. Then, the phase difference between sense and drive modes at the resonant frequency of drive mode is used to generate a control signal for phase error regulation. For the control loop design, a linear phase-locked loop is adapted. Through the simulation using practical MEMS gyroscope parameters, the mode-matching performance and robustness of the designed control loop is demonstrated. It is also shown that coupling effect yields no degradation of output sensitivity. Finally, the experimental results obtained by implementing the electronics of mode-matched control verify the feasibility of the proposed method.

Design and performance test of a MEMS vibratory gyroscope with a novel AGC force rebalance control

In this paper, the development and performance test results of a laterally oscillating MEMS gyroscope using a novel force rebalance control strategy are presented. The micromachined structure and electrodes are fabricated using the deep reactive ion etching (DRIE) and anodic wafer bonding process. The high quality factor required for the resonance-based sensor is achieved using a vacuum-sealed device package. A systematic design approach of the force rebalance control is applied via a modified automatic gain control (AGC) method. The rebalance control design takes advantages of a novel AGC loop modification, which allows the approximation of the systems dynamics into a simple linear form. Using the proposed modification of AGC and the rebalance strategy that maintains a biased oscillation, a number of performance improvements including bandwidth extension and widened operating range were observed to be achieved. Finally, the experimental results of the gyroscopes practical application verify the feasibility and performance of the developed sensor.

Development of a lateral velocity-controlled MEMS vibratory gyroscope and its performance test

The objective of this paper is to present a velocity-controlled vibratory MEMS gyroscope that achieves consistent output characteristics in the lateral driving dynamics of the system. Through a systematic automatic gain control loop design process, the driving mode dynamics of the gyroscope is first transformed to take account of the velocity envelope; a reference tracking integral control is then employed. For stabilized loop construction, a mathematical development and stability analysis of the feedback loop is presented, which is followed by numerical simulation using practical sensor parameters. The mechanical structure was fabricated using the conventional deep reactive ion etching process and the anodic wafer bonding method. Vacuum-packaged devices were used for the resonant gyroscope operation. An essential fabrication process for realizing the electrical connection through a thick glass substrate was possible by applying a sandblasting process and spin coating process of conductive epoxy. Finally, loop simulation and experimental results verified that the amplitude-controlled property in the driving loop is preserved under the system parameter variation which resulted in enhanced gyroscope output performance in comparison with other driving schemes.

Design And Fabrication of Anautomatic Mode Controlled Vibratory Gyroscope

In this paper, we present a new approach for performance enhancement of MEMS vibratory gyroscope by means of automatic mode control scheme. The suggested method automatically tunes resonant frequencies of two lateral modes to be identically matched. This draws sensitivity improvement of the sensor and removes manual tuning effort, which are desirable features to achieve a high performance for the mass productive sensor like vibratory gyroscopes. In this paper, we designed and fabricated an electrostatically tunable gyro structure of parallel-type sensing electrodes and automatic mode tuning circuit that utilizes a PLL-based two self-oscillation loops for both driving and sensing mode.

Design and performance analysis of PLL based self oscillation loop in vibrating gyroscope

A self oscillation loop in vibrating gyroscope based on the phase locked loop (PLL) was proposed and a phase error in the PLL was analyzed. The self oscillation loop is a nonlinear feedback loop, which keeps a self-generated and sustained oscillation. In vibrating type gyroscope, a structure needs a driving oscillation at resonant frequency, which is provided by the self oscillation loop. In order to sustain the loop to be stable oscillation and to operate at the precise resonant frequency of the gyroscope, phase locking condition is essentially needed. Phase locked loop is a suitable component for such a purpose. In oscillation loop, PLL provides exact phase shift to oscillate at the resonant frequency point over wide frequency range. However, the performance of the PLL is affected by certain condition of the circuit, e.g. phase error due to the variation of the component values and noise-sensitive features. This directly leads the performance degradation of the gyroscope. Therefore, phase error analysis of PLL was performed and the robust phase shifting circuit was newly suggested. The experiments were accomplished to verify the suggested method.

Automatic mode matching control loop design and its application to the mode matched MEMS gyroscope

In this paper, a mode matching control loop is suggested for the matching of the resonant frequency of the sensing mode with that of the driving mode. Matching of two modes is critical issue of the MEMS vibratory gyroscope to achieve the high sensitivity of the sensor. A new mode matching control loop using the concept of phase locked loop (PLL) is proposed and analyzed. Through the computer simulation using MATLAB and experiments using a real MEMS gyroscope, it is verified that the proposed control loop design matches those two modes and correspondingly improves the sensitivity of a gyroscope.

PD controller design for Micro Gyroscope and Its Performance Test

This paper presents a performance improvement result with the aid of closed feedback controller loop to a micro gyroscope. The dynamic model of a micro gyroscope is derived and a conventional proportional and derivative controller is designed via frequency domain analysis. The proposed control loop is implemented using several analog devices and applied to the SNU-Bosch MEMS gyroscope to check its performance improvement in real environment. The experiments demonstrated the performance improvement with the proposed feedback control loop. The bandwidth, linearity, and bias stability are improved to 78 Hz, 0.504 %, and 0.043 deg/sec, respectively, from 35 Hz, 2.07 %, and 0.066 deg/sec of open loop system.

Vibratory gyroscope controller design via modified automatic gain control configuration

In this paper, a new design approach of force rebalance loop is investigated for the vibratory rate sensor application. The proposed rebalance loop design takes advantages of a modified AGC loop configuration to simplify the system dynamics of oscillating characteristics. The proposed modification of AGC and rebalance strategy, which maintains controlled oscillation in the loop, acquires several advantages. First, it is possible to analyze and design the transient dynamics using a classical linear control theory. Also the control system to achieve the design objective is implemented using a relatively simple feedback loop. The practical application to vibratory gyroscope has shown that the force rebalance control with the proposed AGC configuration meets the design objective well from simulation results. Experiment is expected to verify the feasibility and performance of the proposed control scheme.

Design of an AGC driving loop in MEMS gyroscopes

Abstract This paper presents a new design approach of the automatic gain control (AGC) loop in driving mode of MEMS gyroscopes. The designed control loop suggests that the system can maintain constant velocity output under variations of mechanical parameters. Moreover, the proposed method gives us more systematic approach and precise results. From the analysis it is shown that the proposed loop is absolutely stable for all kind of parameter variations. The simulations and experiments show that the automatic gain control loop is successfully applied to the control of drive oscillation mode of the MEMS gyroscope.

A novel demodulation method in MEMS gyroscope

This paper presents a novel approach for demodulation method of signal processing circuit in MEMS gyroscope. Since the MEMS gyroscope utilizes Coriolis acceleration that produces a modulated signal of the input angular velocity and driving signal, in order to measure the original angular rate, the demodulation process is essentially needed. The conventional AM demodulation process in MEMS gyroscope is sensitive to the phase difference between the output signal and the modulation reference signal. Moreover, the output is easily affected by nonlinear and noisy properties of a multiplying circuit. Proposed method eliminates the phase tuning of the demodulation stage and the multiplying process of the signal processing circuit that are likely to be major error factors of signal processing circuit but are essential parts of the conventional demodulation process in MEMS gyroscope. The proposed method utilized the envelope detection scheme of AM demodulation in communication system and modified it to apply to the electromechanical system of gyroscope. Experiments were accomplished to verify the performances. From the results, the proposed method shows a satisfactory performance without a multiplying component and tuning effort of the phase in signal process circuit.