Taesam Kang

Rate-based flow controllers for communication networks in the presence of uncertain time-varying multiple time-delays

An H^~ based robust controller is designed for a rate-feedback flow-control problem in single-bottleneck communication networks. The controller guarantees stability robustness to uncertain time-varying multiple time-delays in different channels. It also brings the queue length at the bottleneck node to the desired steady-state value asymptotically and satisfies a weighted fairness condition. Lower bounds for stability margins for uncertainty in the time-delays and for the rate of change of the time-delays are derived. A number of simulations are included to demonstrate the time-domain performance of the controller. Trade offs between robustness and time-domain performance are also discussed.

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 performance test of an oscillation loop for a MEMS resonant accelerometer

In this paper, the design, analysis and experimental results of the self-sustained oscillation loop for a tunable surface micromachined resonant accelerometer, ACRC-RXL are presented. The fabrication process of the mechanical structure is also illustrated. For the oscillation loop analysis, an operator-theoretical approach is applied based on the describing function technique. Using the analytical results, feedback parameters are designed and the expected loop performance is characterized. Then the accelerometer system is practically implemented using the mechanical structure and signal processing electronics. The experimental results show that the developed accelerometer has a performance of bias stability of about 0.7 mg and a dynamic range over 10 g, which satisfies the navigation-graded sensor performance.

Non-contact printing of high aspect ratio Ag electrodes for polycrystalline silicone solar cell with electrohydrodynamic jet printing

This paper presents a non-contact printing mechanism for high aspect ratio silver (Ag) electrodes fabricated by an electrohydrodynamic (EHD) jet printing technique. Using high viscosity Ag paste ink, we were able to fabricate narrow and high aspect ratio electrodes. We investigated the effect of the surface energy of the substrate and improved the aspect ratio of printed lines through multiple printing. We fabricated the polycrystalline silicone solar cell with the Ag electrode and achieved cell efficiency of around 13.7%. The EHD jet printing mechanism may be an alternative method for non-contact fabrication of solar cells electrodes.

Development of a tunable resonant accelerometer with self-sustained oscillation loop

In this paper, presented are a resonance type accelerometer, its implementation and results of performance test. The structure and principle of resonance type accelerometer are illustrated concisely. A pure surface micromachining technology is used for the structure manufacturing. Fundamental idea of this sensor is to detect variation of effective stiffness from parallel-plated electrostatic resonator. Since resonant accelerometer needs to keep track of the systems resonance point, a feedback loop called self-sustained oscillation loop is designed. The resonant point and its stability robustness are analyzed using nonlinear control methodologies, i.e., describing function method and extended Nyquist stability criterion. Environmental test and theoretical analysis confirmed that the oscillation loop is very robust to external disturbances.

H-Infinity Attitude Control System Design for a Small-Scale Autonomous Helicopter with Nonlinear Dynamics and Uncertainties

The paper focuses on the design of a robust H-infinity attitude controller for an unmanned small-scale helicopter. To take into account the salient nonlinearities, a model with six-degrees-of-freedom nonlinear dynamics and some linear approximation of the aerodynamic parts are used when extracting a linear model and performing simulations to check the performance of the designed controller. To design a robust H-infinity controller, an augmented plant is constructed by adjusting several weighting functions. Then, a robust controller is synthesized utilizing the augmented system with the weighting functions and H-infinity control methodology. Using computer simulation it is shown that the H-infinity controller works well when applied to the nonlinear model even though it is designed using a linear model approximation. Through frequency response analysis, it is shown that the proposed controller can overcome more than half of the uncertainty variations around a nominal point at the input side. The time-domain simulation with the nonlinear model demonstrates that the proposed controller is very robust in relation to the uncertainties, as was expected, overcoming large gain uncertainties and time delay in each input channel. The analysis and simulation results also show that the control system satisfies the Level 1 handling requirements, as defined in Aeronautical Design Standard ADS-33E-PRF.

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.

Improving mobile robot navigation performance using vision based SLAM and distributed filters

In this paper, we suggest a vision-based SLAM (simultaneous localization and mapping) method to improve navigation performance of mobile robot, which is used 2 encoders to calculate its position. If mobile robot is in building, tunnel or under ground facility, it is difficult to obtain navigation information from GPS only navigation system, because there are not enough visible GPS satellites. To overcome this limitation, DR (dead reckoning) system is required. However, as DR operation time goes by, the navigation error is increased because of accumulation of sensor error and noise. There are variety kinds of methods to reduce these errors. In this paper, we use a vision sensor and particle filter. Some clear points on vision sensor image are selected and tracked for error compensation. That is called a SLAM (simultaneous localization and mapping) method. In this paper, distributed particle filter is used to cope with nonlinear observation model and to deal with changing the number of measurements. Computer simulations are conducted to demonstrate the performance of suggested filter.

Vision-Based Indoor Localization for Unmanned Aerial Vehicles

Small unmanned aerial vehicles are cost-effective and easy to operate, and especially suitable in dangerous indoor environments. However, because GPS is not available in an indoor environment, indoor localization is a crucial problem in developing small unmanned aerial vehicles (UAVs). This paper suggests vision-based indoor localization for UAVs in GPS-denied environments. Our approach is based on image matching by applying the scale invariant feature transform algorithm.