Tsung-Lin Chen

Vehicle Full-State Estimation and Prediction System Using State Observers

This paper presents a novel vehicle full-state estimation and prediction system that employs a ldquofull-state vehicle modelrdquo together with lateral acceleration, longitudinal velocity, and suspension displacement sensors to obtain the current and future vehicle state information. The full-state vehicle model is a vehicle model with 6 degrees of freedom (DOFs) and is described by 20-state nonlinear differential equations. The proposed approach differs from those in most of the existing literatures in three aspects. First, the road angles and the nonlinear suspension systems are incorporated into the vehicle modeling. Second, the ldquoswitching observer schemerdquo is introduced to significantly reduce the heavy work load that is required for the mathematical derivations. Finally, the full-state vehicle model is employed to predict the vehicle dynamics at future times. The simulation results show that the proposed system can accurately estimate and predict the state values. The relative accuracy of the state estimation is 2.66% on average and 2.86% on average of the state prediction. Furthermore, the proposed system can predict whether the vehicle rollover will occur when a vehicle performs a quick turn on a slope road.

Design and fabrication of MEMS logic gates

This paper presents a novel design of MEMS logic gate that can perform Boolean algebra the same as logic devices that are composed of solid-state transistors. This MEMS logic gate design inherits all the advantages from MEMS switches and thus is expected to have more applications than MEMS switches. One unique feature of this device is that it can perform either NAND gate or NOR gate functions with the same mechanical structure but with different electrical interconnects. In a prototype design, the device is 250 µm long, 100 µm wide and has 1 µm gap. The experimental results show that this device can operate at 10/0 V and achieve the proposed logic functions. The resonant frequency of the device is measured roughly at 30 kHz. Due to no metal-to-metal contact in the current device, the logic functions of the design are verified through observations and video taping.

MEMS SoC: observer-based coplanar gyro-free inertial measurement unit

This paper presents a novel design of a coplanar gyro-free inertial measurement unit (IMU) that consists of seven to nine single-axis linear accelerometers, and it can be utilized to perform the six DOF measurements for an object in motion. Unlike other gyro-fee IMUs, this design uses redundant accelerometers and state estimation techniques to facilitate the in situ and mass fabrication for the employed accelerometers. The alignment error from positioning accelerometers onto a measurement unit and the fabrication cost of an IMU can greatly be reduced. The outputs of the proposed design are three linear accelerations and three angular velocities. As compared to other gyro-free IMUs, the proposed design uses less integral operation and thus improves its sensing resolution and drifting problem. The sensing resolution of a gyro-free IMU depends on the sensing resolution of the employed accelerometers as well as the size of the measurement unit. Simulation results indicate that the sensing resolution of the proposed design is 2° s−1 for the angular velocity and 10 μg for the linear acceleration when nine single-axis accelerometers, each with 10 μg sensing resolution, are deployed on a 4 inch diameter disc. Also, thanks to the iterative EKF algorithm, the angle estimation error is within 10−3 deg at 2 s.

An Optimal Wheel Torque Distribution Controller for Automated Vehicle Trajectory Following

This paper proposes an automated vehicle trajectory following system that uses four constrained wheel torques to regulate a vehicle on a reference trajectory. The constrained wheel torques can be achieved using the two-wheel drive and differential brakes. The proposed control algorithm is developed using the following steps. First, the sliding-mode control is used to find stability constraints for trajectory following when the vehicle system is subjected to modeling errors. Second, these stability constraints, along with other actuator constraints, are particularly tuned for the proposed control distribution method. The proposed control distribution method determines four longitudinal tire forces and minimizes actuator control efforts. Finally, these tire forces are converted to traction/braking wheel torques. The proposed method has the following advantages: 1) It achieves both robust trajectory following and optimal control efforts, 2) the optimal control effort is obtained analytically instead of from a numerical search, and 3) the robust performance of this vehicle control system can be theoretically verified. The proposed method is evaluated using numerical simulations on two front-drive vehicle models: a full-state vehicle model and a sedan model from the Carsim commercial software. The simulation results indicate that, in both cases, the proposed method can regulate the vehicle to finish a “double-lane change” when the vehicle is moving at an initial speed of 90 km/h. The maximum lateral acceleration is 6.56 m/s2, and the regulated position error is less than 6.9 cm.

Vehicle Dynamic Prediction Systems with On-Line Identification of Vehicle Parameters and Road Conditions

This paper presents a vehicle dynamics prediction system, which consists of a sensor fusion system and a vehicle parameter identification system. This sensor fusion system can obtain the six degree-of-freedom vehicle dynamics and two road angles without using a vehicle model. The vehicle parameter identification system uses the vehicle dynamics from the sensor fusion system to identify ten vehicle parameters in real time, including vehicle mass, moment of inertial, and road friction coefficients. With above two systems, the future vehicle dynamics is predicted by using a vehicle dynamics model, obtained from the parameter identification system, to propagate with time the current vehicle state values, obtained from the sensor fusion system. Comparing with most existing literatures in this field, the proposed approach improves the prediction accuracy both by incorporating more vehicle dynamics to the prediction system and by on-line identification to minimize the vehicle modeling errors. Simulation results show that the proposed method successfully predicts the vehicle dynamics in a left-hand turn event and a rollover event. The prediction inaccuracy is 0.51% in a left-hand turn event and 27.3% in a rollover event.

Design, fabrication and calibration of a novel MEMS logic gate

This paper presents the design, fabrication and calibration of a novel MEMS logic gate that can perform Boolean algebra as well as logic devices composed of solid-state transistors. Unlike existing designs, the proposed design can perform either NAND gate or NOR gate functions using the same mechanical structure, but different electrical interconnects. The proposed design imposes three requirements on the fabrication process: two voltage levels carried on a suspended plate, metal-to-metal contact between shuttle electrodes and fixed electrodes, and a low process temperature (<300 °C). To fulfill these requirements, the residual stress in the fabricated device is substantial which could impair the functionality of the device. Therefore, a novel in situ film stress calibration method is developed to assist the development of the fabrication process. In a prototype design, the fabricated device is 250 μm long, 100 μm wide and of 3.97 μm gap. Experimental results show that the device can operate at 25/−25 V and 100 Hz, and achieve the proposed logic functions. In addition, several properties of this device are experimentally evaluated, including power consumption, on/off resistance, lifetime and resonant frequency.

A gyroscope control system for unknown proof mass and interface circuit errors

This paper presents a novel approach that can compensate errors resulting from the imperfections of mechanical structures and interface circuits for MEMS gyroscope systems. The mechanical structure errors discussed in this paper contribute to unknown proof mass, spring constants, damping coefficients, and existence of cross-axis resilient/damping forces. The interface circuit errors include: mismatch of differential capacitors, parasitic capacitance, offset voltage of operation amplifiers, and circuit noise. Different from most of existing researches, the proposed method has the following features: (1) the mechanical structure imperfections and interface circuit errors are compensated simultaneously using control techniques; (2) the mass of the proof mass can be unknown. This approach is verified on two types of gyroscope designs by numerical simulations. Simulation results indicate that, under those imperfections, the proposed method can obtain correct angular rate within 80 milliseconds.

MEMS gyroscope control systems for direct angle measurements

This paper presents a control algorithm for vibrating gyroscopes so that they can directly measure the rotation angle without integrating the angular rate. In most gyroscope systems, the rotation angles were obtained by integrating the angular rate, thus suffer from the error accumulation problem. Only a few papers reported that they could compensate the imperfect dynamics in gyroscopes and obtain the rotation angle directly. However, they either required a calibration phase prior to the normal operation or their stability was not theoretically proven. This paper proposes a one-step control algorithm so that imperfection compensation and angle measurement can be done simultaneously. In a demonstrating case, the mechanical structure uncertainties caused 10%∼20% parameter variations in a gyroscope system; the signal are contaminated by zero-mean white noise with the PSD of 2.3×10−15(ms−1)2/Hz; the angular rate to be measured is 4sin(2π × 40t) rad/sec. The proposed algorithm can obtain the rotation angle with an accuracy less than 0.5 degree.

Applying a three-antenna GPS and suspension displacement sensors to a road vehicle

This paper presents a novel sensor fusion system for road vehicles, which mainly composed of a three-antenna global positioning system (GPS), and four suspension displacement sensors. This sensor system not only obtains accurate six degree-of-freedom (DOF) information for vehicle dynamics but also road angles in real time. The road angles and vehicle attitude are difficult to be detected using on-board sensors because they are often coupled in the sensor measurements. Most approaches ignore this coupling effect; only a few try to obtain them by state estimations using vehicle models. The proposed method solve this problem, without requiring any vehicle model, by incorporating a non-inertial sensor (suspension displacement sensors) with inertial sensors (three-antenna GPS). In a demonstrating case, an additional inertial measurement unit (IMU) is included in the senor system to improve the estimation accuracy. Simulation results indicate that the accuracy of the estimated vehicle attitude is less than 0.85 deg, and that of the estimated road angles is less than 0.3 deg. Additionally, the estimation accuracy of the vertical displacement is improved from 3 m to 0.248 m.

A constrained wheel torque controller for lane following system using control distribution

A lane following system is proposed that employs four constrained wheel torques to regulate a vehicle on a reference trajectory. The proposed control algorithm was developed by combining several techniques such as: DYC method, hierarchical control architecture, sliding mode controls, control distributions, and etc. Different from existing approaches, the proposed method has the following advantages: (1) it can be implemented on two-wheel drive vehicles; (2) the error resulting from the hierarchical architecture are minimized and compensated; (3) the controlled wheel torque calculated by the control distribution method is an analytical solution instead of from numerical search. The proposed controller is evaluated by simulations on two more complex vehicle models: a full-state vehicle model and a sedan model from commercial software Carsim. Simulation results indicate that, in both cases, the proposed method can regulate the vehicle to finish a single lane change when the vehicle is moving at an initial speed of 90 km/hr.