A Silicon Micromachined Gyroscope and Accelerometer for Vehicle Stability Control System

<div class="htmlview paragraph">The automotive industry has sought accurate, durable, and low cost mass produced angular rate sensors for chassis system control and navigational systems. An angular rate sensor based on the Coriolis force imposed on vibrating tuning forks has been developed for automotive applications.</div> <div class="htmlview paragraph">This newly developed angular rate sensor uses tuning forks made with fabricated elinvar metallic material. Size reductions in these sensors have reduced their weight and allowed for mounting directly on the printed circuit board of the electronic control module.</div> <div class="htmlview paragraph">Zero point temperature drift improvements have been developed through precision metal fabrication techniques.</div> <div class="htmlview paragraph">Reduced weight improved the sensor's impact resistence.</div>

<div class="htmlview paragraph">In today's automotive market, rollover protection systems are drawing an increasing attention. Unlike in conventional frontal and side impact events where linear accelerometers are used to detect the crash severity and make decision on deployment/non-deployment of the air bag restraint systems, rollover events require a new detection method using angular rate sensors. In the past, various angular rate sensors have been used in navigation systems to calculate pitch angle, or in camcorders for image stabilization. These sensors work at a low dynamic operating range, i.e. less than 100 degrees/sec. Angular rate sensors in automotive applications demand a higher dynamic capacity greater than 250 degrees/sec. (or °/s).</div> <div class="htmlview paragraph">This paper reviews automotive grade angular rate sensors currently being introduced for rollover protection system applications. In addition, various detection devices ranging from basic bubble sensing to newly developed sensors using micro-machined technology are also reviewed. The principle of Coriolis force used in the angular rate sensors is described. Pros and cons of each sensor type are discussed. Test methods to evaluate angular rate sensor performance and some typical sample data are also presented.</div>

<div class="htmlview paragraph">The reproduction of the vehicle motion is a crucial element of accident reconstruction. Apart from the position of the center of gravity in an inertial coordinate system, the vehicle heading plays an important role. The heading is the sum of the yaw angle and the vehicle body side slip angle.</div> <div class="htmlview paragraph">In standard vehicles, the yaw angle can be determined using the yaw rate sensor and the wheel speeds. However, the yaw rate sensor is often subject to temperature drift. The wheel speed signals are forged at low speeds or due to slip. These errors result in significant deviations of reconstructed and real vehicle heading. Therefore, an intelligent combination of these signals is required.</div> <div class="htmlview paragraph">This paper describes a fuzzy system which is capable to increase the accuracy of yaw angle calculation by means of fuzzy logic. Before the data is applied to the fuzzy system, it is preprocessed to ensure the accuracy of the fuzzy system inputs. Afterwards, the reliability of the described sensors is determined according to the driving situation. The heuristic knowledge about the reliability is implemented in the fuzzy system's knowledge base. The right choice of signal inputs is also important to conclude sensor reliability. Depending on the determined reliability, the significance of each individual sensor for yaw rate calculation is adapted. Measurements with a test vehicle proof the validity of the presented system. Tests with artificial errors analyze the fuzzy system's sensitivity to sensor failures.</div>

<div class="htmlview paragraph">This paper is directed to an <u>E</u>nhanced <u>T</u>raction <u>S</u>tability <u>C</u>ontrol System (ETSC) that is based on the estimate of vehicle yaw rate and does not require yaw rate or lateral accelerometer sensors information. The validity of the yaw rate estimate is determined and used to select the appropriate control methodology. We estimate the vehicle yaw rate based on the measured speeds of the un-driven wheels of the vehicle, and we utilize various other conditions to determine if the estimated yaw rate is valid for control purposes. When it is determined that the yaw rate is valid, a combined closed-loop yaw rate feedback, and an open-loop feed-forward derivative control based on the driver input is employed. Whereas in conditions under which it is determined that the estimated yaw rate is not valid, an open-loop feed-forward control with a proportional, derivative and a diminishing integrator terms, is employed. In addition, we develop a bank angle compensation algorithm using the steering angle, vehicle speed, and the estimated yaw rate to compensate for the effect of banked road. Test results indicate marked enhancement of vehicle stability with ETSC when compared with ABS and TCS. Finally, we present test results to compare the performance of ETSC system to yaw rate feedback control only <u>E</u>lectronic <u>S</u>tability <u>C</u>ontrol System (ESC) using yaw rate and lateral accelerometer sensors information.</div>

<div class="section abstract"><div class="htmlview paragraph">This paper presents an Interacting Multiple Model (IMM) based side slip angle estimation method to estimate side slip angle under various road conditions for vehicle stability control. Knowledge of the side slip angle is essential enhancing vehicle handling and stability. For the estimation of the side slip angles in previous researches, prior knowledge of tire parameters and road conditions have been employed, and sometimes additional sensors have been needed. These prior knowledge and additional sensors, however, necessitates many efforts and make an application of the estimation algorithm difficult. In this paper, side slip angle has been estimated using on-board vehicle sensors such as yaw rate and lateral acceleration sensors. The proposed estimation algorithm integrates the estimates from multiple Kalman filters based on the multiple models with different parameter set. The IMM approach enables a side slip angle estimation from originally equipped vehicle sensors without prior knowledge of tire and road. The proposed estimation algorithm is evaluated via vehicle tests in electronic control unit level. The results have shown that the proposed estimator can successfully estimate side slip angles without any information on tire-road friction.</div></div>

Silicon micromachined gyroscope (SMG) is a new sensor technique used for rolling object moving control. One of the difficulty is how to get position parameters from gyroscope signal that is a multiplicave blind signal. This paper analysis the signal property and provide several methods to get the position parameters. The results show the new method do well. Otherwise as the signal from SMG contains struggle noise, we adopt some methods to cancel the noise. Results also show the methods very efficient.

<div class="htmlview paragraph">The best features of a comb and ring device have been combined to provide an improved micromachined angular rate sensor. The use of differential combs attached to a centrally supported ring gives this electroformed surface micromachine improved signal output and temperature performance. Previous results have been reported for vibratory ring sensors vacuum packaged in solder sealed CERDIPs. Bulk silicon etching and wafer to wafer bonding, used to fabricate millions of pressure sensors and accelerometers each year, have been employed to vacuum package this new CMOS integrated micromachine. Wafer level packaging allows for MEMS chip-scale packaging at the board level. The goal of this project is to develop a low cost sensor capable of reliably functioning at temperatures between -40 °C and 85 °C. The design, modeling, process, package, performance and automotive applications of this sensor will be covered.</div>

<div class="section abstract"><div class="htmlview paragraph">This paper provides several examples of silicon “micromachined” semiconductor sensors with which the authors are involved for aerospace condition monitoring. This and related work in MEMS (Micro Electro Mechanical Systems) has the potential to revolutionize condition monitoring in aerospace condition and “health monitoring” by (1) moving “smart” electronics out to the sensor chip itself and (2) combining a vast quantity and types of, not only electronic, but micromechanical sensing schemes into the silicon chip . Precisely formed cantilevers, gears, valves, microplumbing and even micro motors of the cross-section of a human hair can be fabricated on a single silicon microchip.</div><div class="htmlview paragraph">Silicon is an excellent mechanical material with a yield strength several times that of stainless steel. Also silicon has excellent thermal properties , whereas compatible silicon dioxide (which we typically use in connection with silicon microelectronics patterning) is virtually a thermal insulator. Other compatible thin films such as silicon nitride or even diamond (which we can now grow) provide an increased variety of microelectromechanical tools which can be formed to specifications of submicron dimension (a human hair is about 100 microns in diameter).</div><div class="htmlview paragraph">Silicon has not been thought of as a high temperature material because conventional microelectronics is limited pretty much to the military range because of leakage in p-n junctions. This has limited silicon electronic applications in some of the more harsh aerospace applications, however silicon as a material will function well above 1000C for many mechanical applications in hot aerospace arenas. <b>At cryogenic temperatures</b> (except for the liquid hydrogen to liquid helium range) many silicon microelectronic circuits can be made to function even better than at room temperatures.</div><div class="htmlview paragraph">In this paper, we survey several micromachined sensors which we have under development for aerospace applications, such as a micro flowsensor for gases and liquids, a fatigue and crack detection and imaging microchip, a hydrogen and gas leak detection microsensor as an inverse microspectrometer, a “smart” vibration microsensor, silicon microactuators, and silicon micromachined pressure sensors for harsh environments.</div></div>

Deep reactive-ion etching (DRIE) is commonly used for high aspect ratio silicon micromachining. However, scalloping, which is the result of the alternating Bosch process of DRIE, can cause many problems in the subsequent process and degrade device performance. In this work, we propose a simple and effective method to smoothen the scalloping of DRIE trenches. The proposed method utilizes sidewall dry etching by reactive-ion etching (RIE) based sulfur hexafluoride (SF6) plasmas, following the DRIE process. To investigate the effect of the etch parameter on the scallop smoothing effect, the radio frequency (RF) power and gas flow are controlled. After the RIE treatment, the scallop smoothing effects were evaluated by measuring the average scallop depth under each condition. The scallop depth was reduced by 91% after implementing the scallop smoothing technique using RIE. Thus, our smoothening method based on SF6 plasmas would provide broad availabilities and applicability in silicon micromachining with the simple low-temperature process.

A simple, low‐cost and reliable dicing‐free silicon‐on‐insulator (SOI) process is presented for solving three major challenges in manufacturing the microelectromechanical systems devices, i.e. stiction, notching and dicing damage. In this process, the cavity is used and patterned on the handle layer to solve the stiction problem, and the exposed oxide is removed in hydrofluoric acid (HF) solution before deep reactive ion etching (DRIE) on the structure layer to eliminate the notching effect's impact. The dies are attached temporally to a designed frame by the silicon dioxide. After removing the oxide using HF solution, the dies are separated from the wafer cleanly without dicing damage. The layout design rules on the front side and backside patterns are established. Furthermore, a grooved carrier wafer with specific design rules was introduced to enhance the yield rate of the process. Finally, a tuning fork gyroscope was fabricated to demonstrate the proposed fabrication process and a yield rate of over 81% was achieved. The process solves the stiction, notching and dicing damage problems only involving the apparatus associated with lithography and DRIE, offering an economic and complete SOI process solution.

The notching and stiction problem, which widely exists in silicon on insulator (SOI) microstructure fabrication, were resolved in this study. In this paper, a new plasma trench technique that is based on the deep reactive ion etching (DRIE) process is proposed. In this modified process, the deep reactive ion etching (RIE) was divided into several steps, where conformal plasma enhanced chemical vapor deposition (PECVD) oxide coating, and directional oxide etch back were employed to prevent the notching effect and the reactive ion etching (RIE) lag effect is also improved. Therefore, the microstructures regardless of the feature sizes could be realized. The stiction problem is eliminated by using dry chemical release replacing wet release in this approach, where the notching effect is used. The notching or footing effect was exploited for attaining the lateral etch following the deployment of the anisotropic plasma etching of the inductively coupled plasma (ICP). This method was proven useful for both the uniform and non-uniform feature designs. With this novel process, the high aspect ratio beams can be obtained. The thickness of the silicon layer is 75 μm, while the depth of the beams is 70 μum where the 5 μm silicon was etched to suspend the movable beams. The aspect ratio is as high as 35. Trenches with very different widths of 2.5 μm and 35 μm are also achieved at the same time.

This paper shows how to use silicon pressure sensors for high temperature and silicon corrosive environments. A sensor chip has been developed to be used in high temperature up to 300/spl deg/C, which has SOI (Silicon On Insulator) structure employing Si/Al/sub 2/O/sub 3//Si double hetero-epitaxial technology[1]. The sensor chip is covered with a stainless diaphragm, and never contact with media of pressure. In experiments, a pressure sensor which is designed for a range of 1 MPa has a sensitivity of 18.3 mV/V/MPa. After compensating of the temperature influence, a maximum offset error of 1.3%F.S., and a maximum sensitivity error of 1.1%F.S. from 50/spl deg/C to 200/spl deg/C were obtained.

<div class="section abstract"><div class="htmlview paragraph">This paper presents a study on the state estimation of out-of-plane dynamics of motorcycles based on the Sharp 71 model. The Sharp 71 model is a linear time-variant system that describes the out-of-plane dynamics of a motorcycle. Comparisons with multi-body simulations and measurement data show that this relatively simple model is capable of principally representing the lateral dynamics of the motorcycle. Two relevant variables of out-of-plane dynamics are the roll angle and the tire lateral forces. The structure of the Sharp 71 model offers the possibility of estimating these two variables model-based with the aid of corresponding measured output variables. The input variable is the steering torque, which obviously cannot be measured with reasonable effort. Therefore, an unknown-input observer is used to estimate the states. This state estimator allows a systematic consideration of the unknown input variable. The unknown-input observer is designed for different sets of outputs and the corresponding effects on the results are considered. The sensors used include gyroscope, acceleration sensor and steering angle sensor. The longitudinal velocity as time-variant parameter considers the coupling of the out-of-plane model with longitudinal dynamics. The implementation is achieved with gainscheduling of the observer feedback. The implemented concept is evaluated regarding its performance and convergence. Simulation studies are used as well as an evaluation based on measurement data. The simulation test was carried out with the help of a multi-body simulation. A comparison with a purely IMU-based roll angle estimator is presented for the handling course test. The results are of great interest, since in modern driver assistance systems, knowledge of the current dynamic vehicle condition is essential. With the aid of turn rate and acceleration sensors, important parameters such as roll angle are already recorded. The use of comprehensive physical motorcycle models is a pursued approach to further detail the vehicle state estimates. In combination with modern control engineering methods, other important driving dynamics variables can be calculated, such as the lateral forces of the tyres in this case. The results based on the simple Sharp 71 model already yields stable estimates of the essential state variables. The results also give information about the necessary level of detail of the used physical model and allow a principal assessment of the observer convergence during high dynamic maneuvers.</div></div>

The structure and principle of silicon micro-machined gyroscope used for rotating carrier is introduced. The dynamic equations of axially moving are derived by analyzing three-axis moving of MEMS three-axis simulator. The result of simulation shows three moving locus of the head of rolling airframe missile, and three output signals from silicon micro-machined gyroscope which fix on inner plate of three-axis simulator, some rules of three output signals of three moving locus are gained. The signal of the gyroscope couples the frequency of the rotating carrier which makes the coning motion, so the frequency of the coning motion is contained when detecting the frequency of the rotating carrier using the signal of the gyroscope. By analyzing the output signals using Fast Fourier Transform (FFT) algorithm, subtracting the frequency of the rotating carrier, and the relative error is only 1.25% by detecting the self-rotating frequency of the rotating carrier.

A new silicon resonant angular rate sensor is presented. The sensor consists of a packaged glass-silicon-glass structure and is made by a batch-fabrication process. The sensor is a tuning fork with both sides suspended by torsion bars. Electromagnetic excitation and capacitive detection are used. The applied angular rate generates the Coriolis' force and the resonator starts torsional vibration around the torsion bars. The test device shows a sensitivity of 0.7 fF sec/deg. In this paper, the working principles, fabrication process, and simulated and measured outputs of the sensor are described. The scaling rule of the angular rate sensor are also considered.