This paper gives an evaluation of a low-cost MEMS accelerometer The accelerometer is intended for the distance measurement of a mobile robot or platform in short duration The distance traveled is obtained by double integration of the sensor signal with time Bias offset drift exhibited in the acceleration signal is accumulative and the accuracy of the distance measurement can deteriorate with time due to the integration This problem can be fixed by periodic recalibration with the help of external measurements on position, velocity and attitude These external signals can be calculated by an inertial system A Kalman filter can use the differences between these values to provide an optimum estimate of the system error The random bias drift of the accelerometer was found by experiment to be 25 mg The bias drift rate due to temperature was 0108 μg/s when the accelerometer was placed at room temperature With proper compensation on gravitation, the accelerometer can be a viable solution as a short duration distance-measuring device for a mobile robot

Evaluation of a Low-cost MEMS Accelerometer for Distance Measurement

An evaluation of a low-cost small-sized solid-state accelerometer is described in this paper. The sensor is intended for positioning of a mobile robot or platform. The acceleration signal output by the sensor is doubly integrated with time, which yields the travelled distance. Bias offset drift exhibited in the acceleration signal is accumulative and the accuracy of the distance measurement deteriorates with time due to the integration. This problem can be fixed by periodic recalibration by the use of external measurements on position, velocity, and attitude which can be compared with the corresponding quantities calculated by the inertial system. A Kalman filter could use the differences between those values to provide an optimum estimate of the system error. The random bias drift of the accelerometer was found experimentally to be 2.5 mg. The accelerometer was moved back and forth three times for a distance of 40 cm with an acceleration of 8 m/s/sup 2/. The final distance error accumulated was -1.08 cm. The bias drift rate due to temperature was 0.108 /spl mu/g/s when the accelerometer was placed at room temperature. The results show that the accelerometer could be a viable solution as a short-duration distance-measuring device for a mobile robot or platform.

/pdf/accelerometer-for-mobile-robot-positioning-wxgxuedscf.pdf

Accelerometer for mobile robot positioning

Antilock braking systems (ABS) are closed-loop devices designed to prevent locking and skidding during braking. Traction control systems (TCS) limit the amount of traction force generated at the wheels to prevent loss of traction. Both systems contain an electronic control unit (ECU), which compares signals from each wheel sensor. In ABS systems, the pressure to one or more of the wheels is regulated, whereas in TCS systems, the drive torque to the wheels is reduced.Recent advances include the use of wireless accelerometers, developments in the control software that take into account the dynamics of the tyres and suspension, the estimation of parameters such as lateral acceleration and wheel slip and the use of adaptive control and fuzzy logic. More recently, these systems have been integrated into other vehicle systems, such as four-wheel steering and active suspension. Future improvements might include the use of smart materials for sensor development, and the use of roadside-to-vehicle control.

Recent advances in antilock braking systems and traction control systems

In this paper a new combined method was applied to model the random drift of a micro-electro-mechanical system (MEMS) gyro to enhance its performance. The gyro is used to set up a micro-inertial -measurement unit (MIMU) for its low cost, low power consumption and small dimensions. To improve the MIMU's performance, we model the gyro's random drift by a statistic method. Given the paucity of the knowledge of fabrication of the gyro, we select a neural network model instead of making a delicate physical-mathematical model. Since the gyro we used is a tuning fork micro-machined sensor with large random drift, the modeling performance is affected by the randomness inherent in the output data when neural network approach is applied. Therefore, radial basis network structure, which was successfully applied to model temperature drift of fiber optical gyros, was chosen to build the model and the grey neural network. Compared with autoregressive model, the standard error of the gyro's random drift is reduced dramatically by radial basis model and grey radial basis model.

Modeling the Random Drift of Micro-Machined Gyroscope with Neural Network

An active thermal compensation system for a low temperature-bias-drift (TBD) MEMS-based gyroscope is proposed in this study. First, a micro-gyroscope is fabricated by a high-aspect-ratio silicon-on-glass (SOG) process and vacuum packaged by glass frit bonding. Moreover, a drive/readout ASIC, implemented by the 0.25 µm 1P5M standard CMOS process, is designed and integrated with the gyroscope by directly wire bonding. Then, since the temperature effect is one of the critical issues in the high performance gyroscope applications, the temperature-dependent characteristics of the micro-gyroscope are discussed. Furthermore, to compensate the TBD of the micro-gyroscope, a thermal compensation system is proposed and integrated in the aforementioned ASIC to actively tune the parameters in the digital trimming mechanism, which is designed in the readout ASIC. Finally, some experimental results demonstrate that the TBD of the micro-gyroscope can be compensated effectively by the proposed compensation system.

An integrated thermal compensation system for MEMS inertial sensors.

Micromachined silicon sensors offer tremendous cost, size, and reliability improvements for guidance, navigation, and control (GNC however, it will ultimately be driven by high-volume commercial markets with target prices below $25 per instrument. The paper describes advances in micromechanical gyro and accelerometer design and packaging. Performance of a prototype automotive traction control module, in pilot production, and a planned automobile suspension control module are described. The concept of a 3-cubic-inch, multi-purpose MEMS inertial system, based on a three-gyro, three-accelerometer system under development for a guided artillery shell, is discussed for automotive applications. Plans for future cost and size reduction are presented.

N. Barbour

Papers

Micromachined inertial sensors for vehicles