Lateral Comb Resonator Research Articles

Fault Diagnosis of MEMS Lateral Comb Resonators Using Multiple-Model Adaptive Estimators

In this brief a fault diagnostic unit is developed for microelectromechanical systems (MEMS) by means of multiple model adaptive estimation technique. Fault modeling tools such as contamination and reliability analysis of microelectromechanical layout enabled interpretation of microsystems behavior by evaluating their structural variations and modeling them in form of electric circuits. This technique cannot directly diagnose the faults during operation of microsystems. However, these fault-representing models can be used in multiple model adaptive estimation technique to form fault diagnosis units. Here, fault-representing systems are modeled by Kalman filters in real-time applications and are used to evaluate the fault in microsystems. MEMS lateral comb resonators are fabricated to experimentally demonstrate the fault diagnosis performance in multiple model adaptive estimation technique.

Structure Rotation and Pull-in Voltage Control of MEMS Lateral Comb Resonators Under Fault Conditions

Lateral comb resonators (LCRs) theoretically possess a symmetric structure; therefore, the electrostatic force is effective only along the axis of displacement and is neutralized elsewhere. This force is not a function of the distance between the stationary and the moving (shuttle) plates in the direction of the movement. However, manufacturing imperfections and fault conditions make the device operate asymmetrically and cause rotation of the shuttle structure in a lateral gap-closing direction, putting the device in an unstable region of operation (pull-in voltage limit). In this region, the rotated structure experiences an extra force which pulls the device into the region of instability beyond the pull-in voltage limits. This paper illustrates the application of variable structure controllers to correct such behavior and to compensate for the uncertainties that exist in the microsystem parameters. The controller is equipped with a self-tuning parameter estimation block and is designed to control the LCRs under both normal and fault conditions. The controller utilizes through-wafer optical monitoring to provide the position feedback signal. The controller is implemented in a real-time control board and is experimentally verified to demonstrate the effectiveness of the control method under different operating conditions.

Fault Diagnosis of Time-Varying Parameter Systems With Application in MEMS LCRs

Multiple-model adaptive estimation (MMAE) is a well-known technique used for model matching of deterministic parameter systems. This technique can be used in fault diagnosis by allocating a model to each type of fault. In each contingency, the model that represents the behavior of the actual system can indicate the type of fault occurrence. Kalman filters are generally used in modeling and residual-signal generation of time-invariant systems. Slowly time-varying parameter systems, however, require a system identification unit in addition to the model-matching core. This paper utilizes the least square forgetting-factor technique in parameter identification of slowly time-varying systems and combines it with MMAE for fault-diagnosis applications in microelectromechanical-systems (MEMS) lateral comb resonators (LCRs). Prescheduled faults were designed for simulations and experimentally examined in real-time implementations of estimation-based diagnosis technique for two fabricated MEMS LCRs. It is shown that the application of a system identification unit significantly increases the performance of the fault diagnosis in MEMS devices.

Reliability Enhancement of MEMS Lateral Comb Resonators Under Fault Conditions

The delicate structure of microelectromechanical systems (MEMS) limits their reliability in cases of fault occurrence. Control systems can enhance their reliability of operation by providing fault robust systems. This paper illustrates a method for the safe operation of lateral comb resonators (LCR) under faulty conditions. Different types of fault are fabricated at chip level and experimentally tested in order to demonstrate the effectiveness of the reliability enhancement of operation in LCRs. Mass change and folded spring structural defects influence the device's behavior and reduce its reliability of operation. Here, model reference adaptive controllers (MRACs) are effectively used to enhance the reliability of faulty devices. Reliable operation of a +5% additional mass considering environmental conditions and asymmetries on the device, demand almost 80% higher control effort whereas +20% in case of broken trusses or +46% in case of adhesion point fault on a beam of folded springs. The simulation and experiment results demonstrate successful application of MRAC for reliable operation of LCRs by providing a fault-robust system.

Sliding mode-based microstructure torque and force estimations using MEMS optical monitoring

The determination of microstructure state is becoming of increasing importance for microelectromechanical system (MEMS) sensors and actuators. Sliding mode-based microtorque estimation for a rotary micromotor, assuming the availability of a MEMS optical monitoring data stream, is presented. The dynamic model of the rotating MEMS system and the electrostatic torque are identified. The technique uses the estimated position signal to approach the actual measured position signal, obtainable through optical monitoring, to simultaneously estimate the microtorque and load torque. The estimated microtorque and load torque are low-pass filtered to eliminate the switching behavior inherent in the sliding-mode estimator. The experimental setup of a lateral comb resonator with optical monitoring is presented and discussed. The simulation results of both electrostatic and load torque estimations are presented, as well as the experimental force estimation of a lateral comb resonator device.

Real-time translational control of a MEMS comb resonator

Closed-loop control has been successfully applied to a microelectromechanical systems (MEMS) lateral comb resonator device in real-time to perform impulse disturbance damping and sinusoidal position control, enabled by the use of a through-wafer optical microprobe to obtain position feedback. This result leverages the application of lifetime, in-situ control of MEMS in order to provide quality assurance of microsystems in safety critical applications. A position feedback signal produced by a through-wafer optical microprobe has been used for comb resonator system model identification by two independent methods to accurately determine the effective mass, damping, and spring constant values of the device. After accurate determination of system parameters, closed-loop impulse disturbance damping and proportional-integral-differential (PID) translational control were applied. Closed-loop control results presented indicate controllability of such microstructures and response times on the order of the natural frequency of the device.

Grating-enhanced through-wafer optical microprobe for microelectromechanical system high-resolution optical position feedback.

We present modeling and experimental results from the use of a 1310-nm-wavelength through-wafer optical microprobe in conjunction with a microstructure grating to monitor the motion of a lateral comb resonator stage. The optical signal that results from shuttle interaction with the microprobe beam exhibits a peak-to-valley dynamic range that corresponds to 2-microm microstructure displacement, facilitating submicrometer positional resolution on digitization. This signal was used to achieve microstructure positional feedback and effective microsystem model parameter extraction, which are essential for structure control and model-based fault detection.

Through-wafer optical probe characterization for microelectromechanical systems positional state monitoring and feedback control

Implementation of closed-loop microelectromechanical sys- tem (MEMS) control enables mechanical microsystems to adapt to the demands of the environment that they are actuating, opening a broad range of new opportunities for future MEMS applications. Integrated op- tical microsystems have the potential to enable continuous in situ optical interrogation of MEMS microstructure position fully decoupled from the means of mechanical actuation that is necessary for realization of feed- back control. We present the results of initial research evaluating through-wafer optical microprobes for surface micromachined MEMS in- tegrated optical position monitoring. Results from the through-wafer free- space optical probe of a lateral comb resonator fabricated using the multiuser MEMS process service (MUMPS) indicate significant positional information content with an achievable return probe signal dynamic range of up to 80% arising from film transmission contrast. Static and dynamic deflection analysis and experimental results indicate a through- wafer probe positional signal sensitivity of 40 mV/mm for the present setup or 10% signal change per micrometer. A simulation of the applica- tion of nonlinear sliding control is presented illustrating position control of the lateral comb resonator structure given the availability of positional state information. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)00312-3)