Jingyan Dong

Stress focusing for controlled fracture in microelectromechanical systems

This letter describes a strategy for controlling fracture in microelectromechanical systems (MEMSs) based on the control of corner sharpness. Studies of model MEMS structures with round (radius of approximately microns), intermediate, and sharp (<10nm) corners demonstrate the effects of corner sharpness on the concentration of applied stress. Finite-element analysis reveals that stress distributions intensify and localize as sharpness increases, and transfer printing experiments demonstrate the influence of stress concentration on breakability.

Robust Control of a Parallel- Kinematic Nanopositioner

This paper presents the design, model identification, and control of a parallel-kinematic XYZ nanopositioning stage for general nanomanipulation and nanomanufacturing applications. The stage has a low degree-of-freedom monolithic parallel-kinematic mechanism featuring single-axis flexure hinges. The stage is driven by piezoelectric actuators, and its displacement is detected by capacitance gauges. The control loop is closed at the end effector instead of at each joint, so as to avoid calibration difficulties and guarantee high positioning accuracy. This design has strongly coupled dynamics with each actuator input producing in multiaxis motions. The nanopositioner is modeled as a multiple input and multiple output (MIMO) system, where the control design forms an important constituent in view of the strongly coupled dynamics. The dynamics that model the MIMO plant is identified by frequency domain and time-domain identification methods. The control design based on modem robust control theory that gives a high bandwidth closed loop nanopositioning system, which is robust to physical model uncertainties arising from flexure-based mechanisms, is presented. The bandwidth, resolution, and repeatability are characterized experimentally, which demonstrate the effectiveness of the robust control approach.

Electrostatically Actuated Cantilever With SOI-MEMS Parallel Kinematic

This paper presents the design, analysis, fabrication, and characterization of an active cantilever device integrated with a high-bandwidth 2-DOF translational (XY) micropositioning stage. The cantilever is actuated electrostatically through a separate electrode that is fabricated underneath the cantilever. Torsion bars that connect the cantilever to the rest of the structure provide the required compliance for the cantilevers out-of-plane rotation. The active cantilever is carried by a micropositioning stage, which enables high-bandwidth scanning to allow manipulation in three dimensions. The design of the microelectromechanical system stage is based on a parallel kinematic mechanism (PKM). The PKM design decouples the motion in the X- and Y-directions while allowing for an increased motion range with linear kinematics in the operating region (or workspace). The trusslike structure of the PKM also results in increased stiffness and reduced mass of the stage. The integrated cantilever device is fabricated on a silicon-on-insulator (SOI) wafer using surface micromachining and deep reactive ion etching processes. The actuation electrode of the cantilever is fabricated on the handle layer, while the cantilever and the XY stage are at the device layer of the SOI wafer. Two sets of electrostatic linear comb drives are used to actuate the stage mechanism in the X- and Y-directions. The cantilever provides an out-of-plane motion of 7 mum at 4.5 V, while the XY stage provides a motion range of 24 mum in each direction at the driving voltage of 180 V. The resonant frequency of the XY stage under ambient conditions is 2090 Hz. A high quality factor (~210) is achieved from this parallel kinematic XY stage. The fabricated stages will be adapted as chip-scale manufacturing and metrology devices for nanomanufacturing and nanometrology applications.

XY

This paper presents a method for driving a MEMS electrostatic actuator, while simultaneously sensing the resulting displacement/capacitance without the use of an additional physical sensing structure. The approach superposes the sensing and actuation signals into a single input into the system and obtains its mechanical (displacement) response from the modulation (amplitude or phase) it produces on the sensing input. The approach is analyzed and experimentally shown to produce an amplitude modulation of 0.1857 mV µm−1 of displacement on electrostatic drive that produces a displacement of 14 µm at 100 V and a 0.55 pF capacitance change from a nominal capacitance of 0.35 Pico farads. The approach enables a very cost-effective and convenient approach to detect the displacement of MEMS devices for a variety of applications in the laboratory environment, and provide a potential feedback signal for closed-loop control of electrostatically driven MEMS devices.

Stage

This paper presents the design, kinematics, fabrication and characterization of a monolithic micro positioning two degree-of-freedom translational (XY) stage. The design of the proposed MEMS (micro-electro-mechanical system) stage is based on a parallel kinematics mechanism (PKM). The stage is fabricated on a silicon-on-insulator (SOI) substrate. The PKM design decouples the motion in the XY directions. The design restricts rotations in the XY plane while allowing for an increased motion range and produces linear kinematics in the operating region (or workspace) of the stage. The truss-like structure of the PKM also results in increased stiffness by reducing the mass of the stage. The stage is fabricated on a silicon-on-insulator (SOI) wafer using surface micromachining and a deep reactive ion etching (DRIE) process. Two sets of electrostatic linear comb drives are used to actuate the stage mechanism in the X and Y directions. The fabricated stage provides a motion range of more than 15 µm in each direction at a driving voltage of 45 V. The resonant frequency of the stage under ambient conditions is 960 Hz. A high Q factor (~100) is achieved from this parallel kinematics mechanism design.

Simultaneous actuation and displacement sensing for electrostatic drives

This paper presents the design and implementation of robust control schemes for two applications of a nanopositioning stage (1) reference trajectory tracking with high resolution over a given bandwidth (2) control design for repetitive motions. The stage has a low degree of freedom monolithic parallel kinematic mechanism using flexure hinges. It is driven by piezoelectric actuators and its displacement is detected by capacitance gauges. The design has strongly coupled dynamics with each actuator input producing in multi- axis motions. The nano-positioner is modeled as a multiple input and multiple output (MIMO) system, and the MIMO plant model is identified by time-domain identification methods. The design of the nano-positioner relies heavily on the control design to account for the high coupling in the system. The proposed Hinfin MIMO controller achieves a good performance in terms of resolution, bandwidth and robustness to the modeling uncertainty. In the second part of the paper, we present control design for tasks that require repetitive motion of nano positioning system. These tasks are quite common in micro/nano manipulation and manufacturing. This paper presents a robust control design that gives a significant (over thirty fold) improvement in tracking of repetitive motions on a prespecified frequency band. This design, unlike other schemes, is robust to modeling uncertainties that arise in flexure based mechanisms, and does not require any learning steps during its real time implementation. This design scheme is implemented on a parallel-kinematics XYZ nano positioning stage for repetitive nano-manipulation and nano-manufacturing applications.

Design, fabrication and testing of a silicon-on-insulator (SOI) MEMS parallel kinematics XY stage

This paper presents the design, analysis, fabrication, and characterization of a closed-loop XY micropositioning stage. The stage design is based on a 2 degree-of-freedom parallel kinematic mechanism with linear characteristics. Integrated with sensing combs, and fabricated in SOI wafers, the design provides a promising pathway to closed-loop positioning microelectromechanical systems platform with applications in nanomanufacturing and metrology. The XY stage provides a motion range of 20 micrometers in each direction at the driving voltage of 100 V. The resonant frequency of the XY stage under ambient conditions is 600 Hz. The positioning loop is closed using a capacitance-to-voltage conversion IC and a feedback controller is used to control position with an uncertainty characterized by a standard distribution of 5.24 nm and a closed-loop bandwidth of about 30 Hz.

Robust MIMO control of a parallel kinematics nano-positioner for high resolution high bandwidth tracking and repetitive tasks

This paper presents a coordinated design framework for precision motion control (PMC) systems. In particular, the focus is on the design of feedback and feedforward controllers operating on systems that repeatedly perform the same tasks. The repetitive nature of the tasks suggests the use of Iterative Learning Control (ILC). However, in addition to the repeatability of the desired trajectory, the class of systems under study examines the effect of non-repeating disturbances and possible reset errors. The rejection of uncertain, but bounded, disturbances suggests the use of H infin design. The non-repeating disturbances and reset errors necessitate coordination of the feedback and feedforward designs. The assumption that the disturbances have a particular frequency distribution affords a frequency domain separation between the two controller degrees of freedom. Experimental results are given on a piezo-driven nanopositioning device demonstrating the benefits to the presented approach.

A 2 Degree-of-Freedom SOI-MEMS Translation Stage With Closed-Loop Positioning

The rapid growth in nanosciences and technology has increased the need for high-precision nanopositioning stage technology, an important aspect of which is calibration to a traceable length standard with nanometre resolution. Direct calibration of the entire displacement range to a traceable length standard is generally difficult and time consuming because of the dearth of suitable and stable references and the need to remove all environmental disturbances during the calibration procedure. This paper introduces an approach to implementing self-calibration on a single-axis, dual-actuated, nanopositioning stage. It demonstrates how dual actuation on such a system can be used to implement the transitivity and redundancy conditions required for dimensional self-calibration so that only a single scaling input is required. The approach is verified by a series of simulations and experiments to demonstrate repeatable self-calibration of the axis to within 1 nm over a displacement range of 30 µm.

Combined H ∞ -feedback and eterative learning control design with application to nanopositioning systems

In this paper, a systematic design based on the robust control theory is developed for a microelectromechanical systems nanopositioning/probing device. The device is fabricated on a silicon-on-insulator substrate, and provides decoupled XY motion by using a parallel kinematics mechanism design. Each axis of the device is actuated by linear comb-drives and the corresponding displacements are sensed by separate comb structures. To improve the sensing resolution, the sensing and driving combs are electrically isolated. The nonlinear dynamic model between the actuation voltage and the sensed displacement will increase the complexity of model identification and control design. We circumvent the nonlinear model by redefining the input and output (I/O) signals during the model definition and identification, which results in linear and time-invariant models. A dynamical model of the system is identified through experimental input-output frequency-domain identification. The implemented H∞ control design achieves a significant improvement over the response speed, where the bandwidths from the closed-loop sensitivity and complementary sensitivity functions, respectively, are 68 and 74 Hz. When compared to open-loop characteristics, enhancement in reliability and repeatability (robustness to uncertainties) as well as noise attenuation (by over 12%) is demonstrated through this design.