A 2 degree-of-freedom SOI-MEMS translation stage with closed loop positioning

This research contains the design, analysis, fabrication, and characterization of a closed loop XY micro positioning stage. The XY micro positioning stage is developed by adapting parallel-kinematic mechanisms, which have been widely used for macro and meso scale positioning systems, to silicon-based micropositioner. Two orthogonal electrostatic comb drives are connected to moving table through 4-bar mechanism and independent hinges which restrict unwanted rotation in 2-degree-of-freedom translational stage. The XY micro positioning stage is fabricated on SOI wafer with three photolithography patterning processes followed by series of DRIE etching and HF etching to remove buried oxide layer to release the end-effector of the device. The fabricated XY micro positioning stage is shown in Fig1 with SEM images. The device provides a motion range of 20 microns in each direction at the driving voltage of 100V. The resonant frequency of the XY stage under ambient conditions is 811 Hz with a high quality factor of 40 achieved from parallel kinematics. The positioning loop is closed using a COTS capacitance-to-voltage conversion IC and a PID controller built in D-space is used to control position with an uncertainty characterized by a standard distribution of 5.24nm and a approximate closed-loop bandwidth of 27Hz. With the positioning loop, the rise time and settling time for closed-loop system are 50ms and 100ms. With sinusoidal input of ω=1Hz, the maximum phase difference of 108nm from reference input is obtained with total motion range of 8μm

Design and computational optimization of a flexure-based XY nano-positioning stage

This thesis presents the design and computational optimization of a two-axis nano-positioning stage. The devised stage relies on double parallelogram flexure bearings with under-constraint eliminating linkages to enable motion in the primary degrees-of-freedom. The structural parameters of the underlying flexures were optimized to provide a large-range and high bandwidth with sub-micron resolution while maintaining a compact size. A finite element model was created to establish a functional relationship between the geometry of the flexure elements and the stiffness behavior. Then, a neural network was trained from the simulation results to explore the design space with a low computational expense. The neural net was integrated with a genetic algorithm to optimize the design of the flexures for compactness and dynamic performance. The optimal solutions resulted in a reduction of stage footprint by 14% and an increase in the first natural frequency by 75% relative to a baseline design, all while preserving the same 50mm range in each axis with a factor of safety of 2. This confirms the efficacy of the proposed approach in improving stage performance through an optimization of its constituent flexures.Mechanical Engineerin

PKM mechatronic clamping adaptive device

This study proposes a novel adaptive fixturing device based on active clamping systems for smart micropositioning of thin-walled precision parts. The modular architecture and the structure flexibility make the system suitable for various industrial applications. The proposed device is realized as a Parallel Kinematic Machine (PKM), opportunely sensorized and controlled, able to perform automatic error-free workpiece clamping procedures, drastically reducing the overall fixturing set-up time. The paper describes the kinematics and dynamics of this mechatronic system. A first campaign of experimental trails has been carried out on the prototype, obtaining promising results

Design and control methodology of a 3-DOF flexure-based mechanism for micro/nano-positioning

A 3-DOF (X–Y–θZ) planar flexure-based mechanism is designed and monolithically manufactured using Wire Electro-Discharge Machining (WEDM) technology. The compact flexure-based mechanism is directly driven by three piezoelectric actuators (PZTs) through decoupling mechanisms. The orthogonal configuration in the x and y directions can guarantee the decoupling translational motion in these axes. The rotational motion and translational displacement in the x direction can be decoupled by controlling the piezoelectric actuators in the x axis with the same displacement values in same and opposite motion directions, respectively. The static and dynamic models of the developed flexure-based mechanism have been developed based on the pseudo-rigid-body model methodology. The mechanical design optimization is conducted to improve the static and dynamic characteristics of the flexure-based mechanism. Finite Element Analyses (FEA) are also carried out to verify the established models and optimization results. A novel hybrid feedforward/feedback controller has been provided to eliminate/reduce the nonlinear hysteresis and external disturbance of the flexure-based mechanism. Experimental testing has been performed to examine the dynamic performance of the developed flexure-based mechanism

Design, Development and Implementation of the Position Estimator Algorithm for Harmonic Motion on the XY Flexural Mechanism for High Precision Positioning

This article presents a novel concept of the position estimator algorithm for voice coil actuators used in precision scanning applications. Here, a voice coil motor was used as an actuator and a sensor using the position estimator algorithm, which was derived from an electro-mechanical model of a voice coil motor. According to the proposed algorithm, the position of coil relative to the fixed magnet position depends on the current drawn, voltage across coil and motor constant of the voice coil motor. This eliminates the use of a sensor that is an integral part of all feedback control systems. Proposed position estimator was experimentally validated for the voice coil actuator in integration with electro-mechanical modeling of the flexural mechanism. The experimental setup consisted of the flexural mechanism, voice coil actuator, current and voltage monitoring circuitry and its interfacing with PC via a dSPACE DS1104 R&D microcontroller board. Theoretical and experimental results revealed successful implementation of the proposed novel algorithm in the feedback control system with positioning resolution of less than ±5 microns at the scanning speed of more than 5 mm/s. Further, proportional-integral-derivative (PID) control strategy was implemented along with developed algorithm to minimize the error. The position determined by the position estimator algorithm has an accuracy of 99.4% for single direction motion with the experimentally observed position at those instantaneous states

Characterization and System Identification of XY Flexural Mechanism Using Double Parallelogram Manipulator for High Precision Scanning

This article represents modeling of double parallelogram flexural manipulator derived from basic classical mechanics theory. Fourth order vibration wave equation is used for mathematical modeling and its performance is determined for step input and sinusoidal forced input. Static characterization of DFM is carried out to determine stiffness and force deflection characteristics over the entire motion range and dynamic characteristics is carried out using Transient response and Frequency response. Transient response is determined using step input to DFM which gives system properties such as damping, rise time and settling time. These parameters are then compared with theoretical model presented previously. Frequency response of DFM system gives characteristics of system with different frequency inputs which is used for experimental modeling of DFM device. Here, Voice Coil Motor is used as Actuator and optical encoder is used for positioning sensing of motion stage. It is noted that theoretical model is having 5% accuracy with experimental results. To achieve better position and accuracy, PID and LQR (Linear Quadratic Regulator) implementation was carried out on experimental model. PID gains are optimally tuned by using Ziegler Nichols approach. PID control is implemented experimentally using dSPACE DS1104 microcontroller and Control Desk software. Experimentally, it is observed that positioning accuracy is less than 5 μm. Further multiple DFM blocks are arranged for developing XY flexural mechanism and static characterization was carried out on it. The comparison of experimental and FEA results for X-direction and Y-direction is presented at end of paper

Integration of shape memory alloy for microactuation

Shape memory alloy (SMA) actuators in microelectromechanical system (MEMS) have a broad range of applications. The alloy material has unique properties underlying its high working density, simple structures, large displacement and excellent biocompatibility. These features have led to its commercialization in several applications such as micro-robotics and biomedical areas. However, full utilization of SMA is yet to be exploited as it faces various practical issues. In the area of microactuators in particular, fabricated devices suffer from low degrees of freedom (DoF), complex fabrication processes, larger sizes and limited displacement range. This thesis presents novel techniques of developing bulk-micromachined SMA microdevices by applying integration of multiple SMA microactuators, and monolithic methods using standard and unconventional MEMS fabrication processes. The thermomechanical behavior of the developed bimorph SMA microactuator is analyzed by studying the parameters such as thickness of SMA sheet, type and thickness of stress layer and the deposition temperature that affect the displacement. The microactuators are then integrated to form a novel SMA micromanipulator that consists of two links and a gripper at its end to provide three-DoF manipulation of small objects with overall actuation x- and y- axes displacement of 7.1 mm and 5.2 mm, respectively. To simplify the fabrication and improve the structure robustness, a monolithic approach was utilized in the development of a micro-positioning stage using bulk-micromachined SMA sheet that was fabricated in a single machining step. The design consisted of six spring actuators that provided large stage displacement range of 1.2 mm and 1.6 mm in x- and y-axes, respectively, and a rotation of 20° around the z-axis. To embed a self-sensing functionality in SMA microactuators, a novel wireless displacement sensing method based on integration of an SMA spiral-coil actuator in a resonant circuit is developed. These devices have the potential to promote the application of bulk-micromachined SMA actuator in MEMS area

Development of a piezo-driven 3-DOF stage with T-shape flexible hinge mechanism

This paper presents a 3-DOF (Degree of freedom) stage with T-shape flexible hinge mechanism for the applications in the precision measurement equipments and micro/nano manipulation systems. The stage is driven by three piezoelectric actuators (PEAs) and guided by a flexible hinge based mechanism with three symmetric T-shape hinges. The proposed T-shape flexible hinge mechanism can provide excellent planar motion capability with high stability, and thus guarantee the outstanding dynamics characteristics. The theoretical modeling of the stage was carried out and the stiffness and the dynamic resonance frequency have been obtained. The kinematic model of the 3-DOF stage was established and the workspace has been analyzed. The characteristics of the stage were investigated using finite element analysis (FEA). Experiments were conducted to examine the performance of the stage, through this stage, X-axis translational motion stroke of 6.9 µm, Y-axis translational motion stroke of 8.5 µm and rotational motion stroke along Z-axis of 289 µrad can be achieved. A hybrid feedforward/feedback control methodology has been proposed to eliminate the nonlinear hysteresis, the trajectory tracking performances and to reduce external disturbance of the 3-DOF stage

Affordable flexible hybrid manipulator for miniaturised product assembly

Miniaturised assembly systems are capable of assembling parts of a few millimetres in size with an accuracy of a few micrometres. Reducing the size and the cost of such a system while increasing its flexibility and accuracy is a challenging issue. The introduction of hybrid manipulation, also called coarse/fine manipulation, within an assembly system is the solution investigated in this thesis. A micro-motion stage (MMS) is designed to be used as the fine positioning mechanism of the hybrid assembly system. MMSs often integrate compliant micro-motion stages (CMMSs) to achieve higher performances than the conventional MMSs. CMMSs are mechanisms that transmit an output force and displacement through the deformation of their structure. Although widely studied, the design and modelling techniques of these mechanisms still need to be improved and simplified. Firstly, the linear modelling of CMMSs is evaluated and two polymer prototypes are fabricated and characterised. It is found that polymer based designs have a low fabrication cost but not suitable for construction of a micro-assembly system. A simplified nonlinear model is then derived and integrated within an analytical model, allowing for the full characterisation of the CMMS in terms of stiffness and range of motion. An aluminium CMMS is fabricated based on the optimisation results from the analytical model and is integrated within an MMS. The MMS is controlled using dual-range positioning to achieve a low-cost positioning accuracy better than 2µm within a workspace of 4.4×4.4mm2. Finally, a hybrid manipulator is designed to assemble mobile-phone cameras and sensors automatically. A conventional robot manipulator is used to pick and place the parts in coarse mode while the aluminium CMMS based MMS is used for fine alignment of the parts. A high-resolution vision system is used to locate the parts on the substrate and to measure the relative position of the manipulator above MMS using a calibration grid with square patterns. The overall placement accuracy of the assembly system is ±24µm at 3σ and can reach 2µm, for a total cost of less than £50k, thus demonstrating the suitability of hybrid manipulation for desktop-size miniaturised assembly systems. The precision of the existing system could be significantly improved by making the manipulator stiffer (i.e. preloaded bearings…) and adjustable to compensate for misalignment. Further improvement could also be made on the calibration of the vision system. The system could be either scaled up or down using the same architecture while adapting the controllers to the scale.Engineering and Physical Sciences Research Council (EPSRC