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

Digital Microrobotics based on bistable modules : Design of a non-redundant digital micropositioning robot.

International audienceHigh precision manipulation becomes a recurrent need in micro or nanoscale. Microrobots based on active material were designed to perform micromanipulation tasks in various environments such as microrobotic stations or electronic microscopes (SEM, TEM). These active materials are used to generate proportional actuation, but show some drawbacks we want to avoid (non linearity, integration of sensors, . . . ). In this paper we propose a new type of microrobot, called digital microrobot. It is based on the use of bistable modules (Fig. 1), and generates a discrete workspace. This microrobot can be used in open-loop mode and gets rid of bulky and expensive instruments and sensor integration. Moreover, no external energy is required to maintain the microrobot in a given position. The study presented in this paper is dedicated to the design of the robotic structure in order to generate a desired workspace

A novel voice coil motor-driven compliant micropositioning stage based on flexure mechanism

This paper presents a 2-degrees of freedom flexure-based micropositioning stage with a flexible decoupling mechanism. The stage is composed of an upper planar stage and four vertical support links to improve the out-of-plane stiffness. The moving platform is driven by two voice coil motors, and thus it has the capability of large working stroke. The upper stage is connected with the base through six double parallel four-bar linkages mechanisms, which are orthogonally arranged to implement the motion decoupling in the x and y directions. The vertical support links with serially connected hook joints are utilized to guarantee good planar motion with heavy-loads. The static stiffness and the dynamic resonant frequencies are obtained based on the theoretical analyses. Finite element analysis is used to investigate the characteristics of the developed stage. Experiments are carried out to validate the established models and the performance of the developed stage. It is noted that the developed stage has the capability of translational motion stroke of 1.8 mm and 1.78 mm in working axes. The maximum coupling errors in the x and y directions are 0.65% and 0.82%, respectively, and the motion resolution is less than 200 nm. The experimental results show that the developed stage has good capability for trajectory tracking

A flexure-based kinematically decoupled micropositioning stage with a centimeter range dedicated to micro/nano manufacturing

Precision positioning stages with large strokes and high positioning accuracy are attractive for high-performance micro/nano manufacturing. This paper presents the dynamic design and characteristic investigation of a novel XY micropositioning stage. Firstly, the mechanism of the stage was introduced. The XY stage was directly driven by two linear motors, and the X- and Y- axes kinematic decoupling was realized through a novel flexible decoupling mechanism based on flexure hinges and preloaded spring. The dynamic model of the XY stage was established, and the influences of the rotational stiffness of the flexure hinge and the initial positions of the working table on the dynamic rotation of the positioning stage were investigated. The stiffness and geometric parameters of the flexure hinges were determined at the condition that the angular displacements of the working table were within ±0.5° with a motion stroke of ±25 mm. Finally the stage performance was investigated through simulation and experiments, the X- and Y-axes step responses, the rotation angular and positioning accuracy of the stage were obtained. The results show that the stage exhibits good performance and can be used for micro/nano manufacturing

A novel actuator-internal micro/nano positioning stage with an arch-shape bridge type amplifier

This paper presents a novel actuator-internal two degree-of-freedom (2-DOF) micro/nano positioning stage actuated by piezoelectric (PZT) actuators, which can be used as a fine actuation part in dual-stage system. To compensate the positioning error of coarse stage and achieve a large motion stroke, a symmetrical structure with an arch-shape bridge type amplifier based on single notch circular flexure hinges is proposed and utilized in the positioning stage. Due to the compound bridge arm configuration and compact flexure hinge structure, the amplification mechanism can realize high lateral stiffness and compact structure simultaneously, which is of great importance to protect PZT actuators. The amplification mechanism is integrated into the decoupling mechanism to improve compactness, and to produce decoupled motion in X- and Y- axes. An analytical model is established to explore the static and dynamic characteristics, and the geometric parameters are optimized. The performance of the positioning stage is evaluated through finite element analysis (FEA) and experimental test. The results indicate that the stage can implement 2-DOF decoupled motion with a travel range of 55.4×53.2 μm2, and the motion resolution is 8 nm. The stage can be used in probe tip-based micro/nano scratching

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

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

Micro motion stages with flexure hinges-design and control

The developments in micro and nano technologies brought the need of high precision micropositioning stages to be used in micro/nano applications such as cell manipulation, surgery, aerospace, micro fluidics, optical systems, micromachining and microassembly etc. Micro motion stages with flexible joints called compliant mechanisms are built to provide the needed accuracy and precision. This thesis aims to build compliant planar micro motion stages using flexure hinges to be used as micropositioning devices in x-y directions by applying new control methods. First 3- RRR planar parallel kinematic structure is selected which is also popular in the literature. Then the mechanism is developed to have a new structure which is a 3-PRR mechanism. The necessary geometric parameters are selected by using Finite Element Analysis (FEA). The displacement, stress and frequency behaviors of the mechanisms are compared and discussed. Modeling of the flexure based mechanisms is also studied for 3-PRR compliant stage by using Kinetostatic modeling method which combines the compliance calculations of flexure hinges with kinematics of the mechanism. Piezoelectric actuators and optical 2d position sensor which uses a laser source are used for actuation and measurement of the stages. After the experimental studies it's seen that the results are not compatible with FEA because of the unpredictable errors caused by manufacturing and assembly. We have succeeded to eliminate those errors by implementing a control methodology based on Sliding Mode Control with Disturbance Observer which is also based on Sliding Mode Control using linear piezoelectric actuator models. Finally, we have extracted experimental models for each actuation direction of the stage and used those models instead of piezoelectric actuator models which lowered our errors in the accuracy of our measurement and ready to be used as a high precision micro positioning stage for our micro system applications

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