Micro-positioning Applications Research Articles

Design, fabrication, and testing of flexurally amplified piezo actuator

Multilayer piezo actuators have typical characteristics of micro-displacement with high stiffness and well suitable for precise, quick positioning applications. However, the performance is insufficient for positioning devices demanding large displacements. Hence numerous designs of mechanical amplifier structure based on the use of flexural hinges have emerged. The present work describes the design, fabrication, and testing of a Flexurally Amplified Piezo actuator for micro-positioning applications. A Rhombic flexural amplifier is proposed to amplify the displacement of six multilayer piezo actuators. First, the flexural amplifier is analyzed for the geometrical amplification, in-out stiffness. Followed by the fabrication using spring steel material in wire cut Electro Discharge Machine. The fabricated prototype is bonded with multilayer piezo actuators by structural adhesive. The assembled system is called a Flexurally Amplified Piezo actuator. This system exhibited a nonlinear hysteresis behavior measured by the laser displacement sensor for the actuation voltage. Hence, an electromechanical model is developed to control the nonlinear hysteresis behavior of the Flexurally Amplified Piezo actuator using MATLAB® & SIMULINK® software by implementing the Prandtl Ishlinskii hysteresis equations. Open-loop tracking control experiments are conducted to verify the validity of the electromechanical model.

Stress self-sensing in Amplified Piezoelectric Actuators through a fully-coupled model of hysteresis

Piezoelectric actuators are among the most used devices for micro-positioning applications. Yet, their output displacement shows non-negligible hysteresis effects with respect to both the input voltage and the mechanical stress and, as a consequence, an accurate control system has to be designed, taking into account the mechanical stress measurement too. This task is usually addressed by exploiting external bulky force sensors, e.g. load cells. A novel stress self-sensing approach is proposed in this paper, which allows the stress estimation by simply exploiting the measurement of electrical voltage and current of the piezoelectric stacks. In particular, a thermodynamic consistent fully-coupled multi-input multi-output model of hysteresis is exploited. The method is applied for the first time to a commercial Amplified Piezoelectric Actuator with a crossbow-like amplification system. An experimental validation of the approach is proposed and discussed.

Experimental Hysteresis Identification and Micro-position Control of a Shape-Memory-Alloy Rod Actuator

In order to exhaustively exploit the high-level capabilities of shape memory alloys (SMAs), they must be applied in control systems applications. However, because of their hysteretic inherent, dilatory response, and nonlinear behavior, scientists are thwarted in their attempt to design controllers for actuators of such kind. The current study aims at developing a micro-position control system for a novel SMA rod actuator. To do so, the hysteretic behavior of the actuator was simulated in the form of a gray-box Wiener model. Based on the experimental training dataset obtained from the actuator, the hysteresis Wiener model was trained using a PSO algorithm. Afterwards that the identified hysteresis Wiener model was validated, the authors formed a model-in-the-loop (MIL) position control system. Next, a PSO algorithm was again set to find the best controller parameters regarding some performance criteria. At the end, implemented on the fabricated prototype (the experimental setup), the designed control system shared such excellent accuracy that makes the fabricated actuator amenable to micro-positioning applications.

Optimized cross-spring pivot configurations with minimized parasitic shifts and stiffness variations investigated via nonlinear FEA

ABSTRACTCompliant mechanisms are nowadays a well-established means of achieving ultra-high precision, albeit at the expense of complex kinematics with the presence of parasitic motions. Diverse design configurations of compliant rotational joints called cross-spring pivots are hence studied in this work by applying various analytical and numerical approaches. Depending on the required precision and loading conditions, the limits of applicability of the available analysis tools, validated with nonlinear finite element calculations tuned with experimental data reported in literature, are established. The variation of design parameters allows, in turn, establishing design configurations of the studied mechanism that allow attaining minimized parasitic shifts and slight variations of its rotational stiffness, even when a broad range of rotations and varying transversal loads are considered, creating thus the preconditions for their application in high-precision micropositioning applications.

Hysteresis Model of Magnetically Controlled Shape Memory Alloy Based on a PID Neural Network

Magnetically controlled shape memory alloys(MSMA) are a new kind of smart material that can be used in micro-displacement and micro-positioning applications. However, the hysteresis nonlinearity of this material is an obstacle to achieve high precision accuracy [1]. The hysteresis nonlinearity of MSMA can be described by the relationship between the input and output signal which is called hysteresis loop [2]. As shown in figure 1(a), hysteresis loops can be divided into major and minor hysteresis loops. The input and output signals have the same phase at the extrema and the phase of the output signal lags behind the input signal at all other times. A major hysteresis loop takes shape when the input signal rises from an initial value to a maximum value before decreasing to a minimum value (which is same as the initial value). Minor hysteresis loops occur when the input signal rises from a local minimum value (which is different from the overall minimum value) to a local maximum value (which is different from the overall maximum value) before decreasing to a local minimum value.

MODELLING A COMPLIANT-BASED PRECISE POSITIONING STAGE / AUKŠTO TIKSLUMO POZICIONAVIMO SISTEMOS MODELIAVIMAS TAIKANT BESIDEFORMUOJANČIUS MECHANIZMUS

The paper presents modelling precise dual axis flexure-based precision positioning systems for micro-positioning applications. The positioning system is featured with monolithic architecture, flexure-based joints and piezo stacks. Its workspace has been evaluated via analytical approaches. Amplification mechanism is optimally designed. The mathematical model of the positioning system has been derived and verified by resorting to finite element analysis (FEA). The established analytical and (FEA) models are helpful for optimizing reliable architecture and improving the performance of the positioning system. Santrauka Straipsnyje pristatomas dviejų ašių didelio tikslumo pozicionavimo sistemos su paketiniais pjezovykdikliais modeliavimas, taikant besideformuojančius vientiso kūno mechanizmus. Pozicionavimo sistemą sudaro besideformuojančio vientiso kūno mechanizmas ir paketiniai pjezovykdikliai. Besideformuojantis vientiso kūno mechanizmas norimam poslinkiui pasiekti buvo optimizuotas Solidworks Simulation programiniu paketu. Platformų poslinkiams apskaičiuoti sudarytas matematinis modelis, kurio patikimumas patikrintas baigtinių elementų metodu. Sudaryto matematinio modelio ir rezultatų, gautų baigtinių elementų metodu, skirtumai yra mažesni nei 5 %, todėl pasiūlyta modeliavimo metodika gali būti taikoma kuriant pozicionavimo sistemas su besideformuojančiais elementais.

Design and Characterization of a Flexible Micro-Displacement Manipulator

For its fast response, nanometer resolution, no backlash, no friction and bigger driving force, flexure hinge has been commonly used as a substitute for mechanical joints in the design of micro-displacement mechanisms used in vibration suppression and micro-positioning applications. However, inaccurate modeling of flexure hinges deteriorates the positioning accuracy. In this paper, a planar two-degree-of-freedom (DOF) parallel four-bar manipulator is designed with the intention of accurate flexure hinge modeling. A 1-DOF flexure hinge is considered, a static analysis and a dynamic analytical model of parallel four-bar manipulator is presented. Simulation result based on the finite element method is coincident to the analytic result. Based on the theoretical analysis, the experimental demonstration to study the performance of the manipulator is described, and experimental results are in close agreement with those predicted by the theoretical analysis.

A LOW COST MACRO-MICRO POSITIONING SYSTEM WITH SMA-ACTUATED MICRO STAGE

Macro-micro systems allow high-resolution positioning over greater ranges of operation that would be achievable with precision positioning systems. Piezoceramic actuators have established themselves as the principle technology for commercial micro-positioning applications, and the trend in research is to push the limits of resolution down to the nanometer and sub-nanometer scales. Other smart materials offer the potential for lightweight, continuous actuation over small ranges, and hence may be useful in micro-positioning applications. This work focuses on the potential for SMA actuators to enable low-cost micro-positioning. Compared to piezos, SMA offer longer range and lower actuation voltages, enabling lower-cost drive electronics and removing the need for costly precision mechanical amplification stages. A prototype single-axis macro-micro positioning system is described, with a macro range of 200 mm and relative positioning precision of better than 5 5μm. The micro stage is driven by an NM70 SMA actuator from NanoMuscle. Macro and micro stages are modelled and controllers developed, and experimental system performance is evaluated. The success of the system provides an inexpensive platform for the study of macro-micro positioning issues such as stage coupling, friction, and drive flexibility, as well as for the position control of SMA.

Multi-Degree-of-Freedom Precision Position Sensing and Motion Control Using Two-Axis Hall-Effect Sensors

This paper presents a novel precision position-sensing methodology using two-axis Hall-effect sensors, where the absolute multi-degree-of-freedom (DOF) positioning of a device above any magnet matrix is possible. Magnet matrices have a periodic magnetic field about each of its orthogonal axes, which can be modeled using Fourier series. This position-sensing methodology was implemented on a Halbach-magnet-matrix-based magnetic-levitation (maglev) stage. It enables unrestricted translational and rotational ranges in planar motions with a potential 6-DOF motion-measuring capability. A Gaussian least-squares differential-correction (GLSDC) algorithm was developed and implemented to estimate the maglev stage’s position and orientation in three planar DOFs from raw Hall-effect-sensor measurements. Experimental results show its position resolution of better than 10μm in translation and 100μrad in rotation. The maximum rotational range achieved so far is 16deg, a factor of 100 improvement of a typical laser interferometers’ rotational range of a few milliradians. Classical lead-lag compensators were designed and implemented on a digital signal processor (DSP) to close the control loop at a sampling frequency of 800Hz for the three planar DOFs using the GLSDC outputs. Calibration was performed by comparing the Hall-effect sensors’ outputs against the laser-interferometer readings, which improved the positioning accuracy by correcting the GLSDC error. The experimental results exhibit better than a micrometer repeatability. This multi-DOF sensing mechanism is an excellent cost-effective solution to planar micro-positioning applications with unrestricted three-axis travel ranges.