Micro/nano manipulation for both mechanical and biological structures is currently a popular research field. To protect small-scale structures and acquire their mechanical properties, a micro-scale force sensor is needed. This paper focuses on reviewing the research on non-contact micro-force sensor parts that can be integrated in this manipulation system. The content involves the structure, working principle, resolution and sensitivity of different force sensor parts, including electrical and optical force sensors. The electrical force sensors include piezoresistive, piezoelectric, capacitive, electrothermal and strain gauge-based types; while the optical force sensors focus on but are not restricted to the optical fiber-based force sensors and the vision-based sensing systems. All of these sensors are analysed and compared. Electrical force sensors are currently widely used but are restricted by the sensing properties and size; optical force sensors have high sensitivity, small structure and anti-electromagnetic-interference properties, but they are hardly applied in micro/nano manipulation systems for force measurement. As a result, optical force sensors may become the new generation of sensors that can be integrated with micro/nano manipulation systems.

Recent advances in non-contact force sensors used for micro/nano manipulation

Limitations of the pinhole method and astigmatic defocus detection have difficulties in determining the direction of defocus and a restricted linear correction range. Here, a distance-measuring approach based on the laser triangulation principle is proposed with a corresponding mathematical model to overcome these problems and to satisfy the requirements of an industrial thin-film transistor liquid-crystal display (TFT-LCD) inspection microscope system in active auto-focus applications. The approach combines infrared light at a wavelength of 808 nm with visible light. The light reflected from the surface of the object reaches a CCD camera and forms a spot via a set of optical devices. To control a PZT to achieve real-time auto-focusing, a Gaussian curve fitting method is used to process the spot information with the presented mathematical model giving the relationship between the detection value and the defocus value focus error signal (FES). The preliminary experiments with a $50\times $ objective lens show that the measured values are consistent with the theoretical values, have good linearity and possess a focusing accuracy of 0.2 $\mu \text{m}$ within $\pm 30~\mu \text{m}$ of the focal plane. The analysis of the experimental results proves the feasibility of using this method in industrial applications. Compared with the traditional method of microscope focus correction, this method has the advantages of high accuracy, good linearity, and fast focus speed for the actual requirements of industrial inspection processes. This method has been applied to the circuit board component defect detection in our laboratory.

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A Novel Auto-Focus Method for Image Processing Using Laser Triangulation

Compliant Mechanisms (CMs) are currently employed in several engineering applications requiring high precision and reduced number of parts For a given mechanism topology, CM analysis and synthesis may be developed resorting to the Pseudo–Rigid Body (PRB) method, in which the behavior of flexible members is approximated via a series of rigid links connected by spring-loaded kinematic pairs From a CM analysis standpoint, the applicability of a generic PRB model requires the determination of the kinematic pairs’ location and the stiffness of a set of generalized springs In parallel, from a design standpoint, a PRB model representing the kinetostatic behavior of a flexible system should allow to compute the flexures’ characteristics providing the desired compliance In light of these considerations, this paper describes a Computer-Aided Design/Engineering (CAD/CAE) framework for the automatic derivation of accurate PRB model parameters, on one hand, and for the shape optimization of complex-shape flexures comprising out-of-plane displacements and distributed compliance The method leverages on the modelling and simulation capabilities of a parametric CAD (ie PTC Creo) seamlessly connected to a CAE tool (ie RecurDyn), which provides built-in functions for modelling the motion of flexible members The method is initially validated on an elementary case study taken from the literature Then, an industrial case study, which consists of a spatial crank mechanism connected to a fully-compliant four-bar linkage is discussed At first, an initial sub-optimal design is considered and its PRB representation is automatically determined Secondly, on the basis of the PRB model, several improved design alternatives are simulated Finally, the most promising design solution is selected and the dimensions of a flexure with non-trivial shape (ie hybrid flexure) is computed This technique, which combines reliable numerical results to the visual insight of CAD/CAE tools, may be particularly useful for analyzing/designing spatial CMs composed of complex flexure topologies

A CAD/CAE integration framework for analyzing and designing spatial compliant mechanisms via pseudo-rigid-body methods

Beam-based Compliant Mechanisms (CMs) are increasingly studied and implemented in precision engineering. Straight beams with uniform cross section are the basic modules in several design concepts, which can be deemed as standard CMs. Their behavioral analysis can be addressed with a large variety of techniques, including the Euler–Bernoulli beam theory, the Pseudo-Rigid Body (PRB) method, the beam constraint model and the discretization-based methods. This variety is unquestionably reduced when considering nonstandard CMs, namely design problems involving special geometries, such as curve/spline beams, variable section beams, nontrivial shapes and contact pairs. The 3D Finite Element Analysis (FEA) provides accurate results but its high computational cost makes it inappropriate for optimization purposes. This work compares the potentialities of computationally efficient modeling techniques (1D FEA, PRB method and chained-beam constraint model), focusing on their applicability in nonstandard planar problems. The cross-axis flexural pivot is used as a benchmark in this research due to its high configurable behavior and wide range of applications. In parallel, as an attempt to provide an easy-to-use environment for CM analysis and design, a multi-purpose tool comprising Matlab and a set of modern Computer-Aided Design/Engineering packages is presented. The framework can implement different solvers depending on the adopted behavioral models. Summary tables are reported to guide the designers in the selection of the most appropriate technique and software framework. Lastly, efficient design procedures that allow to configure nonstandard beam-based CMs with prescribed behavior are examined with two design examples.

An Overview of Procedures and Tools for Designing Nonstandard Beam-Based Compliant Mechanisms

Compliant kaleidocycles can be widely used in a variety of applications, including deployable structures, origami structures, and metamorphic robots, due to their unique features of continuous rotatability and multistability. Inspired by origami kaleidocycles, a type of symmetric multistable compliant mechanism with an arbitrary number of units is presented and analyzed in this paper. First, the basic dimension constraints are developed based on mobility analysis using screw theory. Second, the kinematic relationships of the actual rotation angle are obtained. Third, a method to determine the number of stabilities and the position of stable states, including the solution for the parameterized boundaries of stable regions, is developed. Finally, experimental platforms are established, and the validity of the proposed multistable mechanisms is verified.

Origami Kaleidocycle-Inspired Symmetric Multistable Compliant Mechanisms

This study presents a method for micro-motion detection of the three-degrees-of-freedom (3-DOF; x, y, θz) precision positioning stage (PPS) based on iterative optimized template matching (IOTM). In this method, a micro-vision system (MVS) is constructed and employed to capture magnified images of the measured PPS’s surface with high quality. In addition, an efficient and accurate IOTM algorithm, which includes a pyramid hierarchical matching step for generating the initial guess and an iterative searching step for 3-DOF fine matching, is proposed to detect the micro-motion of the 3-DOF PPS. The simulation results show that the locating accuracy of the translation component (TC) and rotation component of this algorithm can respectively reach 0.01 pixels and 0.01 deg when the image quality is high and the initial guess is close to the real location. Measurement tests of a nano-PPS verify that the proposed method is practical and effective for 3-DOF micro-motion detection and the absolute accuracy of the TC of the MVS can easily reach the nanometer level.

Micro-motion detection of the 3-DOF precision positioning stage based on iterative optimized template matching.

Calibration for scanning electron microscope (SEM) based nanorobotic manipulation systems is important and difficult. Most current calibration methods are cumbersome because they require customized high precision calibration boards and repeated calibration procedures in different magnifications. This paper presents a convenient magnification-continuous calibration method with high precision for SEM-based nanorobotic manipulation systems. The projection matrix containing a continuous magnification factor is obtained by modifying the affine camera model. This facilitates the simplification of the parameter computing process. Movement features are used to align the moving axes of micropositioning stages and calibrate the system, which benefits for the realization of efficient automatic calibration. Three experiments are carried out, and the results demonstrate that the proposed method is effective and practical for calibrating SEM-based nanorobotic manipulation systems under a wide range of continuous magnifications. Experiments also confirm that high precision measurements can be conducted in different magnifications with only once calibration and the relative error is within 1%.

A magnification-continuous calibration method for SEM-based nanorobotic manipulation systems

Defocus and astigmatism can lead to blurred images and poor resolution. This paper presents a simplified method for focusing and astigmatism correction of a scanning electron microscope (SEM). The method consists of two steps. In the first step, the fast Fourier transform (FFT) of the SEM image is performed and the FFT is subsequently processed with a threshold to achieve a suitable result. In the second step, the threshold FFT is used for ellipse fitting to determine the presence of defocus and astigmatism. The proposed method clearly provides the relationships between the defocus, the astigmatism and the direction of stretching of the FFT, and it can determine the astigmatism in a single image. Experimental studies are conducted to demonstrate the validity of the proposed method.

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A simplified focusing and astigmatism correction method for a scanning electron microscope

Edge determination improvement of scanning electron microscope images by inpainting and anisotropic diffusion for measurement and analysis of microstructures

This paper develops a robust edge-based template matching algorithm for displacement measurement of compliant mechanisms under a scanning electron microscope (SEM). The algorithm consists of three steps. First, the Sobel gradient operator and a self-adaptive segment strategy are used to establish the shape model in which the gradient directions of the object's edge points are calculated. Second, a similarity criterion based on image gradients that is robust to illumination change and image noise is utilized for template matching to obtain the coarse results. The third step is to refine the matching results by using an orientation-guided subpixel interpolation strategy. A series of simulations is conducted, and the results show that the proposed algorithm enjoys great robustness against strong image noise and gray-value fluctuation, as well as small rotations and background interferences, and thus is suitable for processing SEM images of compliant mechanisms. Finally, the application of the proposed algorithm in the measurement of the spring constant of the flexure hinges with a straight beam form under a SEM is demonstrated.

Yihua Lu

Papers

Micro-motion detection of the 3-DOF precision positioning stage based on iterative optimized template matching.

A magnification-continuous calibration method for SEM-based nanorobotic manipulation systems

A simplified focusing and astigmatism correction method for a scanning electron microscope

Edge determination improvement of scanning electron microscope images by inpainting and anisotropic diffusion for measurement and analysis of microstructures

A robust edge-based template matching algorithm for displacement measurement of compliant mechanisms under scanning electron microscope