Showing papers by "Benliang Zhu published in 2021"

A Review of Computer Microvision-Based Precision Motion Measurement: Principles, Characteristics, and Applications

Abstract: Microengineering/nanoengineering is an emerging field that enables engineering and scientific discoveries in the microworld. As an effective and powerful tool for automation and manipulation at small scales, precision motion measurement by computer microvision is now broadly accepted and widely used in microengineering/nanoengineering. Unlike other measurement methods, the vision-based techniques can intuitively visualize the measuring process with high interactivity, expansibility, and flexibility. This article aims to comprehensively present a survey of microvision-based motion measurement from the collective experience. Working principles of microvision systems are first introduced and described, where the hardware configuration, model calibration, and motion measurement algorithms are systematically summarized. The characteristics and performances of different microvision-based methods are then analyzed and discussed in terms of measurement resolution, range, degree of freedom, efficiency, and error sources. Recent advances of applications empowered by the developed computer microvision-based methods are also presented. The review can be helpful to researchers who engage in the development of microvision-based techniques and provide the recent state and tendency for the research community of vision-based measurement, manipulation, and automation at microscale/nanoscale.

An 89-line code for geometrically nonlinear topology optimization written in FreeFEM

Abstract: Topology optimization has emerged as a powerful tool for structural configuration design. To further promote the development of topology optimization, many computer programs have been published for educational purposes over the past decades. However, most of the computer programs are constructed based on a linear assumption. This paper presents an 89-line code for nonlinear topology optimization written in FreeFEM based on the popular SIMP (solid isotropic material with penalization) method. Excluding thirteen lines which are used for explanation, only 76 lines are needed for the initialization of the design parameters, nonlinear finite element analysis, sensitivity calculation, and updated design variables. Different design problems can be solved by modifying several lines in the proposed program. The complete program is given in the Appendix and is intended for educational purposes only.

Explicit structural topology optimization using moving wide Bezier components with constrained ends

Abstract: This paper presents a structural topology optimization method using moving wide Bezier components with constrained ends. In the proposed method, components which are determined by using Bezier curves with a certain width are regarded as design units. These wide Bezier curves are represented by using level set functions. The control points of such wide Bezier curves are taken as design variables. In addition, based on that principle, in order to form one single connected load-bearing structure, the loading, supporting, and/or some other functional interactions must be connected. This is achieved by constraining the ends of the utilized wide Bezier curves which can essentially avoid any structurally invalid designs and thereby smooth the optimization process. The validity of the proposed method is tested on the stiffness and the compliant mechanisms design problem.

Pose Sensing and Servo Control of the Compliant Nanopositioners Based on Microscopic Vision

Abstract: This article presents new pose sensing and servo control techniques for the compliant nanopositioners (CNPs) based on optical microscopic vision. A visual pose tracking algorithm (VPTA) and a visual servo positioning scheme (VSPS) that both utilize iterative template matching are presented. In the VPTA, to realize pose sensing of the CNPs with high performance, an improved Gaussian–Newton optimization method combined with an adaptive penalty strategy is developed. In the VSPS, to realize robust and flexible control of the CNPs, a velocity controller that directly uses the gray value of the template to control the CNP is designed. Simulations and experiments are performed to demonstrate the performance of the proposed method. Results show that the VPTA can achieve pose tracking of the three-degree-of-freedom ( $x$ , $y$ , $\theta$ ) CNPs at a frame rate of hundred hertz, and the dynamic tracking errors are smaller than 100 nm, 160 nm, and 40 $\mu {\text{rad}}$ in the $x$ -, $y$ -, and $\theta$ -axes, respectively. Moreover, by using the proposed VSPS, task-based nanopositioning can be easily realized without extracting features of the object, and the obtained stable positioning accuracies are better than 30 nm, 33 nm, and 3 $\mu {\text{rad}}$ in the $x$ -, $y$ -, and $\theta$ -axes, respectively.

Topology optimization of flexure hinges with a prescribed compliance matrix based on the adaptive spring model and stress constraint

Abstract: This paper focuses on the configuration design of flexure hinges with a prescribed compliance matrix and preset rotational center position. A new method for the topology optimization of flexure hinges is proposed based on the adaptive spring model and stress constraint. The hinge optimization model is formulated by maximizing the bending displacement with a spring while optimizing the compliance matrix to a prescribed value. To avoid numerical instability, an artificial spring is used as an auxiliary calculation, and a new strategy is developed for adaptively adjusting the spring stiffness according to the prescribed compliance matrix. The maximum stress of flexure hinge is limited by using a normalized P-norm of the effective von Mises stress, and a position constraint of rotational center is proposed to predetermine the position of the rotational center. In addition, to reduce the error of the stress measurement, a simple but effective filtering method is presented to obtain a complete black-and-white design. Numerical examples are used to verify the proposed method. Topology results show that the obtained flexure hinges have the prescribed compliance matrix and preset rotational center position while also meeting the stress requirements.

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

Abstract: 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.

Multi-material topology optimization of large-displacement compliant mechanisms considering material-dependent boundary condition:

Abstract: Multi-material compliant mechanisms design enables potential design possibilities by exploiting the advantages of different materials. To satisfy mechanical/thermal impedance matching requirements,...

Design of a Variable Compliance Mechanism with Changeable Compliance Orientation

Abstract: Variable compliance mechanisms are considered as an effective way for interaction with changeable environments. Existing designs of variable compliance mechanisms can only change the amplitude of compliance rather than the orientation of compliance. In this paper, a novel hybrid mechanism is designed to realize changeable compliance orientation in a large range. The mechanical structure and working principle of the designed mechanism are firstly presented. Then, the closed-form relationship between compliance orientation and configuration of the designed mechanism is analyzed. Spherical coordinates are used to characterize and evaluate the orientation of compliance. Theoretical analysis shows that the orientation of compliance can be changed in a large range spatially. Finite element analysis is also performed to verify the theoretical model. It shows that the orientations of deformation during simulations are close to the theoretical compliance orientations. Under unchanged loading conditions, a large change in deformation orientation can be achieved by changing the mechanism’s configuration. This indicates that the designed mechanism can change the compliance orientation in a large range.

Design of Flexure Hinges Using Geometrically Nonlinear Topology Optimization

Abstract: Topology optimization has been employed for the configurational design of flexure hinges under linear assumption in recent years. This paper presents a method for the design of flexure hinges with large displacements in which the nonlinear topology optimization is adopted. An optimization model is developed based on the spring model. The objective function is formulated by minimizing the stiffness in the desired direction. A rotational index is proposed and serves as one of the constraints for accomplishing the high precision revolute requirement. A symmetry constraint is employed to improve the practicability of the optimized results. A minimal length scale control technique is adopted to avoid point flexure issue. Several numerical results are performed to demonstrate the effectiveness of the proposed method.

Kinetostatic Modeling of Piezoelectric Displacement Amplifiers Based on Matrix Displacement Method

Abstract: Displacement amplification ratio and input stiffness modeling of three types of piezoelectric displacement amplifiers (PDAs) were investigated in this paper. The main feature is that we further improved the accuracy of matrix displacement model (MDM) by setting a node on both input and output points, and simplified modeling process of the MDM by utilizing axial symmetry of PDAs. Firstly, we deduced the stiffness matrix of the flexure element based on the general flexure hinge’s compliance formulas. Then, we established the MDM of a PDA by discretizing a displacement amplifier into flexure elements and assembling element stiffness matrices. The finite element method was employed to verify the superiority of presented model and to compare with typical analytical models and conventional MDMs. The results show that the presented model of both the displacement amplification ratio and input stiffness has better accuracy on the whole, thanks to consider deformation of both the input and output points during modeling and abandons considering input and output ends as a lumped mass.