Analytical model of displacement amplification and stiffness optimization for a class of flexure-based compliant mechanisms

The paper formulates an analytical method for displacement and stiffness calculations of planar compliant mechanisms with single-axis flexure hinges. The procedure is based on the strain energy and Castigliano’s displacement theorem and produces closed-form equations that incorporate the compliances characterizing any analytically-defined hinge, together with the other geometric and material properties of the compliant mechanism. Displacement amplification, input stiffness and output stiffness calculations can simply be performed for any serial compliant mechanism. The class of amplifying compliant mechanisms that contain symmetric corner-filleted or circular flexure hinges is specifically addressed here. A parametric study of the mechanism performance is performed, based on the mathematical model, and an optimization procedure is proposed, based on Lagrange’s multipliers and Kuhn-Tucker conditions, which identifies the design vector that maximizes the performance of these flexure-based compliant mechanisms. Independent finite element simulation confirms the analytical model predictions.     

A novel design and fabrication of a micro-gripper for manipulation of micro-scale parts actuated by a bending piezoelectric

In this study, a novel micro-gripper using a piezoelectric actuator was designed and improved by the design of experiments (DOE) approach. Using a bending PZT actuator connected to the micro-gripper by a rigid wedge can be considered as a novel approach in this field. Almost all of the similar grippers in this category were former actuated by a piezo-stack which has some limitations and difficulties like fabrication in MEMS proportions. The basic design was borrowed from compliant mechanisms that are suitable for MEMS application and easy to manufacture in micro-scale because of the intrinsic integration characteristic. Since stress concentration is common in flexure hinge compliant mechanisms, our focus was to consider strength as an important factor in our design. Finite element analysis tools were used to implement the DOE based on two criteria; minimizing stress concentration and maximizing the output displacement in the micro-gripper structure as much as possible with the consideration of the total size of the gripper. The experiment was performed to validate the simulation results and experiment results agreed well with the simulation one. The slight geometrical discrepancy in significant portions of structure like flexure hinges partially contributes to the accumulated error between the simulation and the experiments.

     

Design of an auto-focusing actuator with a flexure-based compliant mechanism for mobile imaging devices

There is increasing consumer’s demand for high-quality and high-performance mobile imaging devices. In this paper, an auto-focusing (AF) actuator with a flexure hinge that uses the electromagnetic (EM) circuit of a voice coil motor was designed and evaluated. The flexure hinge was designed by using finite element analysis. The EM circuit was designed based on the structural stiffness of the device. The EM circuit was analyzed using the design of experiments procedure. Based on the results, the effective design parameters were selected, and improvements were made to the design. Finally, a prototype of the AF actuator was manufactured, and the feasibility and performance of the actuator with the flexure hinge were verified experimentally. The experimental results indicated that the proposed actuator performed adequately and satisfied the design requirements.     

Design and analysis of the precision-driven unit for nano-indentation and scratch test

This paper presents a kind of precision-driven unit consisting of the piezoelectric actuator and flexure hinge to realize precision motion of the indenter in a self-made indentation device. Two important parameters of the flexure hinge, thickness t$t$ and width w$w$, were analyzed via finite element method and the results showed that the output displacement was a monotonic decreasing function of thickness t$t$ and width w$w$. The stiffness was a monotonic increasing function of thickness t$t$ and width w$w$. But almost all the first-order modal frequencies of flexure hinges with different thickness t$t$ and width w$w$ were higher than 3800 Hz which indicated that flexure hinges had good stability at low frequency condition. Output performance of the unit was tested and analyzed. Experimental results showed that the average maximum output displacement was 12.88 μm when the voltage was 120 V and the resolution was about 0.537 μm/V. The hysteresis was very small and it was about 8.91%. At last, the designed unit was assembled on a self-made indentation device. Preliminary indentation experiments proved that the unit worked well. So, the piezoelectric mechanism can be used in the indentation device and it is beneficial to ensure the miniaturization and realize in situ indentation experiments in the SEM and TEM.     

Kinematic analysis of a translational 3-d.o.f. micro-parallel mechanism using the matrix method

In this paper, we applied the matrix method to kinematic analysis of our translational 3-d.o.f. micro-parallel mechanism for an instance of general flexure mechanisms. The matrix method has been well developed in architecture to analyze frame structures. We found that this method is well suited to such a flexure mechanism with circular notched hinges as our micro-parallel mechanism because it can be approximated to a Rahmen structure. Our matrix method can calculate a compliance matrix with less matrix nodes than the conventional finite element method. First, the compliance matrices of a circular notched hinge and some other beams are defined, and the coordinate transformations of the compliance matrix are introduced. Secondly, an analysis of our micro-parallel mechanism is demonstrated.     

Optimal design of a 3D-printed scaffold using intelligent evolutionary algorithms

Fabrication of three-dimensional structures has gained increasing importance in the bone tissue engineering (BTE) field. Mechanical properties and permeability are two important requirement for BTE scaffolds. The mechanical properties of the scaffolds are highly dependent on the processing parameters. Layer thickness, delay time between spreading each powder layer, and printing orientation are the major factors that determine the porosity and compression strength of the 3D printed scaffold.In this study, the aggregated artificial neural network (AANN) was used to investigate the simultaneous effects of layer thickness, delay time between spreading each layer, and print orientation of porous structures on the compressive strength and porosity of scaffolds. Two optimization methods were applied to obtain the optimal 3D parameter settings for printing tiny porous structures as a real BTE problem. First, particle swarm optimization algorithm was implemented to obtain the optimum topology of the AANN. Then, Pareto front optimization was used to determine the optimal setting parameters for the fabrication of the scaffolds with required compressive strength and porosity. The results indicate the acceptable potential of the evolutionary strategies for the controlling and optimization of the 3DP process as a complicated engineering problem.     

Two-axis flexure hinges with axially-collocated and symmetric notches

The paper introduces a new class of two-axis flexure hinges with axially-collocated and symmetric notches as an alternative to the existing flexure designs with serially-disposed notches. A generic formulation is developed in terms of the geometric curves defining the two notches which includes assessing the capacity of rotation, precision of rotation, sensitivity to parasitic effects, stress values, motion efficiency and shearing effects by means of compliance factors. Closed-form compliance equations are derived for a two-axis flexure hinge that is defined by two non-identical parabolic profiles. The analytical model predictions are confirmed by finite element data. A numerical comparison is made of the parabolic flexure with a constant rectangular cross-section flexure hinge in terms of several performance criteria.     

Design of high-bandwidth high-precision flexure-based nanopositioning modules

This paper presents the design of a single degree-of-freedom high-bandwidth high-precision nanopositioning module for high-throughput nanomanufacturing applications. Compared with widely used lumped-compliance mechanisms (using notch-flexure hinges) and distributed-compliance mechanisms (using compliant flexure beams), this nanopositioning module adopts a hybrid compliant-notch-flexure-based structure. This flexure design decouples the performance requirements for the structural bandwidth and parasitic accuracy that are correlated in the lumped-compliance mechanisms and distributed-compliance mechanisms. The parallelogram hybrid compliant-notch-flexure-based structure enables simultaneous achievement of a higher structural bandwidth and a smaller parasitic motion. The behavior of the nanopositioning module is analyzed theoretically with respect to its design parameters and performance objectives. Finite element analysis is adapted to study the dynamic responses and parasitic displacement of the designed nanopositioning module. The results from the theoretical and FEA analysis demonstrate the effectiveness of the hybrid compliant-notch-flexure design over commonly used lumped-compliance mechanisms and distributed-compliance mechanisms, especially when a high structural bandwidth is required for high-throughput nanomanufacturing applications.     

Hybrid Taguchi-cuckoo search algorithm for optimization of a compliant focus positioning platform

A long positioning range and a high first natural frequency are the two most important quality responses of a compliant focus positioning platform (CFPP). This paper aims to develop a hybrid Taguchi-cuckoo search (HTCS) algorithm to optimize overall the quality responses, simultaneously. The CFPP is designed via using flexure hinges. The length, width, and thickness of flexure hinges are considered as design variables. The Taguchi’s L₁₆ orthogonal array is used to establish the experimental layout and the S/N ratios of each response are computed. The analysis of variance (ANOVA) is computed to investigate the effect of design parameters on the quality responses. Results of ANOVA are then utilized to limit the search space of design parameters that serves as initial population for the cuckoo search meta-heurist algorithm. The results showed that the HTCS algorithm is more effective than DE, GA, PSO, AEDE, and PSOGSA. The CFPP enables a long positioning range of 188.36 μm and a high frequency response of 284.06 Hz. The proposed HTCS approach can effectively optimize the multiple objectives for the CFPP and would be useful technique for related optimization problems.     

Optimal design of a micro-positioning Scott-Russell mechanism by Taguchi method

In this paper, main features in kinematics of a micro-positioning Scott-Russell (SR) mechanism associated with two flexure hinges are its displacement amplification and straight-line motion, which are widely needed in practical industries. Without increasing the radial displacement, the SR mechanism is optimally designed by Taguchi method to obtain a maximum amplification of a small displacement driven by a lead zirconate titanate (PZT) actuator. According to kinematic characteristics of the SR mechanism the control factors include the direction, radius, width and offset of flexure hinges. It is found that the directions and offsets of flexure hinges have obvious effects on the amplifying factor and linearity ratio. The software ANSYS is utilized to obtain the numerical simulations, which are compared with the experimental results for the SR mechanism with and without offset of flexible hinges. Finally, some conclusions about the effects of control factors on the performance of the SR mechanism are drawn.     

基于压电陶瓷驱动的腹腔手术微型机器人

本文简要介绍了一个基于压电陶瓷驱动的腹腔手术用微型机器人系统，重点叙述了 微型机器人关节驱动部件的结构设计方案及其实现，对所设计的柔性铰链进行了定量力学分 析，并通过实验证明采用柔性铰链来实现驱动位移的放大是确实可行的．     

On the influence of local and global stress constraint and filtering radius on the design of hinge-free compliant mechanisms

Distributed compliant mechanisms are components that use elastic strain to obtain a desired kinematic behavior. Compliant mechanisms obtained via topology optimization using the standard approach of minimizing/maximizing the output displacement with a spring at the output port, representing the stiffness of the external medium, usually contain one-node connected hinges. Those hinges are undesired since an ideal compliant mechanism should be a continuous part. This work compares the use of two strategies for stress constrained problems: local and global stress constraints, and analyses their influence in eliminating the one-node connected hinges. Also, the influence of spatial filtering in eliminating the hinges is studied. An Augmented Lagrangian formulation is used to couple the objective function and constraints, and the resulting optimization problem is solved by using an algorithm based on the classical optimality criteria approach. Two compliant mechanisms problems are studied by varying the stress limit and filtering radius. It is observed that a proper combination of filtering radius and stress limit can eliminate one-node connected hinges.     

Design process and simulation testing of a shape memory alloy actuated robotic microgripper

Microgrippers are commonly used for micromanipulation of micro-objects with dimensions from 1 to 100 µm and attain features of reliable accuracy, low cost, wide jaw aperture and variable applied force. This paper studies the design process, simulation, and testing of a microgripper which can manipulate and assemble a platinum resistance temperature probe, made from a 25 µm diameter platinum wire, a 20 mm diameter tinned copper wire, and a printed circuit board type connector. Various microgripper structures and actuator types were researched and reviewed to determine the most suitable design for the required micromanipulation task. Operation tests using SolidWorks and ANSYS software were conducted to test a parallelogram structure with flexible single-notch hinges. The best suited material was found to be Aluminium alloy 7075-T6 as it was capable of producing a large jaw tip displacement of 0.7 mm without exceeding its tensile yield strength limit. A shape memory alloy was chosen as a choice of actuator to close the microgripper jaws. To ensure a repeatably accurate datum point, the final microgripper consisted of a fixed arm and a flexible arm. An optimisation process using ANSYS studied the hinge thickness and radius dimensions of the microgripper which improved its deflection whilst reducing the experienced stress.

     

Manufacture of microfluidic chips using a gap-control method based on traditional 3D printing technique

The solution to the commercialization of polymer microfluidic chips lies in the development of a low-cost and concise method. We present in this paper a gap-control method for obtaining low cost microfluidic chips on PMMA (polymethyl methacrylate) sheets based on traditional 3D printing technique—fused deposition modeling. The influence of 3D printing parameters such as printing temperature, printing speed, wire flow rate and initial layer thickness on printing quality is studied by experiments. The effect of O₂ plasma parameters such as chamber power and treatment time on the adhesion strength between printed PLA (polylactic acid) structures and PMMA substrate is investigated. The dye filling tests demonstrate that there is no blocking or leakage over the entire microchannels. With this newly developed technology, low-cost and large scale microfluidic chips can be fabricated, which allows commercial manufacturing of microchannels over large areas.

     

用于10-6N~10-5N微力测量的柔性铰链机构设计

在基于静电场原理的微纳力值测量系统中,力值的传递与转化机构起着至关重要的作用。选择平行四边形柔性铰链机构作为其弹性元件,以实现10-6N量级的力值测量。分析了柔性铰链的数学模型,研究了其静态与动态刚度;根据系统要求确定了柔性铰链的目标刚度,并采用有限元方法对其进行优化设计和模态分析;分析了加工精度对铰链刚度的影响。将该铰链用于微力测量系统中,通过实验给出了刚度测试结果和力值测量结果,实验表明,该平行四边形柔性铰链满足微力测量系统对10-6N量级的力值测量要求。     

Design of flexure hinge mechanism for 10-6 N~10-5 N micro force measurement北大核心CSCD

In a micro-nano force measurement system based on the principle of static electric field, the mechanism used for force transmission and transformation plays a vital role. The parallelogram flexible hinge mechanism is used as elastic element, in order to realize the measurement of force on the scale of 10-6 N. The mathematical model of the flexible hinge is analyzed to study the static and dynamic stiffness. The theory stiffness is determined according to the system requirement. The finite element method is used for the optimization design and modal analysis. The influence to the hinge stiffness of the machining accuracy is analyzed. The stiffness test and force value measurement results are given by experiments. Results show that the parallelogram flexible hinge can be used in the force measurement system on the scale of 10-6 N. ©, 2014, The Editorial Office of Chinese Journal of Sensors and Actuators. All right reserved.     

On using flexure‐hinge five‐bar linkages to develop novel walking mechanisms and small‐scale grippers for microrobots

This paper presents the micromotion analysis of five‐bar linkages and demonstrates the approximate linearity of motion transmission of five‐bar mechanisms within a micromotion range. A novel walking mechanism used for a microrobot and a small‐scale gripper with a high transmission ratio are introduced, based on the flexure‐hinge five‐bar mechanism analysis. Results of numerical simulation show the validity of design and analysis on the introduced mechanisms and the feasibility of corresponding thoughts. The presented micromotion‐based robot mechanisms are devoid of friction and fitting errors, and particularly suitable for microrobot applications. © 2004 Wiley Periodicals, Inc.     

Laser power based surface characteristics models for 3-D printing process

Selective laser melting (SLM) is one of the important 3-D Printing processes that builds components of complex 3D shapes directly from the metal powder. It is widely used in manufacturing industries and is operated on significant amount of laser power drawn from the electric grid. The literature reveals that the properties such as surface roughness, waviness, tensile strength and dimensional accuracy of an SLM fabricated parts, depend on the laser power and can be improved by its appropriate adjustment. Determination of accurate values of laser power and the other inputs could lead to an improvement in energy efficiency and thus contributing to a clean and healthy environment. For determining the accurate value of laser power in achieving the required surface characteristics, the formulation of generalized mathematical models is an essential pre-requisite. In this context, an artificial intelligence approach of multi-gene genetic programming (MGGP) which develops the functional expressions between the process parameters automatically can be applied. The present work introduces an ensemble-based-MGGP approach to model the SLM process. Experiments on the SLM process with measurement of surface characteristics, namely surface roughness and waviness, based on the variations of laser power and other inputs are conducted, and the proposed ensemble-based-MGGP approach is applied. Statistical evaluation concludes that the performance of the proposed approach is better than that of the standardized MGGP approach. Sensitivity and parametric analysis conducted reveals the hidden relationships between surface characteristics and the laser power, which can be used to optimize the SLM process both economically and environmentally.     

Structural synthesis for a lower-mobility parallel kinematic machine with swivel hinges

In this paper, a novel parallel kinematic machine is proposed. Its active platform (main supporting spindle) is manufactured with swivel hinges, that is, we substitute the spherical hinge with a swivel hinge. The active platform is also divided into several layers, which alters the characteristics of a single-layer-platform parallel machine. This paper applies a comprehensive structural approach based on position and orientation characteristics (POC). Each single open chain (SOC) is studied independently from the whole mechanism; we also analyse the POC of each kinematic pair. By the method of union, we obtain the POC matrix of the output motion of each link. Based on the verification of the 5-DOF (degree of freedom) parallel kinematic machine, we construct 3-DOF and 4-DOF parallel mechanisms with swivel hinges through the combination and union of different chains, and develop them into a series.     

A Two Degree of Freedom Gripper Actuated by SMA with Flexure Hinges

A gripper prototype was designed and built. It is made by a rigid structure articulated by compliant hinges. Its kinematics consists of both parallel and angular finger motion. The movements were designed to be independent from each other and auto‐adaptive as well. The motions were driven by Ni‐Ti shape memory alloy (SMA) wires. The recovery position is achieved by the elastic force exerted by the flexure hinges in the case of parallel motion and by an axial spring in the case of angular motion. Both the actuators and the hinges were experimentally characterized by suitable test rigs. The gripper prototype was tested and it showed to be able to reach the design performances. © 2003 Wiley Periodicals, Inc.