Customized evolutionary optimization procedure for generating minimum weight compliant mechanisms

In this article, a customized evolutionary optimization procedure is developed for generating minimum weight compliant mechanisms. A previously-suggested concept of multi-objectivization in which a helper objective is introduced in addition to the primary objective of the original single-objective optimization problem (SOOP) is used here. The helper objective is chosen in a way such that it is in conflict with the primary objective, thereby causing an evolutionary multi-objective optimization algorithm to maintain diversity in its population from one generation to another. The elitist non-dominated sorting genetic algorithm (NSGA-II) is customized with a domain-specific initialization strategy, a domain-specific crossover operator, and a domain-specific solution repairing strategy. To make the search process computationally tractable, the proposed methodology is made suitable for parallel computing. A local search methodology is applied on the evolved non-dominated solutions found by the above-mentioned modified NSGA-II to refine the solutions further. Two case studies for tracing curvilinear and straight-line paths are performed. Results demonstrate that solutions having smaller weight than the reference design solution obtained by SOOP are found by the proposed procedure. Interesting facts and observations brought out by the study are also narrated and conclusions of the study are made.     

多维加速度传感器的设计及优化

研制了一种基于单惯性质量块的一体化结构三维加速度传感器。依据传感器的工作原理,采用有限元工具对传感器静态和动态特性进行了分析,给出了弹性体的应变分布、固有频率及振型等,按各轴向灵敏度及其一致性和固有频率等目标对传感器结构尺寸进行了优化设计。有限元分析计算和实验结果表明,所研制的传感器在三个正交方向上都有较高的灵敏度,各加速度分量互干扰小。     

Development of 6-axis force/moment sensor for a humanoid robot's foot

The development of a 6-axis force/moment sensor considering adult weight for an intelligent foot of humanoid robot is described. To walk on uneven terrain safely, the foot should perceive the applied forces F_X, F_Y and F_Z and moments M_X, M_Y and M_Z to itself and control itself using the forces and moments. The applied forces and moments should be measured from a 6-axis force/moment sensor attached to the foot, which is composed of F_X, F_Y, F_Z, M_X, M_Y and M_Z sensors in a body. Each sensor has different rated loads because the applied forces and moments to foot in walking are different. Therefore one of the important tasks in developing the sensor is to design each sensor with the different rated loads and the same rated output. A 6-axis force/moment sensor for a humanoid robot's foot was developed using parallel plate-beams. The structure of the sensor was newly modelled, and the sensing elements (plate-beams) of the sensor were designed using theoretical analysis. Then, the 6-axis force/moment sensor was fabricated by attaching strain gauges on the sensing elements, and the characteristic test of the developed sensor was carried out. The rated outputs from the theoretical analysis agree well with that from the characteristic test.     

Topology optimization of compliant mechanisms using pairs of curves

The structural topology optimization approach can be used to generate compliant mechanisms for some desired input–output requirements. The success of the optimization depends on the structural geometry representation scheme used. In this paper, a novel representation scheme is proposed. The representation scheme is characterized by pairs of curves that are used to connect Input/Ouput (I/O) regions of the structure. Each pair of curves includes a normal curve and a fat curve. The areas bounded by the pair of curves define the material distribution between them. All I/O regions are connected to one another (either directly or indirectly) by pairs of curves in order to form one single connected load-bearing structure. A genetic algorithm for constrained and multiobjective optimization is then applied with the representation scheme of the structure in the form of a graph. Simulation results from a displacement inverter and a displacement redirector indicate that the presented representation scheme is appropriate.     

Topology optimization of compliant mechanisms using the homogenization method

A procedure to obtain a topology of an optimal structure considering flexibility is presented. The methodology is based on a mutual energy concept for formulation of flexibility and the homogenization method. A multi-objective optimization problem is formulated as an application of compliant mechanism design. Some examples of the design of compliant mechanisms for plane structures are presented. © 1998 John Wiley & Sons, Ltd.     

Hierarchical optimization for topology design of multi-material compliant mechanisms

Multi-material topology optimization enables potential design possibilities in the multiphysics and structural designing fields. In this article, a bi-level hierarchical optimization method is introduced to address the multi-material design of compliant mechanisms. The hierarchical optimization develops decomposition approaches allowing the original complex multi-material optimization problem to be reduced to set of low-order single-material optimization sub-problems. The solution of the complex multi-material problem is found as a vector of the single-material sub-problems solutions. All the local sub-problems are solved with the solid isotropic material with penalization method independently, and a stiffness spreading technique is worked out to coordinate components of the global solution of the original problem. Several numerical examples are presented to demonstrate the validity of this method.     

静重式力标准机独立加码过程仿真与优化分析

以100 k N的砝码加载过程为研究对象,从理论上提出一种消除逆程现象的方法。首先提出一种独立平滑加载方法,保证组合出的力值逐渐增大或者减小,使力值曲线平滑;并且建立数学模型,找到加载时进入平滑加载时间的有效区间;然后用Matlab进行仿真分析与优化。仿真优化结果表明:运用独立平滑加载从理论上可以消除逆程现象。     

单级柔顺正交位移放大机构非线性建模与优化

同时实现操作的灵活性与稳定性是精密工程领域的研究热点。单级柔顺正交位移放大机构可通过正交位移转换实现平行夹持,并通过位移放大提高操作的灵活性,但该机构的传统建模方法主要基于小变形假定并忽略剪切作用,导致模型精度较低。为此,对典型的单力输入单级柔顺正交位移放大机构进行精确的非线性建模与优化。考虑到剪切作用与几何非线性因素,对单级柔顺正交位移放大机构输出位移进行两步法半解析建模,以实现非线性结果的快速预测。第1步,基于能量法与欧拉-伯努利梁理论,建立该机构输出位移的线弹性解析模型,并结合小变形静力学有限元分析,拟合剪切非线性修正系数;第2步,结合几何非线性静力学有限元分析与数值拟合,建立该机构输出位移的几何非线性修正系数模型。为最大化输出位移并抑制几何非线性作用,提出机构平面尺寸和厚度综合优化策略,并利用ANSYS Workbench有限元仿真验证了机构输出位移非线性模型与优化结果的有效性。仿真结果显示,机构输出位移非线性模型的误差小于5%,且可依据不同优化策略显著增大输出位移或将几何非线性程度约束于指定范围内。研究表明利用所提出的方法对单级柔顺正交位移放大机构进行非线性建模与优化,可有效提高压电驱动柔顺微夹钳的位移输出性能与开环控制的精度和实时性,有利于实现稳定灵活的微操作。     

Topology optimization of hinge-free compliant mechanisms using level set methods

A new level set-based multi-objective optimization method is proposed for topological design of hinge-free compliant mechanisms. Firstly, the flexibility requirement of compliant mechanisms is formulated by using the mutual energy. Two types of mean compliance are developed to meet the stiffness requirement. Secondly, several objective functions are developed for designing hinge-free compliant mechanisms based on the weighting method in which a new scheme for determining weighting factors is used. Thirdly, several numerical examples are performed to demonstrate the validity of the proposed method. It is shown that the resulting compliant mechanism configurations contain only strip-like members which are suitable for generating distributed compliance and decreasing stress concentration.     

Transducing mechanical force by use of a diffraction grating sensor

A novel means of transducing mechanical force by using a polymeric-based diffractive grating sensor is presented. The diffraction gratings are successfully fabricated upon poly(dimethyl siloxane) polymer substrates by holographic interference and micromolding. A micromaterial tensile test incorporated into the surface diffraction grating experiment showed that a relationship between the load and the observed diffraction-pattern shift could be obtained. The results show an excellent correlation between the optical measurement and load, with a sensitivity of 0.05 N.     

Magnetic force driven nanogenerators as a noncontact energy harvester and sensor

Nanogenerator has been a very important energy harvesting technology through directly deforming piezoelectric material. Here, we report a new magnetic force driven contactless nanogenerator (CLNG), which avoids the direct contact between nanogenerator and mechanical movement source. The CLNG can harvest the mechanical movement energy in a noncontact mode to generate electricity. Their output voltage and current can be as large as 3.2 V and 50 nA, respectively, which is large enough to power up a liquid crystal display. We also demonstrate a means by which a magnetic sensor can be built.     

Analysis,design, and optimization of structures with integral compliant mechanisms for mid‐frequency response

A multi‐scale paradigm is proposed that utilizes periodic, small‐scale, integral compliant mechanisms within larger‐scale structures for the attenuation of vibro‐acoustic response. Amplification principles serve as the basis for the design of these mechanisms in achieving reduced energy transmission. The spectral finite element method is exploited for a force–velocity and energy flow analysis of the resultant truss‐like structures. A genetic algorithm is employed to optimize structure size for greatest effectiveness in the frequency range of interest. This study demonstrates that a significant decrease in structural vibration is achievable and suggests promising applications including the design of acoustic isolation panels for broadband vehicle noise reduction. Copyright © 2007 John Wiley & Sons, Ltd.     

Analysis,design and optimization of structures using force method and genetic algorithm

In the first part of this paper, the energy formulation of the force method is presented and analysis is performed using genetic algorithm. Two simple examples are provided to show the accuracy of the approach. In the second part, an efficient method is developed for designing structures with prescribed stress ratios for its members. The genetic algorithm performed very well and designs with specified stress ratios were achieved with a good convergence rate. A unit value of c_i for all the members of a structure corresponds to the well known fully stressed design. In the third part, minimum weight design is formulated by the additional conditions being imposed on the design process. Again, genetic algorithm showed to be a powerful means for optimization. Copyright © 2005 John Wiley & Sons, Ltd.     

Robust topology optimization of compliant mechanisms with uncertainties in output stiffness

This work addresses the topology optimization approach to design robust compliant mechanisms with respect to uncertainties in the output stiffness, when compared to the traditional deterministic approach. To this end, two formulations are proposed: probabilistic and nonprobabilistic. The probabilistic formulation minimizes a joint objective function of expected output displacement plus a measure of its standard deviations, for given statistical distribution of the output stiffness. The nonprobabilistic formulation is written as minimization of a joint function of the median of output displacements, plus the width of the intervals that contains the extreme values of the output displacements, for a given interval of output stiffness. The Monte Carlo simulation method is used to evaluate expected values and standard deviations of output displacements in the probabilistic formulation and to assess results obtained with the deterministic approach. It is shown that both formulations lead to designs where output displacements are less sensitive to variations of output stiffness when compared to the traditional deterministic approach. Furthermore, as an additional benefit, it is observed that large variations of output stiffness can hinder the appearance of one-node connected hinges, usually found in the deterministic design of compliant mechanisms.     

Techniques to suppress intermediate density in topology optimization of compliant mechanisms

Discrete topological problems are often relaxed with continuous design variables so that they can be solved using continuous mathematical programming. Such practice prevails because large-scale discrete 0–1 mathematical programming is not generally available. Although the relaxed problems become tractable, they may cause the appearance of intermediate density in the optimum topologies, especially those of structures and compliant mechanisms. Various penalty schemes have been proposed to suppress the intermediate density. Most of the past works assumed that the same penalty schemes could be effectively applied to both problems of stiffest structure design and compliant mechanism design. Differences in nature between the problems are generally neglected. This work distinguished the two problems, and observed that complaint mechanism (CM) problem does not suffer intermediate density as seriously as minimum compliance (MC) problem does. Besides allocating more material, explicit and implicit penalties were pursued to suppress intermediate density. To ensure mesh-independence and not to complicate the nonconvex objective function in CM problem, a new technique using a constraint of explicit penalty with variable bound is proposed to suppress intermediate density in topology optimization of compliant mechanisms. Together with a perimeter constraint, the new technique is also applied to MC problem. Received 13 March 2000     

错位熔接长周期光纤光栅横向压力传感器

阐述并实验证明了基于长周期光纤光栅和错位熔接结构的横向压力传感器,当施加于错位熔接点的横向压力改变时,干涉谱的相位保持不变,而纤芯模能量减少,包层模能量增加,导致消光比减小,以此通过消光比的变化实现对横向压力的测量.当横向压力从0⁰.98N增加时,传感器对压力的反应是单调且接近线性的.结果证明,该传感器具有消光比灵敏度高,成本低,结构简单的优点,在工业领域具有应用前景.     

新型自平衡液压式力标准机力值砝码系统

新建5MN液压式力标准机时,利用液压缸自平衡的新技术解决了初载荷的平衡问题,对该自平衡液压式力标准机力值砝码加卸载机构提出了新的设计,建立新的力值砝码组合方式,从而大大提高力标准机的工作效率。     

Self-temperature-testing of the quartz resonant force sensor

Temperature characteristics of a quartz resonant force sensor are important features, which should be seriously considered in the sensor's practical application. This paper analyzes the temperature characteristics of a quartz resonant force sensor and presents a self-temperature-testing method for the sensor by analyzing the different temperature characteristics when the quartz resonator vibrates in its fundamental mode and in its third overtone mode. A beat frequency results from the resonator's fundamental and third overtone frequencies. Experimental result show that the sensor's operating temperature can be measured by making use of this beat frequency rather than applying a temperature sensor     

压电式动态力传感器校准方法的研究

针对智能制造行业里压电式传感器的动态性能校准问题,介绍了针对传感器动态力参数的相关方法和脉冲力法校准装置,在装置上完成了试验验证和分析.介绍了两种常规的动态力校准方法,针对不同的校准方法建立了运动方程,做出了差异性分析.然后介绍了一种基于绝对法测量的压电式传感器脉冲力法校准装置,装置的结构包括基于刚体碰撞的脉冲力发生装...     

Characterization of microcantilever spring and force sensor using nanomanipulators

In this paper the authors present the development of a characterization process for microcantilever based spring and force sensor wherein fusion of real-time vision and force feedback is used. The process applies a very small force in micronewtons using MM3A nanomanipulators and senses the corresponding deflection using vision feedback, which produces direct characterization of microcantilever for evaluating its effective spring constant. The same process has been applied to find sensitivity of a microcantilever based force sensor. In the process force feedback values are viewed on a digital storage oscilloscope and once calibrated it is directly proportional to the applied force. By having known deflections (x) on images and known values of force (F) sensed by a force feedback sensor, the spring constant of microcantilever has been found as K = 8.75 μN/μm. Using the same procedure a microcantilever based force sensor has been characterized, the resulting sensitivity of force sensor has been found as 34.35 mV/μN.