Design of compliant straight-line mechanisms using flexural joints

Straight-line compliant mechanisms are important building blocks to design a linear-motion stage, which is very useful in precision applications. However, only a few configurations of straight-line compliant mechanisms are applicable. To construct more kinds of them, an approach to design large-displacement straight-line flexural mechanisms with rotational flexural joints is proposed, which is based on a viewpoint that the straight-line motion is regarded as a compromise of rigid and compliant parasitic motion of a rotational flexural joint. An analytical design method based on the Taylor series expansion is proposed to quickly obtain an approximate solution. To illustrate and verify the proposed method, two kinds of flexural joints, cross-axis hinge and leaf-type isosceles-trapezoidal flexural（LITF） pivot are used to reconstruct straight-line flexural mechanisms. Their performances are obtained by analytic and FEA method respectively. The comparisons of the results show the accuracy of the approach. Both examples show that the proposed approach can convert a large-deflection flexural joint into approximate straight-line mechanism with a high linearity that is higher than 5 000 within 5 man displacement. This can lead to a new way to design, analyze or optimize straight-line flexure mechanisms.     

Effect of Degree-of-Symmetry on Kinetostatic Characteristics of Flexure Mechanisms:A Comparative Case Study

The current research of kinetostatic characteristics in flexure mechanisms mainly focus on the improvement of accuracy. To reduce or eliminate the parasitic motion is considered as an approach by using the common knowledge of symmetry. However, there is no study on designing the flexure mechanisms with symmetrical features as many as possible for better kinetostatic performance, when considering the resulting cost by the symmetry. In this paper, the concept of degree of symmetry(DoS) is proposed for the first time, which is committed to symmetry design in the phase of conceptual design. A class of flexure mechanisms with 0?DoS, 1?DoS, 2?DoS and 3?DoS are synthesized respectively based on the Freedom and Constraint Topology method. Their overall compliance matrices in an analytical form formulated within the framework of the screw theory are used to analyze and compare the effect of different number of DoS on the kinetostatic characteristics for flexure mechanisms. The finite element analysis(FEA) simulations are implemented to verify the analytical results. These results show that the higher the DoS is, the smaller the parasitic motion error will be. The flexure model with 3?DoS is optimized according to the overall compliance matrix and then tested by using the FEA simulation. The testing result shows that with the best combination parameters, the parasitic motion error for 3?DoS mechanism is almost eliminated. This research introduces a design principle which can alleviate the unwanted parasitic motion for better accuracy.     

Development of a Leg Mechanism for Soft Landing Based on Biological Motion

With jumping mechanisms,soft landing motion is important to protect loads and the mechanisms.This study proposes a leg mechanism for soft landing based on biological motion.Human jumping motion with a load suggests a unique motion for soft landing.The landing model consists of two periods.Jerk is minimized in the first period and force is minimized in the second period.In comparison with other landing models,this model is specialized for soft landing motion protecting an objective part.Given all mechanisms ...     

并联机构驱动奇异的分层递阶滑模控制方法

以提高奇异鲁棒稳定性、控制精确性和降低控制能耗为目标,研究了并联机构的驱动奇异运动控制。以3-RPR型并联机构为例,运用螺旋理论和多刚体动力学理论进行了运动学分析和动力学建模;分别采用基于分层递阶结构的滑模控制方法和基于伪逆的滑模控制方法设计了运动控制器,对工作空间内不同的典型奇异位置进行了镇定控制仿真。结果表明,这两种控制方法均可达到较高的控制精度和较快的响应速度,且前者控制输入量更小、能耗更低。     

平面连杆机构运动误差综合的研究（Ⅱ）─—典型尺寸曲柄摇杆机构的运动误差特性

提出了机构运动误差特性的评价指标，揭示了曲柄摇杆机构尺寸类型与其运动误差特性之间的内在联系，编制了相应的图谱，从而为考虑运动精度要求的机构尺寸类型的选定提供了依据和方法．     

Real-time imaging of DNA-streptavidin complex formation in solution using a high-speed atomic force microscope

The direct observation of individual molecules in action is required for a better understanding of the mechanisms of biological reactions. We used a high-speed atomic force microscope (AFM) in solution to visualize short DNA fragments in motion. The technique represents a new approach in analyzing molecular interactions, and it allowed us to observe real-time images of biotinylated DNA binding to/dissociating from streptavidin protein. Our results show that high-speed AFMs have the potential to reveal the mechanisms of molecular interactions, which cannot be determined by analyzing the average value of mass reactions.     

Design principle of high-precision flexure mechanisms based on parasitic-motion compensation

In design of flexure mechanism, diminishing the parasitic-motion is a key point to improve the accuracy. However, most of existing topics concentrate on improving the accuracy of linear-motion flexure mechanisms via compensating the parasitic error, but few research the multi-dimensional flexure mechanisms. A general design principle and method for high-precision flexure mechanisms based on the parasitic-motion compensation is presented, and the proposed method can compensate the parasitic rotation in company with translation, or the parasitic translation in company with rotation, or both. The crucial step for the method is that the parasitic motion of a flexure mechanism is formulated and evaluated in terms of its compliance. The overall compliance matrix of a general flexure mechanism is formulated by using screw theory firstly, then the criteria for the parasitic motions is introduced by analyzing the characteristics of the resultant compliance matrix as well as with aid of the concept of instantaneous rotation center. Subsequently, a compliance-based compensation approach for reducing parasitic-motion is addressed as the most important part. The design principles and procedure are further discussed to help with improving the accuracy of flexure mechanisms, and case studies are provided to illustrate this method. Finally, an analytical verification is provided to demonstrate that the symmetry design philosophy widely used in flexure design can effectively improve accuracy in terms of the proposed method. The proposed compensation method can be well used to diminish the parasitic-motion of multi-dimensional flexure mechanisms.     

Modeling and analysis of motion of biological objects on the basis of a sequence of images obtained in studying the motion activity

A new approach to analyzing the data obtained by tracking biological objects in studying the motion activity is considered. The approach is based on a proposed mathematical model of motion of a biological object. The object behavior observed during the experiment can be described in the form of model parameters. A numerical experiment with model data is performed, which shows that the estimates predicted by the proposed method ensure a smaller root-mean-square deviation of the object state classification than other available methods.     

Approximating the times between closely-spaced impacts in mechanisms with clearances

In the analysis of the dynamics of mechanisms with clearance, problems of feasible motion between irregularly-spaced impacts and numerical solution arise. The solutions can be greatly advanced by proper choice of the clearance function, which turns out to be quadratic, e.g. text eqn (16). If this approach is pursued, a very simple integration scheme also results which affords a high degree of accuracy. The approach is illustrated by an example.     

Integrating mechanism synthesis and topological optimization technique for stiffness-oriented design of a three degrees-of-freedom flexure-based parallel mechanism

This paper introduces a new design approach to synthesize multiple degrees-of-freedom (DOF) flexure-based parallel mechanism (FPM). Termed as an integrated design approach, it is a systematic design methodology, which integrates both classical mechanism synthesis and modern topology optimization technique, to deliver an optimized multi-DOF FPM. This design approach is separated into two levels. At sub-chain level, a novel topology optimization technique, which uses the classical linkage mechanisms as DNA seeds, is used to synthesize the compliant joints or limbs. At configuration level, the optimal compliant joints are used to form the parallel limbs of the multi-DOF FPM and another stage of optimization was conducted to determine the optimal space distribution between these compliant joints so as to generate a multi-DOF FPM with optimized stiffness characteristic. In this paper, the design of a 3-DOF planar motion FPM was used to demonstrate the effectiveness and accuracy of this proposed design approach.     

混合驱动平面两自由度七杆机构最优运动规划

详细地分析了混合驱动平面两自由度七杆机构输入与输出运动之间的关系，并在此基础之上提出了闭链机构节点空间内运动规划的步骤与方法。基于改进遗传算法，提出了在闭链机构关节空间内处理具有运动学、动力学约束的最优运动规划问题的新策略。给出了算例并进行了仿真研究。     

Optimal Fixture Design Accounting for the Effect of Workpiece Dynamics

This paper presents a fixture layout and clamping force optimal synthesis approach that accounts for workpiece dynamics during machining. The dynamic model is based on the Newton– Euler equations of motion, with each fixture–workpiece contact modelled as an elastic half-space subjected to distributed nor-mal and tangential loads. The fixture design objective in this paper is to minimise the maximum positional error at the machining point during machining. An iterative fixture layout and clamping force optimisation algorithm that yields the "best" improvement in the objective function value is presented. Simulation results show that the proposed optimis-ation approach produces significant improvement in the work-piece location accuracy. Additionally, the method is found to be insensitive to the initial fixture layout and clamping forces.     

机械系统的运动传递与变换矩阵分析方法

提出一种机械系统运动变换的矩阵分析方法 ,建立了机构和机械系统运动类型变换、方向变换及运动变换的大小和特征的数学模型。定义了基本机构运动类型变换矩阵、运动方向变换矩阵 ,引入运动传递函数来表征运动的大小及特征 ,阐述了传递函数与运动方向变换矩阵的内在联系 ,讨论了其相应性质 ;综合运用运动类型与方向变换矩阵以及运动传递函数分析多个基本机构串联组成的机械系统所具有的类型、方向与运动特征和性质 ,建立了机械系统运动变换的统一数学模型 ,并给出计算实例。     

新的机构自由度计算公式——GOM公式的应用研究

总结了利用GOM公式计算机构自由度的具体步骤,列举了常用基础杆组的位移参数,介绍了杆组阶的确定方法;给出计算输出构件自由度及快速判断构件运动性质的方法;选取了几种典型的机构验证了所提出方法的正确性。结果表明,该新公式可以避开虚约束计算,不需要借助复杂的数学工具,便能快速、有效地计算包括混联机构在内的机构自由度,其正确性与通用性在一定程度上得到了验证。     

基于降质图像-光流场复原的智能轮椅测速

提出一种运动图像去模糊复原和基于仿射运动模型的光流场去抖动方法,以提高智能轮椅中光流里程计测速方法的精度。当轮椅线速度或角速度较大时,导致机载相机成像产生显著的运动模糊;且轮椅机器人的机械抖动也易产生光流场的偏差,进而影响速度估计的精度。针对于此,首先利用一种基于自适应模糊核的运动图像去模糊方法实现图像复原,以改善视频帧质量;其次,针对智能轮椅在行进中的机械抖动,利用随机抽样一致(RANSAC)排异后的光流场,在卡尔曼滤波框架下估计同名像点的仿射运动模型参数,进而实现光流补偿。实验结果表明所提方法能够提升基于光流场的智能轮椅视觉测速精度。     

Automated image mosaics by non‐automated light microscopes: the MicroMos software tool

Light widefield microscopes and digital imaging are the basis for most of the analyses performed in every biological laboratory. In particular, the microscope's user is typically interested in acquiring high‐detailed images for analysing observed cells and tissues, meanwhile being representative of a wide area to have reliable statistics. The microscopist has to choose between higher magnification factor and extension of the observed area, due to the finite size of the camera's field of view. To overcome the need of arrangement, mosaicing techniques have been developed in the past decades for increasing the camera's field of view by stitching together more images. Nevertheless, these approaches typically work in batch mode and rely on motorized microscopes. Or alternatively, the methods are conceived just to provide visually pleasant mosaics not suitable for quantitative analyses. This work presents a tool for building mosaics of images acquired with nonautomated light microscopes. The method proposed is based on visual information only and the mosaics are built by incrementally stitching couples of images, making the approach available also for online applications. Seams in the stitching regions as well as tonal inhomogeneities are corrected by compensating the vignetting effect. In the experiments performed, we tested different registration approaches, confirming that the translation model is not always the best, despite the fact that the motion of the sample holder of the microscope is apparently translational and typically considered as such. The method's implementation is freely distributed as an open source tool called MicroMos. Its usability makes building mosaics of microscope images at subpixel accuracy easier. Furthermore, optional parameters for building mosaics according to different strategies make MicroMos an easy and reliable tool to compare different registration approaches, warping models and tonal corrections.     

圆轨迹运动误差检测与信号处理

本文对精密仪器和机械中常见的运动形式——圆轨迹运动的误差建模、检测和识别进行了系统深入的研究。所提出的基于统计Ｂａｙｅｓ分类器的时域相关特征识别技术和基于距离测量分类器的频域谱线特征识别技术对实际圆轨迹运动误差的识别取得了满意的效果。该结果为精密仪器和机械圆轨迹运动精度的调试和误差控制提供了新的重要手段。     

Control and dynamic releasing method of a piezoelectric actuated microgripper

This paper proposes the control and dynamic releasing method of a symmetric microgripper with integrated position sensing. The microgripper adopted in this micromanipulation system is constructed by two L-shaped leverage mechanisms and the fingers of the microgripper is machined much thinner than the gripper body. A combined feedforward/feedback position controller is established to improve the motion accuracy of the microgripper in high frequency. The feedforward controller is established based on rate-dependent inverse Prandtl-Ishlinskii (P–I) hysteresis model. The inertial force generated in dynamic based releasing process is analyzed through MATLAB simulation. Open-loop experimental tests have been performed, and the results indicate the first natural frequency of the microgripper is 730 Hz. Then experiments in high frequency based on the developed combined controller are carried out and the results show the tracking error of a superimposed sinusoidal trajectory with the frequency of 100 Hz, 120 Hz and 130 Hz is 6.4%. Finally, the tiny objects releasing experiments are conducted where the combined controller is used to control the motion amplitude and frequency to achieve inertial force controllable to improve operation accuracy. And the results show that the dynamic releasing strategy is effective.     

A New Method to Determine Adhesion of Cantilever Beams Using Beam Height Experimental Data

A new method for calculating the apparent work of adhesion of microfabricated cantilever beams is presented and validated. This technique, based on popular beam mechanics, directly utilizes interferometrically produced deflection experimental data. The data are analyzed based on an energy minimization approach along the lines of a previous methodology. However, the new technique differs in that it does not rely on a priori knowledge of the shape of cantilever beams to evaluate work of adhesion. In order to validate the new method, both synthetic and empirical cantilever beam data were examined. The results show that apparent work of adhesion values calculated using this method agree well with values determined using a technique previously developed and widely accepted.     

Unsteady numerical analysis of the liquid-solid two-phase flow around a step using Eulerian-Lagrangian and the filter-based RANS method

The present study adopts the filter-based RANS (k-ε) method to analyze unsteady liquid-solid two-phase flow around a step in a rectangle channel. Numerical simulation was carried out in three dimensions using Eulerian-Lagrangian approach, in which the continuous phase is treated by Eulerian method and the motions of the dispersed phases are solved by Lagrangian method. The filter-based unsteady RANS (k-ε) model was implemented via user-defined functions in ANSYS Fluent 14.0. The flow field measurement by PIV experiment and the pressure fluctuation downstream the step were carried out for validation. Based on the comparison between the numerical and experimental data, results show that the pressure and velocity distributions were successfully reproduced. Compared with the standard k-ε model, the filter-based model can improve the prediction accuracy for wake flow and particle motion downstream the step. Furthermore, the numerical simulation reveals that the vorticity described by Q-criterion, promotes the particle motion at the wake area. However, the significant discrepancy of the particle distribution in the wake indicates the importance of turbulence modeling method for liquid-solid two-phase flow simulation.