Development of a high precision flexure-based microgripper

This paper presents the design and development of a high precision microgripper for micromanipulation. The design is based on a hybrid flexure-based compliant mechanism and a bias spring structure which render high fidelity and inherent mechanical advantages. Finite element analysis (FEA) was conducted to evaluate responses of the model under specified load and displacement to investigate optimum design of the model. The prototype of the proposed microgripper was fabricated using electro-discharge machining (EDM) process. An experimental study of the performance was carried out and the results are presented. The experimental results are also compared with the computational analysis results. The results show that a high level of displacement amplification and a maximum stroke of 100 μm can be achieved.     

双向作动大行程二自由度稳像机构

针对光学稳像系统的双向动态大行程的设计要求,本文设计了一种可伸缩双向作动的压电作动器,并基于此压电作动器设计了二自由度稳像机构。压电作动器由一个收缩式三角位移放大机构和一个伸张式三角位移放大机构组成。位移放大机构可为压电平台提供足够的行程,柔性铰链可使平台结构更加紧凑。接着,利用有限元分析软件ANSYS对平台结构进行静力学仿真,模拟了平台的位移和应力变化。最后对原理样机进行了实验分析,实验结果显示所设计压电平台在低电压和低频率下有足够大的行程和足够快的响应速度,作动器在120V电压下的输出位移在67μm左右,基本满足稳像系统的性能要求,故平台结构的设计方案是可行的。     

柔性二级差动式微位移放大机构优化设计

微位移放大机构常常用来扩大压电陶瓷致动器的行程范围。鉴于差动式微位移放大机构具有"小结构大倍数"的特点,设计了一种新型二级差动式杠杆微位移放大机构。应用矩阵表示法对其进行了运动静力学分析,在此基础之上,以柔性铰链的分布位置及其几何特征参数为优化变量,并以提高位移放大比和减小最大应力为目标函数建立一种双目标优化模型。机构经过优化设计后位移放大倍数高达48倍,并对其进行有限元仿真分析,计算结果为44倍,理论模型与有限元模型的误差小于10%。结果表明：提出的优化模型具有准确性和高效性,同样可适用于其他柔性铰链机构的优化设计。     

Analytical modeling, optimization and testing of a compound bridge-type compliant displacement amplifier

This paper investigates a flexure-based compound bridge-type (CBT) displacement amplifier for piezoelectric drives. In addition to the advantages of large amplification ratio and compact size, the CBT amplifier has a larger lateral stiffness and is more suitable for actuator isolation and protection than the ordinary bridge-type amplifier. An analytical model for amplification ratio calculation is established based on the Euler-Bernoulli beam theory because other simple theoretical approaches cannot predict the ratio properly. The reason why those approaches fail is discovered by resorting to the elastic model. The input stiffness and resonance frequency of the amplifier are also analytically modeled and verified by finite-element analysis (FEA). The derived models are utilized to optimize the amplifier structure through particle swarm optimization (PSO) to obtain a large resonance frequency subject to other performance constraints. The performances of the fabricated amplifier with optimized parameters are confirmed by both FEA simulation and experimental studies. Because an output displacement over 1 mm is achieved by the designed amplifier, it is employable to develop micro/nanopositioning stages with a cubic millimeter sized workspace.     

大行程高分辨率微定位机构的设计分析

压电驱动器的位移输出能力有限,因此通常借助于柔性机构对其位移量进行放大。对常用的柔性放大机构的性能进行了分析。提出一种柔性八杆放大机构,并对其进行有限元分析和理论计算。为了提高放大率,提出两级串连式机构。机构整体具有结构紧凑、放大效率较高的优点。     

柔性并联微夹取器的动力学分析及试验研究

针对一种具有毫米级操作空间和纳米级位移分辨率的、由直线超声电机驱动的柔性并联微夹持器,进行了动力学建模分析和实验研究。基于筷子夹取物体的操作原理,该微夹持器采用并联双层的结构形式。利用单位向量法,基于万向柔性铰链两端面始终平行的假设建立了微夹持器的运动学模型,表明了电机输入与操作末端输出之间的关系。采用ADAMS软件构建了微夹持器的刚柔耦合动力学仿真模型,由反向动力学仿真分析得到了微夹持器运行过程中几个重要的特征参数;由向前动力学仿真分析得到了操作末端,即探针尖端在给定输入函数下的位移、速度和加速度响应参数。对微夹持器的性能测试和夹取实验结果表明,该微夹持器的运行范围为2332μm×2109μm×20000μm,位移分辨率达到0.1μm,能够实现对微小物体的夹取操作。     

菱形压电微位移放大机构的设计

为提高叠层压电陶瓷作动行程,并使之具有往复对称作动的特性,提出一种基于三角放大原理的菱形压电微位移放大机构。该机构以叠层压电陶瓷作为驱动元件,利用三角位移放大原理,在放大叠层压电陶瓷位移输出的同时,实现在平衡位置两侧的双向主动输出。提出了相应的驱动方法,实现了对该机构输出方向和大小的控制。分析了机构的工作原理,通过解析计算得到该机构的理论放大倍数为2.9,与所建立有限元模型通过仿真计算得到放大倍数2.5相近。制作了试验样机并进行了试验验证,结果显示:该机构在驱动电压为200V时最大输出位移为(32±16)μm,对叠层压电陶瓷位移输出的放大比例为2.4倍,与理论计算相近;频率响应试验表明信号频率对位移输出影响较小。提出的设计方案实现了位移放大和位移双向主动输出这两个预期目标。     

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.     

垂直型多级位移放大机构设计与力学解析建模

针对压电位移放大机构在垂直方向较难实现大行程、高频带宽度的问题,结合两个复合菱形机构、两个杠杆机构以及一个普通菱形机构,提出了一种垂直型多级位移放大机构。基于能量守恒方法和弹性梁理论建立了位移放大比和输入/输出刚度解析模型,根据拉格朗日方程推导了固有频率解析模型。通过有限元法对解析模型进行了验证,所建立的位移放大比解析模型有较高的预测精度,可为大行程垂直型柔顺平台的优化设计提供参考。与文献中的位移放大机构性能对比结果表明,提出的垂直型位移放大机构具有更好的静动态平衡性能,其位移放大比可达43.29,同时保持一个较高的固有频率561.28 Hz。     

A novel driving principle by means of the parasitic motion of the microgripper and its preliminary application in the design of the linear actuator

This paper presents a novel driving principle by means of the parasitic motion of the microgripper. Actuators based on this principle can realize the large displacement range and high speed easily. Also the structure can be simple. A parasitic motion principle linear actuator mainly consisting of two piezoelectric stacks, two microgrippers and a mover was designed. Experimental results indicate that at a low driving frequency of 5 Hz, large velocity over 40 μm/s is obtained with the driving voltage of 100 V. Backward motion was observed and analyzed. Experimental results verify the feasibility of the new principle and it can be used to design new linear or rotary actuators.     

Design,modeling, and control of a monolithic compliant x-y-θ microstage using a double-rocker mechanism

This paper reports the design, modeling, and control of a novel three-degrees-of-freedom piezoelectric compliant microstage by introducing a new double-rocker mechanism. The double-rocker mechanism combines a first (leverage) amplifier and a second (rocker) amplifier for double-stage displacement amplification and parasitic motion reduction. An analytical model is established to calculate the deformation behavior of the microstage, and the model is verified using finite-element analysis (FEA). An improved Prandtl-Ishlinskii (PI) model is proposed to describe piezoelectric hysteresis characteristics by optimizing the threshold selection. Then, a composite control strategy is designed to achieve precision trajectory control. The control strategy consists of a hysteresis-based feedforward controller and a proportional-integral feedback controller. A prototype of the microstage is manufactured, and an experimental system is established. Several open-loop and closed-loop experiments are conducted, and the experimental results validate the effectiveness of the proposed microstage and the designed control strategy.     

毫米级微型机器人操作手的研制和操作特性

采用单晶片型压电悬臂梁制作了一种双悬臂梁结构的微型夹持器,用作毫米级微型机器人的微操作手.该微夹持器整体尺寸为15mm×2mm×2mm,重量为100mg.在分析该悬臂梁操作原理的基础上,选用PbNi_1/3Nb_2/3-PbZrO₃-PbTiO₃三元系压电陶瓷准同型相界的配方作为悬臂梁压电驱动材料,这种压电陶瓷具有高压电常数 (d₃₁) 和机电耦合系数 (K_p).进一步研究了压电微夹持器的操作特性.结果表明:50V电场下,其最大张口距离可以达到40μm,最大夹持力为25.7×10^-3N.     

A modified post-processing technique to design a compliant based microgripper with a plunger using topological optimization

The precision of microobject manipulation is predominantly based on the appropriate design of micromanipulation devices such as microgrippers. A compliant mechanism-based microgripper is an appropriate choice to achieve a highly precise and controlled motion. This research article proposes a refined technique to design a compliant-based microgripper with a plunger. The topological optimization technique has been adopted in this research work to develop the conceptual design of the mechanism. Flexure hinges are introduced in the topologically optimized design to overcome the senseless regions developed during the optimization process which is highly complicated to manufacture. Various flexure hinge contours such as rectangular, circular, and elliptical are introduced in the conceptual design domain, and their effects are investigated. Various parameters of flexure hinges are considered; the stress, the displacements, and the strain energy stored in the mechanism are studied through finite element analysis (FEA). In addition to FEA, experimental verification of the design was also performed. Both results are convincing about the structural performance of the microgripper design. In general, microdevices possess higher surface forces than volumetric forces; hence, this design is introduced with a plunger segment which is used to push the microobject for an active release during micromanipulation.     

Design and analysis of flexure-hinge parameter in microgripper

In the precision engineering field, a large number of applications require precise and microlevel manipulations, and microgrippers are an essential device to achieve precise manipulations. Highly precise movements are, in general, hard to achieve using conventional joints due to manufacturing error and backlash. In this paper, a new two-dimensional, compliant, monolithic piezo-actuated microgripper using flexure hinges is reported. The microgripper is designed, and a comparison study on stress and displacement is done by varying the hinge parameters such as the hinge radius, web thickness, position of flexure hinge, and radius of curvature of hinges. Kinematics of the microgripper is analyzed based on input/output displacement for all the above hinge design variations using FEM, and a kinematic model is arrived at based on the hinge location.     

Design and development of compliant mechanisms for electromagnetic force balance sensor

Compared with the lever-type amplifier, the rhombus-type amplifier has attracted more attention by virtue of large displacement amplification ratio, compact structure, and linear output displacement. In this paper, a novel electromagnetic force balance sensor (EFBS) based on the rhombus-type amplifier is presented to measure the mass with high precision. First, the structure and operating principle of the EFBS are described, and the requirements for the design and manufacture of the amplifier are put forward. Then, the analytical models of the two-stage rhombus-type amplifier are given out, and two guiding mechanisms are analyzed and modeled. Furthermore, the validity of the established model is verified by finite element analysis (FEA). Thanks to the theoretical guidance, an electromagnetic force balance sensor based on the two-stage rhombus-type amplifier and double parallelogram flexure mechanism is designed and tested. The experimental results demonstrate that the developed EFBS can measure the mass of the objects with high precision, and also verifies the correctness of the analytical model. This provides a new concept for the structural design of the EFBS.     

基于膜式液压放大的压电驱动器设计与试验

为解决叠堆式压电陶瓷输出位移微小的问题,结合液压放大的优点,提出了一种基于膜式液压放大的压电驱动器,并对关键部件--橡胶膜片进行有限元静力学、模态等分析。分析结果表明：橡胶膜片具有足够的安全强度和良好的工作频宽。在此基础上,研制其实物样机,搭建其测控平台,并进行了试验研究。开环试验结果表明：在0～100V电压控制下,所研制的压电驱动器输出位移范围为0～0.24mm,放大比约为5;闭环控制试验结果表明：采用分段PID的驱动器控制效果优于采用常规PID的控制效果,稳态误差约为±0.5μm。     

Analytical modeling and FEM Simulations of single-stage microleverage mechanism

Microleverage mechanisms have potentially wide applications in micro-electro-mechanical systems (MEMS) for transferring an input force/displacement to an output to achieve mechanical or geometrical advantages. Constrained by micro-fabrication technology, a microleverage mechanism is made of planar flexures, achieving mechanical transformation through elastic deformation. This kind of mechanism is referred to as a compliant mechanism. In this paper, the analysis and optimization of a single-stage microleverage mechanism is presented with a double-ended tuning fork as the output system in a resonant accelerometer to address the design issues. A very good agreement is obtained between the results of analytical modeling and those of FEM simulation with a SUGAR software package. Although the SUGAR data are more accurate, the analytical equations give clearer insights as to how to design a microleverage mechanism. While high axial spring constants and low rotational spring constants are desirable, the axial and rotational spring constants at pivot need to match those at the output system to achieve the maximum force amplification factor. This compliance-match concept is very important for the design of both single-stage and multiple-stage leverage mechanisms.     

An improved resonantly driven piezoelectric gas pump

Piezoelectric pumps have the potential to be used in a variety of applications, such as in air circulation and compression. However, piezoelectric membrane pumps do not have enough driving capacity, and the heat induced during the direct contact between the driving part and the gas medium cannot be dissipated smoothly. When the gas is blocked, the piezoelectric vibrator generates heat quickly, which may eventually lead to damage. Resonantly driven piezoelectric stack pumps have high performance but no price advantage. In this situation, a novel, resonantly driven piezoelectric gas pump with annular bimorph as the driver is presented. In the study, the working principle of the novel pump was analyzed, the vibration mechanics model was determined, and the displacement amplified theory was studied. The outcome indicates that the displacement amplification factor is related with the original displacement provided by the piezoelectric bimorph. In addition, the displacement amplification effect is related to the stiffness of the spring lamination, adjustment spring, and piezoelectric vibrator, as well as to the systematic damping factor and the driving frequency. The experimental prototypes of the proposed pump were designed, and the displacement amplification effect and gas output performance were measured. At 70 V of sinusoidal AC driving voltage, the improved pump amplified the piezoelectric vibrator displacement by 4.2 times, the maximum gas output flow rate reached 1685 ml/min, and the temperature of the bimorph remained normal after 2000 hours of operation when the gas medium was blocked.     

压电位移放大机构的力学解析模型及有限元分析

研究了压电位移放大机构的运动学和动力学建模问题。基于能量守恒原理和弹性梁弯曲理论推导了桥式位移放大机构的位移放大比等静力学解析模型;在此基础上,通过拉格朗日方程建立了桥式位移放大机构的固有频率解析模型。通过有限元计算验证和分析了提出的解析模型的可行性和优越性,并与国内外典型的位移放大比数学模型进行了比较。结果表明:由于本文提出的模型考虑了位移放大机构的拉伸和弯曲变形,并且摒弃了国内外普遍采用近似几何关系进行数学推导的思路,因此所建立的位移放大比解析模型精度更高;固有频率解析计算结果与有限元模态分析结果的相对误差约为5%。得到的结果显示:本文给出的建模方法以及位移放大比、固有频率等解析模型可为柔性机构的优化设计和研制提供依据和参考。     

压电陶瓷微夹钳迟滞环自适应逆控制研究

针对压电陶瓷的迟滞特性可使微夹钳难以获得良好的位移控制的问题，提出自适应逆控制策略。推导了压电悬臂位移特性的理论模型；采用自适应最小均方算法滤波器建立了压电悬臂的基于Backlash算子的迟滞环正逆模型，并以此为基础建立了微夹钳位移的自适应逆控制系统。样机测试和跟踪实验结果验证了所建立的理论模型和迟滞环模型的正确性，以及控制系统良好的自学习能力和控制效果。