A new design of piezoelectric driven compliant-based microgripper for micromanipulation

This paper describes the development of a microgripper mechanism capable of delivering high precision and fidelity manipulation of micro objects. The mechanism adopts a flexure-based concept on its joints to address the inherent nonlinearities associated with the application of conventional rigid hinges. A combination of two modeling techniques namely Pseudo Rigid Body Model (PRBM) and Finite Element Analysis (FEA) was implemented to expedite the prototyping procedure which leads to the establishment of high performance mechanism. A wire Electro Discharge Machining (EDM) technique was utilized to fabricate the monolithic structure of the gripper mechanism. Experimental studies were conducted on the model prototype to obtain various correlations governing the gripper performance as well as for model verification. The experimental results demonstrate a high level of integrity in comparison to the computational analysis. A high amplification characteristic and maximum stroke of 100 μm can be achieved.     

Computational parametric analysis and experimental investigations of a compact flexure-based microgripper

This paper presents a flexure-based piezoelectric actuated microgripper for high precision grasping/releasing tasks. The design of the microgripper consists of a three-stage amplification and transmission mechanism, and the parallel grasping technique. A bridge-type mechanism and two sequential lever-type mechanisms are symmetrically connected to amplify the output displacement of the embedded piezoelectric actuator. The parallelogram mechanisms assist in linearizing the output displacement of both jaws of the microgripper. The computational analysis is conducted to investigate the effect of the dimensional parameters on the characteristics of the microgripper. A computational parametric optimization methodology is established to achieve the required attributes of the microgripper. The design optimization resulted in a compact design, a high displacement amplification ratio, and a large output displacement of the microgripper. The experimental studies are conducted to investigate the key characteristics of the microgripper such as the displacement amplification ratio, the output displacement, tracking performance. Further, the parasitic motion, input-end and output-end motion resolution of the microgripper are identified. The experimental results indicate that the compact microgripper can achieve a high displacement amplification ratio and large output displacement with a high positioning accuracy.     

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.     

堆叠型压电执行器的动态蠕变补偿

在实验的基础上证实了压电执行器动态蠕变现象的存在。考虑到压电执行器的高频响特点和PID在高实时性要求场合的应用,构建了复合控制器来抑制动态蠕变。该复合控制器由具有Prandtl Ishlinskii类型的迟滞直接逆作为前馈控制器,由根据在线测试结果和实时性要求选择的增量式PI作为反馈控制器,其中增量式PI的参数由模糊逻辑控制器在线调节。通过实验验证了复合控制器抑制动态蠕变的有效性。结果表明,当同幅值的0.1 Hz正弦信号在一个周期内被离散化为20台阶,40台阶,80台阶时,相等电压台阶对应的蠕变过程和范围都是不同的。本文构建的复合控制器能够对不同台阶的动态和静态蠕变进行有效抑制,补偿后蠕变的均方根误差(RMSE)分别降低为补偿前的28.6%,31.0%和35.4%。     

具有反向PWM的阀门定位器控制方法及实现

压电式阀门定位器在行程范围内动态特性是非线性的,传统5步开关法在控制阀门过程中存在超调和PWM控制脉冲个数偏多的缺点.研究提出带反向PWM降速功能的五步开关法,在闭环控制过程中根据执行器运行速度的大小进行正向PWM控制和反向PWM控制的切换;在参数自整定过程中,针对不同位置寻找相应的最佳正向PWM占空比,并实现任意位置最佳正向PWM占空比的实时计算.研制了基于MSP430F5418A低功耗单片机的硬件和软件系统,实时实现参数自整定和控制算法.针对不同的气动调节阀进行了实验,取得较好的控制效果.     

Repair of a cracked Timoshenko beam subjected to a moving mass using piezoelectric patches

This paper presents an analytical method for the application of piezoelectric patches for the repair of cracked beams subjected to a moving mass. The beam equations of motion are obtained based on the Timoshenko beam theory by including the dynamic effect of a moving mass traveling along a vibrating path. The criterion used for the repair is altering the first natural frequency of the cracked beam towards that of the healthy beam using a piezoelectric patch. Conceptually, an external voltage is applied to actuate a piezoelectric patch bonded on the beam. This affects the closure of the crack so that the singularity induced by the crack tip will be decreased. The equations of motion are discretized by using the assumed modes method. The cracked beam is modeled as number of segments connected by two massless springs at the crack locations (one, extensional and the other, rotational). The relationships between any two spans can be obtained by considering the compatibility requirements on the crack section and on the ends of the piezoelectric patch. Using the analytical transfer matrix method, eigensolutions of the system can be calculated explicitly. Finally, numerical simulations are performed with respect to different conditions such as the moving load velocity. It is seen that when the piezoelectric patch is used, the maximum deflection of the cracked beam approaches maximum deflection of the healthy beam.     

Dynamic analysis of laminated composite plates with piezoelectric sensor/actuator patches using the FSDT mesh-free method

This paper investigates the active control of laminated composite plates with piezoelectric sensor/actuator patches using an efficient mesh-free method, i.e. the element-free Galerkin (EFG) method. The formulation of the problem is based on the first-order shear deformation plate theory (FSDT) and the principle of virtual displacements. A simple control algorithm coupling the direct and converse piezoelectric effect is used to control the dynamic response of the laminate plate with distributed sensor/actuator patches through a closed control loop. Several example problems are studied to show the influence of stacking sequence and position of sensor/actuator patches on the dynamic responses of the laminate plate. These simulations provide us with the best location of the sensor/actuator patches for active control of the laminate plate.     

基于动态模糊系统模型的压电陶瓷驱动器控制

针对压电陶瓷驱动器(PZT)的迟滞非线性对周期性超精密跟踪精度的影响,对基于Takagi-Sugeno(T-S)型模糊规则的动态模糊系统( DFS)前馈+PI控制方法进行了研究。介绍了DFS模型前提部分和结论部分的辨识方法; 结合直接逆模型控制和迭代学习控制的思想,提出了周期性轨迹跟踪的DFS前馈+PI控制方法。最后,针对20 Hz的三角波和正弦波期望轨迹进行了跟踪控制实验。实验结果表明：提出的控制方法对三角波和正弦波期望轨迹的最大跟踪误差分别为0.25%和0.27%,相对于PI控制,跟踪精度分别提高了52倍和64倍,而最大跟踪绝对误差分别降低到5.1 nm和5.5 nm。结果显示这种控制方法易于实现,周期性轨迹跟踪精度高。     

联合载荷作用下悬臂梁大变形分析的打靶法

利用微积分基本知识，这里导出了集中力和任意横向分布载荷作用下悬臂梁的挠曲线微分方程。基于两点边值问题的打靶法，分别计算了两种联合载荷作用下悬臂粱的大变形。所得微分方程不仅具有普遍性，而且本文的计算方法对类似问题的解决具有一定的借鉴意义。     

新型双向可控离合器的初步研究

联合动力装置现在已成为舰船动力的发展趋势,在这种装置中需要一种可以双向传递功率的离合器,即双向可控离合器.主要讨论了双向可控离合器在联合动力装置中的应用,根据离合器的工作特点提出两种初步方案,对两种方案的工作原理及结构特点进行了论述,并进行了比较分析,为联合动力装置中双向可控离合器的设计提供依据.     

Accuracy analysis of the amplitude estimation of a sine-wave by the energy-based method using the direct and indirect procedures

The energy-based method (EBM) can be used to estimate the amplitude of a sine-wave either directly from Discrete Fourier Transform (DFT) samples or indirectly. In this paper the accuracies achieved with both these approaches are compared when some of the most commonly used cosine class windows are adopted. The effect on the estimation accuracy of the algorithm error, the spectral interference from the image component, and wideband noise superimposed to the sine-wave signal are separately evaluated and compared. The statistical efficiencies of both procedures with respect to the unbiased single-tone Cramér-Rao lower bound are determined and compared. Moreover, the overall root mean square of the amplitude estimation error achieved when taking into account all the three contributions above is derived for both direct and indirect estimation procedures. The accuracy of the obtained expressions is verified by means of computer simulations. Besides, experimental data validate the theoretical results.     

遥控器用压电发电装置的供电特性

提出利用压电发电装置替代电池为遥控器提供实时的能量供应。针对遥控器的操作方法和负载特性,提出采用脉冲激励和按压激励压电振子的实施方案,通过试验的方法研究了压电振子在两种激励方式下对恒流负载的供电特性。结果表明,脉冲激励可获得更多的电能,适合于较大负载的工作场合。压电振子固有频率一定时,其有效的工作时间随电流负载增加而缩短;电流负载一定时,存在最佳的压电振子固有频率使其有效供电时间最长。利用尺寸为50x50x0.5mm的悬臂梁型压电振子为汽车遥控器供电,1次脉冲激励生成的电能可满足汽车遥控器信号发射的功率需求,信号传输距离达到15米以上。     

The systematic design and fabrication of a three-chopstick microgripper

In this study, we constructed a new type of gripper for micron-sized objects using piezoelectric multi-layer benders. This new gripper is composed of three chopsticks: two are designed to grip micro-objects, and the third is used to help grasp and release the objects. It is well known that a micro-object is much easier to grasp than to release. Electrostatic, van der Waals forces and surface tension between the chopsticks and object are believed to be the main causes of adhesion. We introduced a third auxiliary chopstick to overcome these surface effects and to reduce the electrostatic forces between the object and chopsticks. All three chopsticks were made of tungsten wires with ends sharpened by etching, which minimises the van der Waals effect. We constructed a three-chopstick gripper for micro-objects and tested its functionality by holding and releasing a 100-micron diameter object. The experiment showed that the third auxiliary chopstick functions effectively.     

基于动态线性化方法的自适应PD控制器的设计

传统PD控制对非线性系统和参数时变摄动的控制效果不理想,该文提出一种基于动态线性化方法的自适应PD控制器的设计方法。该方法通过输入输出数据对控制器中的比例增益实时调整,从而获得更强的鲁棒性,改善了动、静态性能。仿真结果表明,所提出的方法对系统的参数摄动具有较好的控制效果。     

Control of a permanent magnet synchronous motor with a fuzzy sliding-mode controller

This paper is concerned with the topics in the speed control of a permanent magnet synchronous motor (PMSM). First, the vector control scheme in the synchronously rotating reference frame is used to formulate the PMSM model as the system plant. Then, the modern control theory using a sliding mode with fuzzy controller is presented to design the corresponding closed-loop system and Matlab/Simulink software is used for computer simulation. The original PMSM is stable, sluggish with large overshoot deficiency. It can be shown that the proposed fuzzy sliding-mode controller not only can delete the overshoot problem and achieve very good tracking performance without zero steady-state errors, but can also obtain good robustness to system parameter uncertainty. This proposed fuzzy-sliding mode controller for PMSM can be applied to the positioning control of the robot arms to suppress unnecessary vibrations. For assembly lines, this proposed controller can be used to obtain fast tracking ability, less steady-state errors, and robustness for different velocity movements.     

具有三次非线性隔振的主被动控制系统动力响应的研究

运用非线性理论中的谐波平衡法,深入分析了底部具有三次非线性隔振且顶部装有 （主）被动调谐质量阻尼器的控制系统,就非线性对（主）被动控制系统的影响及相同非线 性情况下控制量对控制系统的影响进行了比较,为工程应用提供了重要的理论基础。     

Force control of a piezoelectric actuator based on a statistical system model and dynamic compensation

Piezoelectric actuators present a promising option if actuation of small-sized robot joints is considered. They develop forces of several newtons at velocities in the cm/s range while their dimensions and weight remain small as compared to electric motors. This work presents an approach for modelling a class of contemporary, non-resonant translatory piezoelectric actuators. The proposed modelling approach results in three motor models of increasing complexity independently of the low-level piezoelectric properties of the driving elements. The basic model establishes a static relation between motor velocity and drive frequency for a free-moving motor. The second model is a non-linear extension of the first model which introduces external load forces. The final model introduces time-dependent aspects by employing system identification techniques. The final model is used to develop a force compensation mechanism which restores linearity in the motor operation even in the loaded case. Based on the linearised model, standard control design techniques are applicable to design an explicit force controller. Limits on the performance of the controller are derived. The actual performance of the controller is evaluated both in simulations and experiments by pulling on tendons of different elasticity.     

动态频率测量的滞后误差分析及改进方法

采用常规方法测量动态频率时会产生滞后误差,该误差与被测信号的频率变化率以及测量结果的更新间隔时间成正比。为了降低滞后误差,对3种常规的频率测量方法进行改进研究。改进测周法,提出了周期跟踪法,当测量信号周期的定时器计时值超过上一个信号周期时,将定时器计时值作为信号周期并实时更新测量结果,从而缩短测量结果的更新间隔时间以降低滞后误差;改进多周期同步法,提出了分步移动式多周期同步法,在信号边沿中断程序中记录信号周期,并根据最近的若干个信号周期记录来计算信号频率,将测量结果的更新周期由多个信号周期缩短为单个信号周期,滞后误差最多可降低约2/3;改进计数法,提出了分步移动式计数法,采用计数器对信号数进行连续计数,将用于统计信号数的计时时间的1/n设置为定时器中断周期,在定时器中断程序中读取并记录计数器数值,根据最新记录的n个计数器数值来计算信号频率,将测量结果的更新间隔时间缩短为计数法的1/n,滞后误差最多可降低约2/3。     

起重机建模及载荷历程动态仿真

为在起重机结构的疲劳计算中采用应力幅法,着重探讨了基于多体动力学仿真软件ADAMS的桥式起重机虚拟样机模型的建立过程,并对桥式起重机的作业过程进行了动态仿真。     

电动助力转向系统建模及动力学仿真分析

通过汽车电动助力转向系统(EPS)的结构及其动力特性分析,建立其数学模型,针对其本身是一个比较复杂的非线性随动系统,采用模糊控制理论,设计一种自适应模糊PD控制系统,并进行仿真研究.仿真结果表明,基于模糊PD控制的电动助力转向系统比传统PD控制具有更好的助力特性和抗干扰能力.