Tribological property investigation on a novel pneumatic actuator with integrated piezo actuators

Pneumatic piston–cylinder actuators are commonly used in industry for a variety of automation and robotics applications. In order to suppress leakage, these actuators comprise seal rings which unfortunately introduce friction and affect the positioning accuracy and output force. This article investigates vibrations of the seal generated by integrated piezo actuators to reduce friction force. For this, two piezoelectric stacks are integrated in the cylinder and used to excite vibration modes. This concept was studied in a compact cylinder pneumatic actuator with a bore diameter of 5 mm and a stroke of 10 mm. Dry friction measurement shows a 52% reduction from the original friction force at a driving frequency of 18.29 kHz and vibration amplitude of 0.05 μm. In the wet friction experiments, the friction force can be reduced by 54% from the original wet friction with vibrations at amplitude of 0.04 μm.     

旋转型压电惯性冲击马达的工作特性

为了研究惯性冲击机构中的旋转运动，设计了一台可调节预压力的旋转型压电惯性冲击马达。分析了该马达的运动原理及过程，研究了驱动信号、结构参数、压电元件等对马达运动特性的影响及规律。实验结果表明，该马达的转动速度与驱动信号的频率、电压成正比，与主体和配重的比值（M/m）成反比，转动速度随压电元件充放电时间增加而减小。研究还显示，旋转型惯性冲击马达的机械特性和正反转特性不同于电磁马达，该马达的转动速度-转矩特性为一折线，马达的正向转动速度始终大于反向速度。当驱动信号频率为1 100 Hz、电压为50 V、充电时间为70 μs、M/m=8.9时，该马达的转动速度为1.75 °/s，最大转矩为0.13 N·m。结果表明，旋转型惯性冲击马达是一个多变量系统，其运动性能受多种因素的控制。     

Dynamic characteristics and dual control of a ball screw drive with integrated piezoelectric actuator

This paper describes the precision continuous path tracking control by using a dual-actuated single stage. First, fine-drive mechanism and the dynamic model of the entire drive system are described. In the simulation model, the dynamic characteristic of the dual-actuated stage is investigated to see whether it can provide precise motion by using dual control. Second, the fine motion controller is designed. Adjusting the control parameters, a positioning resolution of 20 nm and a bandwidth of 260 Hz were obtained. Third, the frequency responses of coarse and fine drives are experimentally investigated. After that, the dual controller is designed based on the investigated dynamics. Finally, whether coarse motion and fine motion could work complimentarily by the dual servo is examined in the experiments. By using the simultaneous dual controller, tracking errors were reduced sufficiently compared to the single coarse control.     

基于转矩优化的双模式混合驱动特性研究

介绍了双模式混合驱动系统的结构和工作模式,研究了双模式混合动力传动装置的转速转矩关系。对发动机转速恒定时的输出特性进行了研究,分析了电力相对分流功率特性。需合理匹配行星机构参数,以降低第1模式电力相对分流功率。建立了以最大输出转矩为目标函数的非线性约束优化模型,对双输入行星变速系统进行优化求解,得到了变速传动装置输出转速从0到最高转速变化时,发动机、电机A和电机B的转速、转矩和功率的变化规律。     

Three DOF parallel link mechanism utilizing smooth impact drive mechanism

For a wide range of purposes, a compact and smart positioning stage is in strong demand. Our final goal is to fabricate a positioning mechanism that possesses multi-degrees of freedom, a wide movable area, dexterity, rigidity, and high speed. To meet most of requirements, i.e., except that of a wide movable area, a parallel mechanism is superior to a serial link mechanism. However, a lack of smart actuators has previously resulted in a large and complicated construction of a parallel mechanism.A purpose of this paper is to propose a new parallel link that utilizes a smart actuator called smooth impact drive mechanism (SIDM), and to verify its advantage for a smart and compact positioning stage. The SIDM actuator is an interesting mechanism that achieves a long stroke with fine positioning resolution. This paper treats a three DOF stage containing three SIDM actuators and a two-dimensional positioning sensor. The first operation test was carried out, and it was confirmed that a position control was successful. The average deviation was 18.6 μm and the standard deviation was 9.31 μm. As another trial, a circle 3.0 mm in diameter was successfully drawn. These values were insufficient for the SIDM actuator that has potentially nanometer-level resolution. The rough positioning resolution seems to be due to inferior driving method and mechanical ricketiness of the joints. In the near future, high speed and accurate positioning control could be realized with overcoming these problems.     

Robust isogeometric topology optimization for piezoelectric actuators with uniform manufacturability

Piezoelectric actuators have received substantial attention among the industry and academia due to quick responses, such as high output force, high stiffness, high accuracy, and precision. However, the design of piezoelectric actuators always suffers from the emergence of several localized hinges with only one-node connection, which have difficulty satisfying manufacturing and machining requirements (from the over- or under-etching devices). The main purpose of the current paper is to propose a robust isogeometric topology optimization (RITO) method for the design of piezoelectric actuators, which can effectively remove the critical issue induced by one-node connected hinges and simultaneously maintain uniform manufacturability in the optimized topologies. In RITO, the isogeometric analysis replacing the conventional finite element method is applied to compute the unknown electro elastic fields in piezoelectric materials, which can improve numerical accuracy and then enhance iterative stability. The erode–dilate operator is introduced in topology representation to construct the eroded, intermediate, and dilated density distribution functions by non-uniform rational B-splines. Finally, the RITO formulation for the design of piezoelectric materials is developed, and several numerical examples are performed to test the effectiveness and efficiency of the proposed RITO method.     

A procedure for evaluating the positioning accuracy of reciprocating friction drive systems

The dynamic characteristics of stick-slip motion in reciprocating friction drive systems are investigated under dry contact using a 0.45% carbon steel pair. Based on this dynamic analysis, the stick-slip motion can be eliminated under certain experimental conditions depending upon driver speed, normal load and spring constant. The effects of normal load, driver speed, and spring constant on the positioning accuracy of the reciprocating friction drive system are examined under harmonic oscillation without stick-slip motion. Results show that at very low spring constants, the slip increases with increasing driver speed such that higher normal load has better positioning accuracy or smaller slip than does lower normal load. However, at high spring constants and high normal loads, there exhibits severe wear or peak at two limit positions on the sliding region. As a result, smaller normal loads have a better positioning accuracy than larger normal loads due to severe wear at high normal loads.     

Output feedback integral control of piezoelectric actuators considering hysteresis

In this paper, output feedback integral control of piezoelectric actuators is considered with respect to the hysteresis effect. The linear dynamics of the piezoelectric actuator is modeled as a linear state space system with an input nonlinearity that considers the hysteresis effect. A proof of the Lyapunov stability of the system with integral control is presented, and a method for deriving the upper bound for the regulating gain is shown. A simple example is used to illustrate the approach, and then the approach is applied for tracking a step signal with an experimental single-axis piezoelectric actuator to verify that the system is stable.     

直线电动压缩机的活塞优化设计分析

为了满足直线电动压缩机的活塞高速化和轻量化要求,介绍了在PRO／MECHANIC环境下,对其活塞的应力和变形进行有限元分析,并对活塞进行优化设计,使其在满足强度和高速运转的情况下,质量达到最小,降低了惯性力,得到主要参数的最佳值,满足设计要求。     

Tribological behavior of reciprocating friction drive system under lubricated contact

The dynamic friction and wear behaviors are investigated in reciprocating friction drive system using a 0.45% carbon steel pair. The effects of various operating parameters on the traction force, stick and slip time, and friction modes are examined under the lubricated contacts. Moreover, the critical operating conditions in classifying three friction modes are also established. Results show that the fluid friction induced by the shearing of lubricant dominates the variation of traction force and produces the positive slope γ at the first period of slip in the traction force–relative sliding velocity curve. The γ value decreases at higher driver speed during stick-slip motion due to the thicker fluid film and shear thinning effect. The γ value increases due to the asperity interactions as the friction region is transferred from stick-slip to sticking with normal load from 196 to 980 N. Furthermore, it is also found that the static friction force is independent of stick time for the tangential loading rate ranged from 1.12 to 16.8 s⁻¹. The transition region produces the severest wear under the different driver speeds, but the wear is insensitive to the friction regions and the severe wear only occurs at higher normal load due to the action of Hertzian contact.     

Vibration control of smart hull structure with optimally placed piezoelectric composite actuators

Active vibration control to suppress structural vibration of the smart hull structure was investigated based on optimized actuator configurations. Advanced anisotropic piezoelectric composite actuator, Macro-Fiber Composite (MFC), was used for the vibration control. Governing equations of motion of the smart hull structure including MFC actuators were obtained using the Donnell-Mushtari shell theory and Lagrange's equation. The Rayleigh-Ritz method was used to obtain the dynamic characteristics of the smart hull structure. Experimental modal tests were conducted to verify the proposed mathematical model. In order to achieve high control performance, optimal locations and directions of the MFC actuators were determined by genetic algorithm. Optimal control algorithm was then synthesized to suppress structural vibration of the proposed smart hull structure and experimentally implemented to the system. Active vibration control performances were evaluated under various modes excitations. Vibration tests revealed that optimal configurations of MFC actuators improved the control performance of the smart hull structure in case of the limited number of actuators available.     

基于神经网络的车辆主减速器混合遗传算法优化设计

车辆驱动桥的组成包括主减速器、差速器和半轴,其中汽车主减速器的结构和尺寸极大的影响着汽车的动力学性能和经济性,因此采用优化设计方法来设计汽车主减速器是非常重要的。在满足主减速器接触强度、弯曲强度和边界约束的条件下,建立了优化设计数学模型。由于传统的优化方法存在着求解过程复杂和寻优过程容易陷入局部最优解的问题,故通过神经网络方法拟合待求系数,应用遗传算法工具箱调用混合遗传算法寻求最优解,使求解过程得到简化,确保可靠地获得全局最优解。     

Modeling of hysteresis in piezoelectric actuators using neural networks

For the application of neural networks to the approximation of hysteresis which is characterized of multi-valued mapping and non-smooth nonlinearities, a novel modeling technique based on a transformation of one-to-one mapping is proposed in this paper. In this method, a special hysteretic operator is introduced to describe the change tendency of the hysteresis with regard to its input. Then an expanded input space is constructed for hysteresis with the introduction of such hysteretic operator, on which the multi-valued hysteresis is decomposed into a one-to-one mapping. Thus, neural networks model for hysteresis is derived, avoiding the calculation of the gradient of hysteresis. Subsequently, for approximation of rate-dependent hysteresis in piezoelectric actuators which is caused by the dynamic voltage excitations, a hybrid model, i.e. the dynamic extension of the proposed neural hysteresis submodel is developed. In the model, a linear dynamic block is introduced in series with the proposed neural model to allow for rate-dependent dynamics of the piezoelectric actuator simultaneously. Also the corresponding optimization algorithm by use of the modified Levenberg–Marquarqt (MLM) method is given. Finally, the experimental validation results of applying both the proposed neural hysteresis model and hybrid model to a piezoelectric actuator are presented.     

新型压电旋转驱动器的设计与试验研究

为简化压电旋转驱动器的结构,提高能量使用效率,设计和研制一种新型压电旋转驱动器。驱动器采用压电双晶片作为原动件,经运动转换机构将其弯曲变形转化为扭转运动,再通过双离合器的耦合传动将扭转运动转化为旋转运动。使用有限元仿真分析方法和试验对驱动器的物理性能进行深入的研究,测得驱动器的关键参数。针对该驱动器的有限元仿真分析和试验研究表明,压电旋转驱动器的转速与驱动信号的频率、电压近似呈线性关系,驱动器具有一定的承载能力。对试验结果与有限元仿真分析结果进行误差分析,找出产生误差的原因,为驱动器的进一步优化设计提供了参考。研究证明了该压电旋转驱动器设计方法的可行性,使用该方法可以制作出结构简单,体积小,适合在微驱动领域中应用的压电旋转驱动器。     

Precise adjustment method using stroke impulse and friction

The present paper deals with an effective and alternative adjustment method for precise alignments of components of precision engineering and optics—the so-called method of stepped transfer of momentum bases on measured stroke impulses, which act onto a pre-stressed object and effect stepwise movements. The strokes are generated and applied to the components in several directions by special electromechanical hammers by means of a PC software and a measurement device. The automatic operation is finished if the target position of the object is attained. Achieved adjustment accuracies for the fixed components may be in the sub-micron range. The paper discusses theory and experiment of motion behavior of pushed components under the influence of applied momentum, pre-stressing and frictional forces. Additionally, it describes the wide application range of this adjustment method on the basis of developed prototypes.     

A laboratory simulation for stick-slip phenomena on the hydraulic cylinder of a construction machine

Stick-slip properties between steel and the glass fiber-reinforced nylon employed in the hydraulic cylinder of a construction machine were studied with a reciprocating tribometer as a laboratory simulator. A stick-slip evaluation method was established by introducing the running-in operation under certain operating conditions. Through studying the effect of sliding speed, the normal load and the viscosity, it was found that the sliding surfaces were operated in the mixed lubrication regime, where some friction modifiers were effective for elimination of stick-slip. Surface observation and surface analysis of the specimens after the tests indicated that stick-slip was mainly caused by an increase in the static friction coefficient due to transfer of iron oxide on to the seal surface from the steel surface. Subsequently, an attempt was made to correlate the results by the simulation test results for the hydraulic oil with those obtained by the hydraulic cylinder test.     

Hybrid controller of a linear piezoelectric walking stage relying on stack/shear piezoelectric actuators

This paper proposes a hybrid control strategy of a novel linear piezoelectric walking stage based on two sorts of piezoelectric actuators, which takes the load variation into account. The proposed stage consists of two parallel 4-bar lever amplification mechanisms with flexure hinges actuated by piezoelectric stacks to heighten the vertical distance (that is more tolerable to the assembly discrepancy), two compression springs (that is able to maintain a fixed linear position without powering), and two shear piezoelectric actuators (that can achieve longer and equivalent to walking motion) in a small form factor. The proposed stage has two operating modes, namely a coarse positioning mode with a more extensive travel range and a fine positioning mode with a nanometer-level resolution, to possess excellent performance for the linear piezoelectric walking stage of load variations. One multimodal switching controller and one feedforward-feedback controller conduct the coarse mode and fine mode, respectively. The optimal frequency for a specific load is obtained through a backpropagation neural network in the multimodal switching control. In the feedforward-feedback control, the inverse mathematical model based on the Bouc-Wen hysteresis model is used to mitigate the hysteresis effect in the feedforward part while the proportional–integral–derivative controller in the feedback part handles the external system disturbances. Experimental results show the proposed hybrid coarse/fine mode control strategy's effectiveness to satisfy an efficient and accurate positioning task.     

平面二次包络环面蜗杆传动多目标优化设计

平面二次包络环面蜗杆传动优化设计，通常以蜗轮齿固体积最小或以传动副性能最优为目标函数。为了兼顾该型传动副的性能和制造成本，以前述两种目标函数作为多目标优化设计的目标函数分量，建立了平面二次包络环面蜗杆传动多目标优化设计的数学模型，并用Matlab优化工具箱对模型进行了求解。     

谐波链传动的试验研究

以双支短幅内摆线的等矩曲线作为刚轮的齿廊曲线，设计制作了1台谐波链传动试验样机，通过试验验证了谐波链传动的运动可行性，采用分级加载的方式，证明了该传动装置的承载能力，并且分析了传动装置的速度波动情况。     

直接驱动式共轨系统可控针阀升程的驱动电路研究

针对柴油发动机喷油速率的控制问题,对喷油速率的控制方式进行了归纳总结,对直接驱动式共轨系统的特点和优势,以及直驱喷油器针阀的控制方式进行了分析,对于压电执行器的驱动电路以及充放电控制策略进行了分析,将可变电阻这一思路引入到电压反馈电路中,设计出了驱动电路的可变反馈模块,通过电控单元控制反馈电阻的选取,实现了在燃油喷射过程中对压电执行器驱动电压以及针阀升程的阶梯控制。对驱动电路进行了仿真优化设计,并利用压电执行器来对驱动电路进行了试验验证。研究结果表明,压电执行器完全充放电时间在120μs左右,喷油过程中驱动电压的变化可在100μs内实现,满足共轨系统对针阀的响应要求,所设计的驱动电路能够在燃油喷射过程中通过改变驱动电压来控制喷油速率。