基于压电陶瓷的柔性机器人主动抑振控制策略研究

柔性机器人因其轻质、高效、低能耗等优点已被广泛应用于航空航天,工业制造等诸多领域。然而,柔性机构易产生弯曲变形,引起系统振动而大大降低机器人的工作精度。为提高柔性机器人的工作性能,多种抑振策略得以研究与应用。提出了基于压电陶瓷（PZT）的柔性机器人振动主动抑制策略。其中,PZT传感器和PZT制动器分别被用来检测和抑制柔性臂的振动。本文构建了基于PZT材料的单自由度柔性机械臂的理论模型,并获得了传感电压与制动电压的传递函数。设计了一个可变控制方案的抑振器以抑制系统在不同频率下的振动。在COMSOL中进行仿真,获得了系统的抑振率。根据仿真结果显示,柔性臂在前三阶振动下,臂的末端位移分别得到了57.04%,57.76%与58.96%的抑制;系统的动能得到了57.95%,71.19%与87.81%的抑制。     

Difference thresholds for the perception of whole-body vertical vibration: dependence on the frequency and magnitude of vibration

When seeking to reduce vibration in transport it is useful to know how much reduction is needed for the improvement to be noticeable. This experimental study investigated whether relative difference thresholds for the perception of whole-body vertical vibration by seated persons depend on the frequency or magnitude of vibration. Relative difference thresholds for sinusoidal seat vibration were determined for 12 males at three vibration magnitudes and eight frequencies (2.5, 5, 10, 20, 40, 80, 160, 315 Hz) using the three-down-one-up method in conjunction with a two-interval-forced-choice procedure. The median relative difference thresholds were in the range 9.5% to 20.3%. There appeared to be a frequency-dependence at the lowest vibration magnitude, such that higher frequencies had higher difference thresholds. The relative difference thresholds depended on the vibration magnitude only at 2.5 and 315 Hz. The influence of both vibration frequency and vibration magnitude on the measured difference thresholds suggests that vision (at 2.5 Hz) and hearing (at 315 Hz) contributed to the perception of changes in vibration magnitude.     

Effects of hand vibration on reflex behaviors and pain perception – A pilot study

This research investigated the effects of hand vibration on the protective reflex responses and perception of the stimulus intensity. Electrical pulses were applied to the wrist to elicit the reflex responses. Changes of the reflex response were measured using the surface electromyographic activities from the hand flexor muscles, and were analyzed as a function of vibration frequency and initial level of grip force. Psychophysical experiment was also performed to assess the effects of hand vibration on perception of the electrical stimulus. The reflex responses were stronger during vibration, and were more visible at lower vibration frequencies and higher muscle contraction level. During vibration, a poor correlation was found between the reflex responses and stimulus perception.

Relevance to Industry

Results suggesting to adopt low level of grip exertion (light-weighted tool) and high vibration frequency to minimize the vibration-induced change of the protective reflex behaviors are useful to tool manufacturers and related workers.     

Rotation angle analyses of plate ultrasonic motor under dual-mode coupling drive

Speed improvements of plate ultrasonic motors could be achieved by choosing suitable excitation frequencies; however, the combination of these two frequencies is hard to be determined. Based on the linear superposition of vibrations at two independent mode frequencies, the rotation angles and amplitudes of modal vibrations are proposed to select the possible dual-frequency excitation combinations in this paper. Experimental prototype is a plate ultrasonic motor using single-phase asymmetric excitation, which can work under a single vibration or multiple vibration modes. The speed characteristics of prototype driven by dual-mode coupling are used to verify the coupling effects of dual-mode drive, in which each rotation angle of two modal vibrations is not close to vertical phase, and the two modal vibrations with larger amplitudes and closer rotation angles could improve the rotation speed of motor.     

Vibrations of skew plates immersed in water

Vibrations of skew plates immersed in water have been studied in the present work. Two skew prism fluid elements have been developed for the above study. As there is no information available on them, a few experiments have been conducted to measure the frequencies of vibration of these plates immersed in water. The results of both the theoretical and experimental investigations have been compared and found to be agreeing reasonably well. The general findings of these plates regarding their aspect ratios, thickness ratios and boundary conditions are discussed. In addition, the influence of skew angles on the vibration of skew plates have been investigated. It has been noticed that the effect of added mass is found to decrease with the increase of skew angle.     

超声悬浮及转子振动抑制理论与实验研究

超声悬浮技术可以实现悬浮和减摩功能,减少转子与静子之间的摩擦,而且由超声波产生的悬浮力可以不受悬浮物材料的影响.首先,根据流体动力学推导出超声波挤压膜的基本方程,对其进行理论推导并利用高阶差分方法进行仿真求解;针对气膜力与悬浮间隙、超声波振幅、气压、超声波频率因素的关系进行了分析,讨论了不同参数对超声悬浮性能的影响规律.然后,通过平面气膜力分解与合成推导出凹面气膜力,并研究了转速对其悬浮力的影响.将其施加在不平衡转子系统中,对转子系统的振动响应进行数值仿真,并对各个情况下的结果进行对比,探讨出不同参数下的振动抑制效果.最后,设计了超声悬浮-转子系统的实验台,通过实验测试不同参数下转子系统的振动响应,验证超声悬浮技术对于转子系统的振动抑制作用.     

漂浮式斜拉桥全局模态对CFRP索的敏感性研究

斜拉桥复杂动力学问题中的一个关键问题是局部模态频率与全局模态频率成倍数匹配关系时可能导致的斜拉索大幅振动.本文针对这个问题,基于传递矩阵法,研究CFRP索对斜拉桥全局模态频率的敏感性.将斜拉桥的桥面梁和桥塔分别视为多离散弹性支承欧拉伯努利梁,建立其动力学控制微分方程,基于传递矩阵法对其特征频率进行求解.以长沙某独塔斜拉桥作为算例,对结构主要构件:斜拉索、塔和桥面梁的刚度变化对全局模态频率变化的敏感性问题进行了分析.结果表明,桥面梁和桥塔全局模态频率对斜拉索刚度变化非常敏感,并且用CFRP索替换钢质拉索可能避开拉索局部模态与斜拉桥全局模态的倍频关系,从而控制斜拉索的大幅振动.     

Effect of applying ultrasonic vibration in thermal nanoimprint lithography

In our previous works we had shown that the use of ultrasonic vibration in micro hot embossing processes proved to be effective in improving the molding accuracy. We then decided to extend this technology of ultrasonic vibration to nanoimprint lithography also, and investigate its effect on nanoimprints experimentally. This task also required the use of a heater capable of sustaining three kinds of stresses, namely loading force, thermal stress, and ultrasonic vibration in the molding process. This work led to the development of an ultrasonic nanoimprint system with a built-in pyrolytic graphite/pyrolytic boron nitride all-in-one heater. The material chosen for nanoimprinting was polycarbonate with its glass transition temperature being 150°C. The research in the area showed that the timing point at which an impression of ultrasonic vibration begins is an important factor. When an ultrasonic vibration was impressed at an early stage in a molding process the height of the imprinted pattern seemed to increase where high amplitudes of the acoustical vibration were involved. Moreover, when the molding accuracies of line/space pattern with line widths of 500, 750 nm, and 1 μm were compared among themselves, the effect of assistance from ultrasonic vibration became quite noticeable in the case of small lines patterns; this was the case even where the amplitudes of the ultrasonic vibration were small. As for the application of ultrasonic vibration on nanoimprinting is concerned, it was found to greatly improve the molding accuracy of the process.     

Optimal design of an ultrasonic transducer

An ultrasonic transducer, consisting of two piezoelectric ceramic disks and two resonance rods, is optimized with respect to the shape of the two resonance rods in order to maximize the amplitude of the vibrating tip. The mathematical model is presented and a finite element model of the transducer is set up. Harmonic analysis (forced vibration) is used for calculation of resonance frequency, vibration mode, amplitude and phase. The resulting optimal shape is presented. The numerical analysis shows that the new design improves the amplitude 4.0 times. The improved transducer has been tested against the standard transducer and experiments show good agreement with theoretical results. A special design of the ultrasonic transducer for sonar applications has also been investigated. Applications of the improved ultrasonic transducer are more efficient transducers in high energy applications such as ultrasonic welding, drilling, disruption, cleaning, and sonar and underwater communication.     

Vibration characteristics of a rotating blade with localized damage including the effects of shear deformation and rotary inertia

The flexural vibration characteristics of a uniform rotating bar with localized zones of damage are studied by using a finite element analysis. The effects of shear deformation and rotary inertia have been taken into consideration. The influences of parameters such as the extent, position of damage and rotational speed on the frequencies of oscillation of the blade are discussed. It is observed that the presence of damage has a marked effect on the natural frequencies. A flaw in the beam near the tip of the blade has substantial effects on the frequencies as rotational speed increases. As the rotary inertia and shear deformation parameters increase, the frequencies increase for all damage parameters.     

Investigating the effects of vibration method on ultrasonic-assisted drilling of Al/SiCp metal matrix composites

Preciseness and finished surface quality are the significant factors of final products, especially in a number of drilling processes. Burr is usually considered a negative outcome in assembly procedures. One way to reduce or remove burr and improve surface roughness in metal cutting is to employ ultrasonic vibration in the drilling process. In this paper, the effects of ultrasonic vibration on burr size reduction, drilling force and surface roughness with two different vibration systems are investigated. To this end, two vibration structures were built, one to excite the workpiece (the workpiece vibration system) and the other to vibrate the tool (the tool vibration system). Besides, the effects of amplitude, feed rate, cutting speed, and SiC particle content on the drilling process of Al/SiCp metal matrix composites are studied. In all tests TiN-coated HSS drill tools with a diameter of 5 mm were utilized for drilling. Based on the attained results, it was demonstrated that suitable ultrasonic vibration reduced burr height, drilling force and surface roughness more so than conventional drilling. Meanwhile, in the workpiece vibration system, enhanced surface roughness and higher drilling force were obtained as compared to the tool vibration system.     

盘轴系统配合松动的振动特性研究

在采用过盈配合的大型盘轴转动机构中,由于转轴的输入转速太大,可能会导致盘与轴之间出现配合松动,影响系统振动特性.为了研究此系统的振动特性,建立了一个盘轴系统的动力学模型,模型的接触法向力、接触应力有两个线性阶段.通过仿真发现轴的输入转速大于某个转速后,盘轴系统的振动会在第一个线性阶段发散,到第二个线性阶段收敛,从而导致盘、轴的转速差,系统振动变成两个不同频率振动的叠加.第二线性阶段代表盘、轴出现间隙,表明此时出现松动.     

旋转圆环平面外振动的行波法研究

以高速球轴承保持架为应用对象,针对旋转薄壁圆环的平面外振动问题,开展弹性波传播的基本特性研究,分析平面外波动的色散方程、波数、截止频率、相速度以及位移耦合系数.基于行波动力学方法,根据波动正向传递的判据,将正负行波的波数进行分离.结合相位封闭原理和波传递矩阵,建立旋转圆环的频率特征方程.文中算例给出了旋转薄壁圆环平面外振动的固有频率,对其计算结果与文献结果作了比较,验证了计算方法的准确性.     

用于表达飞行姿态信息的组合式振动触觉编码

通过触觉传感帮助飞行员准确感知飞行姿态信息,减轻视听觉认知负担是信息的非视觉表达的一种大胆而有效途径.为此,设计了一种能提示飞机偏转方向和偏转角度的振动触觉显示方法.该方法充分考虑人对振动触觉刺激的敏感特性将姿态信息映射为一定振动节奏、振动位置和振动次序,从而形成组合式振动触觉编码,通过穿戴式振动触觉提示背心提示给人.与单控制参数的映射编码模式相比,该方法能显著提高振动表达的识别率,同时降低认知载荷.不同编码方法的感知识别实验表明,本方法在识别准确率,响应时间和训练时间上优于其他传统方法.     

Bedside safety rails: assessment of strength requirements and the appropriateness of current designs

This second paper in a series of studies of the discomfort produced by multi-axis vibration is concerned with rotational seat vibration. The effects of level, frequency and direction of the roll, pitch and yaw vibration of a firm flat seat have been studied in two experiments. At octave centre frequencies in the range 1-31.5 Hz the first experiment determined the levels of roll, pitch and yaw seat vibration which caused discomfort equivalent to 0-5 and l.25m/s²r.m.s. 10 Hz vertical seat vibration. In the second experiment, comfort contours equivalent to 0.8 m/s² r.m.s. 10 Hz vertical seat vibration were determined from 18 males and 18 females at preferred third-octave centre frequencies from 1 to 31.5 Hz. In all cases the axis of rotation passed through the centre of the seat surface. There was no vibration of the feet and no backrest.

It was concluded that the shape of equivalent comfort contours need not normally depend on vibration, level. Both individual and group equivalent comfort contours are presented. Although there were significant correlations between subject size and subject relative discomfort it is not thought that these correlations have much practical application. In all three axes the median contours of vibration acceleration increase in proportion to vibration frequency. Sensitivity is greatest for roll vibration and least for yaw vibration of the seat.     

Vibration and comfort HI. Translational vibration of the feet and back

The effects on discomfort of the frequency and direction of the translational vibration of a footrest and flat firm backrest have been studied in two experiments. At frequencies in the range 2.5-63 Hz, the first experiment determined the levels of fore-and-aft, lateral and vertical vibration of the feet of seated subjects which caused them discomfort equivalent to that from 0.8 m/s² r.m.s. 10 Hz vertical vibration of a firm flat seat. The levels of fore-and-aft, lateral and vertical vibration at the back of a seat which were equivalent to 0.8 m/s² r.m.s. 10 Hz vertical seat vibration were determined in the second experiment. The vibration of the feet or back occurred without simultaneous vibration at the seat.

Individual and group equivalent comfort contours are presented. It is concluded that the data provide a useful initial indication of the relative contribution of foot and back vibration to discomfort. Equivalent comfort contours for foot vibration were similar for all three directions of vibration. The contours for vibration of the back show a high sensitivity to fore-and-aft vibration. The results obtained from two additional studies show that vibration from a backrest and other variations in seating conditions can influence subject comfort.     

Equivalent comfort contours for fore-and-aft,lateral, and vertical whole-body vibration in the frequency range 1.0 to 10 Hz

Abstract

Standards assume vibration discomfort depends on the frequency and direction of whole-body vibration, with the same weightings for frequency and direction at all magnitudes. This study determined equivalent comfort contours from 1.0 to 10?Hz in each of three directions (fore-and-aft, lateral, vertical) at magnitudes in the range 0.1 to 3.5?ms^?2?r.m.s. Twenty-four subjects sat on a rigid flat seat with and without a beanbag, altering the pressure distribution on the seat but not the transmission of vibration. The rate of growth of vibration discomfort with increasing magnitude of vibration differed between the directions of vibration and varied with the frequency of vibration. The frequency-dependence and direction-dependence of discomfort, therefore, depended on the magnitude of vibration. The beanbag did not affect the frequency-dependence or direction-dependence of vibration discomfort. It is concluded that different weightings for the frequency and direction of vibration are required for low and high magnitude vibration.

Practitioner summary: When evaluating whole-body vibration to predict vibration discomfort, the weightings appropriate to different frequencies and different directions of vibration should depend on the magnitude of vibration. This is overlooked in all current methods of evaluating the severity of whole-body vibration.     

Effects of gender differences on the subjective perceived intensity of steering wheel rotational vibration based on a multivariate regression model

The aims of this study were to determine equal sensation curves for hand–arm steering wheel rotational vibration and to investigate the effect of gender on the subjective perceived intensity of steering wheel hand–arm vibration. Psychophysical response tests of 40 participants (20 males and 20 females) were performed using a steering wheel rotational vibration simulator using the category-ratio Borg CR10 scale procedure for direct estimation of perceived intensity. The test stimuli were sinusoidal vibrations at 22 third octave band centre frequencies in the range from 3 to 400 Hz, with acceleration amplitudes in the range from 0.04 to 27 m/s² r.m.s. Multivariate regression procedures were applied to the experimentally acquired data in order to establish a regression model expressing the Borg CR10 perceived intensity values as a function of the two independent parameters of the frequency and amplitude of vibration. The equal sensation curves suggested a non-linear dependency of the subjective perceived intensity on both frequency and amplitude. Females were found to provide higher Borg CR10 perceived intensity values than males (p < 0.05), particularly at the higher intensity levels above approximately 1.0 m/s² r.m.s and at the higher frequencies above approximately 20 Hz.

Relevance to industry

For the manufacturers of steering systems and of other automobile components this study provides vibration perception curves and identifies the possible importance of gender towards the perception of vibration which arrives at the steering wheel.     

Equivalent comfort contours for vertical vibration of steering wheels: effect of vibration magnitude, grip force, and hand position

Vehicle drivers receive tactile feedback from steering-wheel vibration that depends on the frequency and magnitude of the vibration. From an experiment with 12 subjects, equivalent comfort contours were determined for vertical vibration of the hands at two positions with three grip forces. The perceived intensity of the vibration was determined using the method of magnitude estimation over a range of frequencies (4-250 Hz) and magnitudes (0.1-1.58 ms⁻² r.m.s.). Absolute thresholds for vibration perception were also determined for the two hand positions over the same frequency range. The shapes of the comfort contours were strongly dependent on vibration magnitude and also influenced by grip force, indicating that the appropriate frequency weighting depends on vibration magnitude and grip force. There was only a small effect of hand position. The findings are explained by characteristics of the Pacinian and non-Pacinian tactile channels in the glabrous skin of the hand.     

The effects of vibration-reducing gloves on finger vibration

Vibration-reducing (VR) gloves have been used to reduce the hand-transmitted vibration exposures from machines and powered hand tools but their effectiveness remains unclear, especially for finger protection. The objectives of this study are to determine whether VR gloves can attenuate the vibration transmitted to the fingers and to enhance the understanding of the mechanisms of how these gloves work. Seven adult male subjects participated in the experiment. The fixed factors evaluated include hand force (four levels), glove condition (gel-filled, air bladder, no gloves), and location of the finger vibration measurement. A 3-D laser vibrometer was used to measure the vibrations on the fingers with and without wearing a glove on a 3-D hand-arm vibration test system. This study finds that the effect of VR gloves on the finger vibration depends on not only the gloves but also their influence on the distribution of the finger contact stiffness and the grip effort. As a result, the gloves increase the vibration in the fingertip area but marginally reduce the vibration in the proximal area at some frequencies below 100 Hz. On average, the gloves reduce the vibration of the entire fingers by less than 3% at frequencies below 80 Hz but increase at frequencies from 80 to 400 Hz. At higher frequencies, the gel-filled glove is more effective at reducing the finger vibration than the air bladder-filled glove. The implications of these findings are discussed.