频率自动跟踪超声波电源设计

针对超声波电源工作时负载状态改变,换能系统产生谐振漂移的问题,提出了一种基于STM32的频率自动跟踪超声波电源的设计。电源逆变电路采用带辅助网络的全桥结构,阻抗匹配电路选择了一种改进型的T型匹配网络,应用PWM移相调功技术控制电源的输出功率,通过数字鉴相技术得到电压电流的相位差作为电路谐振状态的反馈信号,结合STM32主控制器进行PI控制,调节PWM波的输出频率使电路始终工作于谐振状态,实现了谐振频率的自动跟踪。最后基于该设计方案,实际制作了一款应用于超声波清洗仪的电源,并通过实验验证了该电源具有输出功率稳定,负载适应性强,输出频率自动跟踪等特点。     

医用回旋加速器回旋频率与磁场的调谐

高频谐振腔在回旋加速器实际运行过程中受束流负载、重力和热损耗引起的腔体变形等因素的影响,其谐振频率会发生一定的偏移,导致高频工作频率会随着谐振腔的谐振频率而变化.为满足等时性加速的要求,当高频工作频率发生改变时磁场强度也应进行相应的变化,即励磁电流的大小需要相应改变,使得粒子回旋频率与高频谐振频率相匹配以克服滑相.首先通过有限元仿真软件建立静磁场模型模拟不同励磁电流下回旋加速器的平均磁场,然后理论分析磁场与谐振频率的关系,最后得到励磁电流在小区间变化时与谐振频率的关系;根据计算的不同谐振频率对应的最佳励磁电流,完成励磁电流的自动跟频.在保证最大碳膜束流的情况下,实验得到不同谐振频率对应的最佳励磁电流,使理论得以验证.根据其关系实现了励磁电流自动调节,克服了滑相,保证了法拉第束流的稳定输出.该方法使得励磁电流能够快速、准确地寻找并跟踪谐振腔频率,克服了频率偏移导致的滑相,完成束流的稳定输出.     

基于单片机的超声冲击装置频率跟踪控制和恒幅控制

对超声波冲击以提高焊接接头疲劳强度的装置进行了研究，研制出一台可用于实际冲击处理的样机。该样机以单片机为核心，采用自适应带通滤波器提取超声换能器工作的基波信号，在此基础上获得电流和电压的相位差，根据相位差用模糊控制方法来实现自动频率跟踪；通过电流控制执行机构的输出端振幅，使之恒定不变，对超声冲击处理的质量进行控制。该装置能够适应超声冲击这种负载变化十分剧烈的场合，并可实现准确的频率跟踪和保证冲击处理的质量及效率。     

斜槽式单激励纵扭超声变幅杆设计*

为实现在纵向单激励超声振动输入条件下获得纵扭谐振输出,提出一种基于声波传播理论为基础设计阶梯型变幅杆,并在其小端增加沿中心轴均布6斜槽的圆环传振杆的方案：首先数值计算进行理论设计,然后使用有限元进行分析修正,最后确定变幅杆尺寸。结果表明：理论设计谐振频率20kHz,仿真分析在19457Hz时变幅杆能够实现纵扭谐振;根据仿真结果制作变幅杆,阻抗测试结果谐振频率为19884Hz,与理论值、仿真值误差较小;在输入端加载幅值为5μm的纵向单激励超声振动,测试输出端截面圆周上任意一点,其切向和纵向振幅分别为12.7μm和8.5μm,表明变幅杆实现了纵扭谐振且振幅增强。     

基于最小电压法的超声换能器谐振频率自动跟踪*

首先分析了最大电流法跟踪超声换能器谐振频率的原理及应用范围。研究了基于由串联电感和并联电容匹配电路下,不同频率时换能器两端电压电流的变化规律。研究表明在串联电感和并联电容匹配电路下发生谐振时,换能器两端的电压最小而电流并非最大。由此形成了采用最小电压法跟踪谐振频率的自动跟踪策略,并给出了该方法的具体实施步骤。论文研究结果为换能器谐振频率的自动跟踪方法提供了新的选择。     

超声焊接全状态频率跟踪算法*

与超声塑料焊接相比，超声金属焊接负载重且变化剧烈，容易导致换能器出现无阻性点状态或者频率误跟踪。现有的频率跟踪方法往往只能在换能器有阻性点的状态下正常工作，在出现误跟踪时也无法自动复位。针对上述问题，本文基于梅森等效电路，推导出一种能够同时适配于谐振频率与反谐振频率，能够自行判断是否误跟踪频率跟踪算法。当换能器处于无阻性点状态时，算法将自动把跟踪目标变为相位差最小点，实现全状态频率跟踪。算法利用三个不同频率及其发波时换能器的电压电流相位进行计算，以此算出理想的频率跟踪步长和方向。最后通过MATLAB对算法进行仿真，验证算法在目标频率发生非线性变化时频率跟踪的效果。结果表明，新算法能够实现误跟踪的自复位和全状态频率跟踪，同时能在启动后10ms以内完成频率跟踪，跟踪精度达0.1hz。     

非线性工作状态压电换能器匹配技术

针对压电换能器在大功率下存在复杂非线性而导致匹配参数难以优化的问题,以大功率超声金属焊接为例,通过采集测试焊接过程换能器两端电压的幅值与频率,建立换能器反谐振电阻与驱动电压有效值、频率之间的数学模型;提出基于反谐振电阻模型的最优功率匹配方法,推导了匹配电感电容的计算公式。最后实验验证了数学模型的准确性,且当换能器输入功率在最优功率附近时,匹配网络电能传输效率最高。     

串联谐振充电电源分析及设计

 推导了串联谐振充电电源不同工作模式下的电流、电压计算公式，给出了计算不同周期电流、电压值的递推公式；应用递推公式说明了这种电源的脉动恒流充电特性；给出了负载电容不完全放电情况下电源参数的计算方法。在负载电容完全放电的情况下，电源的平均输出功率为最大输出功率的一半，在负载电容电压基本维持恒定的情况下，电源平均输出功率与最大输出功率相等；最后给出了一台为Tesla型加速器初级储能电容充电的谐振电源的设计实例，电源的实测结果和计算结果一致，在100Hz重复频率下运行稳定可靠。     

基于电流和相位差的超声换能器频率自动跟踪

为了提高超声换能器频率跟踪的稳定性,通过对最小电流法和相位差法的原理和应用范围进行分析,提出了基于最小电流和相位差法相结合的并联谐振频率跟踪策略,该策略主要思想是将最小电流法运用于换能器空载阶段,相位差法运用于带载阶段,并且带载时的起始驱动频率取为空载阶段跟踪到的并联谐振频率。由此对最小电流法和相位差法这两种跟踪方法进行取长补短。基于该跟踪策略对换能器在不同负载下进行了实验,结果表明该策略可以快速地跟踪到换能器的并联谐振频率,并且工作稳定。     

HT-7U等离子体位移快控电源设计

针对HT-7U装置等离子体位移快控电源大电流快速响应要求,提出了一种基于电流型变流器的快控电源(FCPS)设计新方案。该方案采用交-直-交拓扑结构,即网侧采用电流型PWP整流器设计。以获得稳定的直流电流及网侧单位功率因数正弦波电流控制;负载侧则采用电流型H桥逆变器设计以实现负载电流的快速跟踪控制。移相PWM控制策略在实现多组变流器并联运行的同时,提高了变流器的等效开关频率控制,从而改善了电流波形品质。模拟系统实验论证了方案的正确性。     

Grain fragmentation in ultrasonic-assisted TIG weld of pure aluminum

Under the action of acoustic waves during an ultrasonic-assisted tungsten inert gas (TIG) welding process, a grain of a TIG weld of aluminum alloy is refined by nucleation and grain fragmentation. Herein, effects of ultrasound on grain fragmentation in the TIG weld of aluminum alloy are investigated via systematic welding experiments of pure aluminum. First, experiments involving continuous and fixed-position welding are performed, which demonstrate that ultrasound can break the grain of the TIG weld of pure aluminum. The microstructural characteristics of an ultrasonic-assisted TIG weld fabricated by fixed-position welding are analyzed. The microstructure is found to transform from plane crystal, columnar crystal, and uniform equiaxed crystal into plane crystal, deformed columnar crystal, and nonuniform equiaxed crystal after application of ultrasound. Second, factors influencing ultrasonic grain fragmentation are investigated. The ultrasonic amplitude and welding current are found to have a considerable effect on grain fragmentation. The degree of fragmentation first increases and then decreases with an increase in ultrasonic amplitude, and it increases with an increase in welding current. Measurement results of the vibration of the weld pool show that the degree of grain fragmentation is related to the intensity of acoustic nonlinearity in the weld pool. The greater the intensity of acoustic nonlinearity, the greater is the degree of grain fragmentation. Finally, the mechanism of ultrasonic grain fragmentation in the TIG weld of pure aluminum is discussed. A finite element simulation is used to simulate the acoustic pressure and flow in the weld pool. The acoustic pressure in the weld pool exceeds the cavitation threshold, and cavitation bubbles are generated. The flow velocity in the weld pool does not change noticeably after application of ultrasound. It is concluded that the high-pressure conditions induced during the occurrence of cavitation, lead to grain fragmentation in a pure aluminum TIG weld during an ultrasonic-assisted TIG welding process.     

Information contained in the radiating ultrasound during ultrasonic welding

During ultrasonic welding, unnecessary ultrasound together with audible sound is radiated into the air. Audible sound is noisy and uncomfortable, and ultrasound may have bed effects on adjacent equipment. However, it is considered that these sounds potentially contain useful information such as welding state. This article reports the relationship between radiated ultrasound and the change of the welding state during ultrasonic welding. It is known that the welding state can be presumed from the change of the mechanical load impedance, which can be calculated from resonant frequency, motional voltage and the driving current of the vibrating system for the welder when a constant-velocity motional-feedback power oscillator is used. In this study, radiated ultrasound picked up with a microphone and an amplifier is recorded and analyzed with a personal computer. Analyzed results are compared with the change of the mechanical load impedance that is also calculated from the recorded data of the resonant frequency, motional voltage and the driving current of the vibrating system for the welding. Experiments were made on the ultrasonic welding of plastic rods. The relationship between the parameters of radiated ultrasound and the electrical parameters of the vibrating system were compared. The peak amplitude of the radiated ultrasound and the mechanical impedance versus time were very similar. It is shown in this study that radiated ultrasound contains lots of useful information.     

Analysis of a fibre laser welding case study, utilising a matrix flow chart

For fibre laser welding of an eccentric corner joint, the quality of the resulting weld cross section was studied with respect to the dependence on process parameters like lateral laser beam alignment, beam inclination, focal plane position or welding speed. The complex load situation of the support beamer was simplified to bending of one corner. Due to fatigue load, the weld properties causing the peak stress are essential, in particular the top and root shape of the weld cross section. For the parameters varied, the resulting shapes were categorized into different top and root classes, determined by certain key dimensions, considering also welding defects like undercuts. The shapes are boundary conditions for Finite Element Analysis of the joint under load for quantitative comparative analysis of the maximum stress. As two high strength steel grades were joined, the hardness transition across the weld was of interest, too. High speed imaging of the weld pool surface shape provided additional information on the relation between the parameter input and quality output. The different trends identified were discussed and guidelines were derived. As the systematic documentation of results is unsatisfactory in welding, a new method was developed and applied for the first time, called the Matrix Flow Chart. It enables an illustrative view on the resulting welding trends in a combined manner and is extendable by other researchers.     

超声手术刀声学系统设计和实验*

为兼顾阶梯型变幅杆的高放大系数以及曲线过渡变幅杆突变截面处的高疲劳强度,本文提出了一种最速曲线过渡段的超声刀换能器。首先,基于等效电路法,设计了夹心式压电换能器的基本结构。在此基础上,结合超声刀的工作条件和材料特性,对换能器基本结构进行精确设计;然后,利用FEM法和实验法获取了换能器纵振频率以及频率响应曲线,进一步证明了本文所设计换能器的有效性;最后,对所设计的换能器进行了一系列测试,结果表明：测定了无负载换能器谐振频率与输出端振幅,与设计目标、仿真结果相吻合;连接负载后凝血,切割效果良好。     

不同焊接位置对5A90铝锂合金激光焊接质量的影响(英)

针对铝锂合金激光焊接产生的成形不良和气孔缺陷,探究不同焊接位置对焊缝成形及气孔的影响,并对比分析不同焊接位置熔池受力状态、熔融金属流动和小孔动态行为,解释缺陷形成及其抑制机理。研究发现:不同焊接位置熔池受力状态和熔融金属流动决定焊缝成形。平焊时焊缝成形差、下榻严重;横焊时背面焊缝不连续,有飞溅;立向上焊时背面焊缝内凹严重;立向下焊可得到最优焊缝成形和最优的气孔缺陷。焊缝气孔受小孔动态行为影响,不同焊接位置气孔随热输入的变化规律一致,气孔先增后减,在仅熔池透状态下有气孔最大值。立上焊时小孔不稳定,焊缝气孔多且分布杂乱;立向下焊时小孔稳定性高,气孔最少,主要分布在焊缝中心线上。     

Theoretical and experimental research on a disk-type non-contact ultrasonic motor

We developed a disk-type non-contact ultrasonic motor based on B22 vibration mode. The rotors of SU-8 photoresist are fabricated by the UV-LIGA process to control their shapes and thicknesses. So the structures of them are optimized by the experiments. It is found that the revolution speed of disk-type non-contact ultrasonic motor not only depends on the vibration amplitude of the stator, but also the weight and construction of the rotors. The maximum revolution speed of the optimal rotor is 3569 rpm at the input voltage of 20 V and the driving frequency of 45.6 kHz. The exciting principle of traveling wave is presented with theoretical equations. The electric signals applied to the piezoelectric ceramic are designed by the principle. The natural frequency and corresponding vibration mode are calculated and analyzed using finite element method. It is shown that experimental results are in good agreement with simulation, which verifies the effectiveness of the finite element model. Moreover, the levitation distance between the stator and rotor is measured by a CCD laser displacement transducer.     

Ultrasonic welding of CF/PPS composites with integrated triangular energy directors: melting,flow and weld strength development

This paper presents a fully experimental study on melting, flow and weld strength development during ultrasonic welding of CF/PPS composites with integrated triangular energy directors. The main goal of this research was assessing whether the heating time to achieve maximum weld strength could be significantly reduced as compared to ultrasonic welding with flat energy directors. The main conclusion is that, in the specific case under study, the triangular energy directors did heat up, melt and collapse approximately two times faster than the time it took for the flat energy directors to melt and significantly flow. However the heating time needed to achieve maximum weld strength for the integrated triangular energy directors did not differ drastically from that for flat energy directors. This was caused by the fact that a fully welded overlap was not directly achieved right after the collapsing of the triangular energy directors. Instead a solidified resin-rich interface was created which needed to be re-melted as a whole in order to achieve a fully welded overlap and hence maximum weld strength.