Performance improvement of a drop-on-demand inkjet printhead using an optimization-based feedforward control method

The printing quality delivered by a drop-on-demand (DoD) inkjet printhead is limited due to the residual oscillations in the ink channel. The maximal jetting frequency of a DoD inkjet printhead can be increased by quickly damping the residual oscillations and by bringing in this way the ink channel to rest after jetting the ink drop. This paper proposes an optimization-based method to design the input actuation waveform for the piezo actuator in order to improve the damping of the residual oscillations. A discrete-time transfer function derived from the narrow-gap model is used to predict the response of the ink channel under the application of the piezo input. Simulation and experimental results are presented to show the applicability of the proposed method.     

FEM analysis of multilayered MEMS device under thermal and residual stress

It is essential to ensure reliability to produce a Micro-Electro Mechanical Systems(MEMS) on commercial scale. Reliability problem in inkjet printhead, one of MEMS, is also very important. To eject an ink drop, temperature of heater must be high so that ink contacting with surface reaches above 280° C on the instant. Its heater is embedded in the thin multi-layer in which several materials are deposited. MEMS processes are the main sources of residual stresses development. Residual stress is one of the factors reducing the reliability of MEMS devices. We measure residual stresses of single layers that consist of multilayer. FE analysis is performed using design of experiment. Transient analysis for heat transfer is performed to get a temperature distribution. And then static analysis is performed with the temperature distribution obtained by heat transfer analysis and the measured residual stresses to get a stress distribution in the structure. Although the residual stress is bigger than thermal stress, thermal stress is more influential on fatigue life.     

Effects of trapped air bubbles on frequency responses of the piezo-driven inkjet printheads and visualization of the bubbles using synchrotron X-ray

The reliability of drop formation is one of the key factors for the successful commercialization of inkjet printing applications. However, when the air bubble is entrapped from the nozzle exit, it leads to stop jetting of the droplets immediately. It has been known that the trapped air bubbles inside the chamber prevent a printhead from stable jetting. In this study the synchrotron X-ray has been used to visualize the air bubbles in the flow field inside of the printhead undergoing the standard jetting with the firing frequency of 1–20 kHz. An air pocket of bubble was formed repeatedly and reproduced well through the tested printheads at a certain jetting condition. To see the effects of the bubbles on the dynamic characteristics of the piezoelectric printheads, the piezoelectric velocity on the top of the pressure chamber was measured with a laser vibrometer. When the bubble was trapped at the nozzle exit orifice, the piezo velocity signals showed significantly different frequency peaks appearing in the spectrum and the high frequency components were identified with the frequency response measurements.     

Modeling and characterization of an industrial inkjet head for micro-patterning on printed circuit boards

A conceptual design using computational fluid dynamics (CFD) and micro-electro-mechanical systems (MEMS) fabrication has been performed to develop an industrial inkjet head for micro-patterning on printed circuit boards. The printhead has been fabricated with silicon and silicon on insulator (SOI) wafers by MEMS process and silicon to silicon bonding method. The measured displacement waveform from a piezoelectric actuator by laser doppler vibrometer (LDV) was used as input data for the three-dimensional flow solver to simulate the droplet formation. The mechanism of droplet ejection from piezoelectric-type inkjet heads was investigated by simulating two-phase flows of the air and metal inks. As a preliminary approach, liquid metal jetting phenomena are identified by simulating droplet ejection and droplet formation in a consequent manner. Parametric studies are followed by the design optimization process to deduce key factors to inkjet head performance: nozzle geometry, droplet size, ejecting speed, pulse amplitude, and ink viscosity. The present design tool, based on a two-phase flow solver and experimental measurements, has shown its promising applicability to various concept designs of industrial inkjet system for micro-patterning on electronic chips and boards.     

Fabricating chambers of inkjet printhead by bonding SU-8 nozzle plate with suitable crosslinked degree

Microsystem Technologies - The process of fabricating chambers is becoming increasingly important for inkjet printhead. However, the majority of present fabrication methods suffer from some...     

Effect of seed layer stress on the fabrication of monolithic MEMS microstructure

This paper reported the effect of seed layer stress on the fabrication of monolithic polymer-metal MEMS microstructure and what is a better material for the seed layer. The monolithic microstructure is gaining more and more attentions in MEMS application, especially in three-dimensional microstructure and inkjet printhead. The polymer–metal MEMS microstructure can be fabricated by combining the lithography and electroforming technologies. It is an integrated technology by batch process at low cost. The metal seed layer with large stress will lead to cracks and failure during the process integration. Several metal materials and thicknesses were studied to find a better candidate as the seed layer for the monolithic MEMS microstructure. The relationship between the monolithic MEMS structure and seed layer selection is also discussed. The lower residual stress of seed layer will result in a better surface condition for the followed integration process. The pure Ti metal and two-layer Ti/Au composite are the better seed layer materials in this study for the followed electroforming process of the monolithic polymer-metal MEMS microstructure.     

High-resolution long-array thermal ink jet printhead fabricated by anisotropic wet etching and deep Si RIE

This paper describes the fabrication and characterization of a thermal ink jet (TIJ) printhead suitable for high speed and high-quality printing. The printhead has been fabricated by dicing the bonded wafer, which consists of a bubble generating heater plate and a Si channel plate. The Si channel plate consists of an ink chamber and an ink inlet formed by KOH etching, and a nozzle formed by inductively couple plasma reactive ion etching (ICP RIE). The nozzle formed by RIE has squeezed structures, which contribute to high-energy efficiency of drop ejector and, therefore, successful ejection of small ink drop. The nozzle also has a dome-like structure called channel pit, which contributes to high jetting frequency and high-energy efficiency. These two wafers are directly bonded using electrostatic bonding of full-cured polyimide to Si. The adhesive-less bonding provided an ideal shaped small nozzle orifice. Use of the same material (Si substrate) in heater plate and channel plate enables the fabrication of high precision long printhead because no displacement and delamination occur, which are caused by the difference in thermal expansion coefficient between the plates. With these technologies, we have fabricated a 1" long printhead with 832 nozzles having 800 dots per inch (dpi) resolution and a 4 pl. ink drop volume.     

A thermal inkjet printhead with a monolithically fabricated nozzleplate and self-aligned ink feed hole

A monolithic thermal inkjet printhead has been developed and demonstrated to operate successfully by combining monolithic growing of a nozzle plate on the silicon substrate and electrochemical etching of silicon for an ink feed hole. For the monolithic fabrication, a multiexposure and single development (MESD) technique and Ni electroplating are used to form cavities, orifices, and the nozzle plate. Electrochemical etching, as a back-end process, is applied to form an ink feed hole through the substrate, which is accurately aligned with the frontside pattern without any backside mask. The etch rate is nearly proportional to the current density up to 50 μm/min. Experiments with a 50-μm-diameter nozzle show ink ejection up to the operating frequency of 11 kHz with an average ink dot diameter of about 110 μm for 0.3-A, 5-μs current pulses     

Fabrication of chamber for piezo inkjet printhead by SU-8 photolithography technology and bonding method

The chamber is an important part of the inkjet printhead. However, the present fabrication methods of chamber suffer from a low alignment resolution between nozzle plates and piezoelectric structure and residual SU-8 removing problems during chamber fabricating process. In this paper, a SU-8 chamber was fabricated by using ultraviolet (UV) photolithography and SU-8 thermal bonding method. By this method, the infilling problem of the chamber during thermal bonding process was solved, and low alignment resolution problem of conventional UV exposure system during assembly process was avoided. The thickness of the SU-8 nozzle plate was optimized, and the influence of bonding parameters on the deformation of chamber was analyzed. The simulation results show that the optimal thickness of the SU-8 nozzle plate is 40 μm and the optimal bonding parameters are bonding temperature of 50 °C, bonding pressure of 160 kPa and bonding time of 6 min. The tensile test results show the bonding strength of the SU-8 chamber is 2.1 MPa by using the optimized bonding parameter.     

Fluid dynamic behavior of dispensing small droplets through a thin liquid film

This paper presents a technology for dispensing droplets through thin liquid layers. The system consists of a free liquid film, which is suspended in a frame and positioned in front of a piezoelectric printhead. A droplet, generated by the printhead, merges with the film, but due to its momentum, passes through and forms a droplet that separates on the other side and continues its flight. The technology allows the dispensing, mixing and ejecting of picolitre liquid samples in a single step. This paper overviews the concept, potential applications, experiments, results and a numerical model. The experimental work includes studying the flight of ink droplets, which ejected from an inkjet print head, fly through a free ink film, suspended in a frame and positioned in front of the printhead. We experimentally observed that the minimum velocity required for the 80 pl droplets to fly through the 75 ± 24 μm thick ink film was of 6.6 m s^?1. We also present a numerical simulation of the passage of liquid droplets through a liquid film. The numerical results for different initial speeds of droplets and their shapes are taken into account. We observed that during the droplet–film interaction, the surface energy is partially converted to kinetic energy, and this, together with the impact time, helps the droplets penetrate the film. The model includes the Navier–Stokes equations with continuum-surface-tension force derived from the phase-field/Cahn–Hilliard equation. This system allows us to simulate the motion of a free surface in the presence of surface tension during merging, mixing and ejection of droplets. The influence of dispensing conditions was studied and it was found that the residual velocity of droplets after their passage through the thin liquid film well matches the measured velocity from the experiment.     

基于一维卷积循环神经网络的深度强化学习算法

针对现有深度强化学习算法在状态空间维度大的环境中难以收敛的问题,提出了在时间维度上提取特征的基于一维卷积循环网络的强化学习算法;首先在深度Q网络(DQN,deep Q network)的基础上构建一个深度强化学习系统;然后在深度循环Q网络(DRQN,deep recurrent Q network)的神经网络结构基础上加入了一层一维卷积层,用于在长短时记忆(LSTM,long short-term memory)层之前提取时间维度上的特征;最后在与时序相关的环境下对该新型强化学习算法进行训练和测试;实验结果表明这一改动可以提高智能体的决策水平,并使得深度强化学习算法在非图像输入的时序相关环境中有更好的表现。     

Performance characterization of drop-on-demand micro-dispensing system with multi-printheads

Due to the diversity of printhead activation mechanism, printhead design and its operational parameters, integrating heterogeneous printheads is usually preferred in multi-material micro-fabrication tasks. However, evaluating the performance of multi-printhead micro-dispensing system is seldom investigated. In this paper, the developed micro-dispensing system performance along X and Y axes is discussed based on the attached two printheads, i.e. solenoid actuating micro-valve and piezoelectric printhead. Comprehensive experiments are conducted to characterize droplet size and their deposition performance on the substrate. To explore the optimal printing parameters (e.g. pitch and printing speed), the characterization results are analyzed in terms of deposition accuracy and line straightness, printable conditions, and stability. It can be concluded that an optimal pitch is the key to achieve better line straightness for micro-valve printhead. For normal printing using piezoelectric printhead, the selection of printing speed is determined in terms of pitch. A lower speed is recommended for both to minimize the disturbance from printheads’ point-to-point motion. In addition, some other factors’ influence on printing accuracy such as vibrations, printhead synchronization, printing time are discussed. Our study on the relationship between printing parameters and dispensing performance will not only benefit the optimization of micro-dispensing performance, but also the development of theoretical models or empirical equations in the 3D micro-fabrication process.     

土工筋带变形测试传感器研发与试验研究

工程上,土工加筋带变形测试一直是个难题,主要是因为其应变较大且加筋带外层是相对较软的聚合物结构.利用纳米导电炭黑颗粒充填聚合物获得敏感材料,再通过印刷技术将其印刷在塑料薄片上,制作成传感元件.通过拉伸试验测试了四种不同底板传感元件的传感性能,试验结果表明,四种元件均具有拉伸敏感性,电阻值随拉伸应变的增大而增大,且满足模量匹配与较大应变要求.对比分析发现,PVC底板传感元件的综合性能最佳,适合作为土工筋带变形测试元件使用.另外,这种方法制作的传感元件可批量化生产,无需逐个标定,极大地提高了它的实用性.     

Reliability characterization of a soot particle sensor in terms of stress- and electromigration in thin-film platinum

In this work we present a systematic investigation of various failure mechanisms for thin-film platinum heater structures and interdigitated electrodes as components of a resistive type soot particle sensor. We study the role of stress-migration and electromigration and their interaction for the reliability of these sensors. The influence of a titanium adhesion layer and gases from the ambient atmosphere are also studied. Lifetime determination and optical and scanning electron microscopy are applied for samples which have experienced different load conditions to understand qualitatively and quantitatively the phenomena. The aim of this work is to enable time-to-failure prediction and thus provide guidelines for limiting temperature and current density in the actual sensor to ensure its stability over lifetime. We use dedicated, application-related test structures to ensure that the results are applicable to sensor lifetime estimations.     

虚拟技术在变压器冲击试验中的应用研究

针对如何有效及时地发现即将投入电网运行以及正在电网中运行的变压器所存在的绝缘缺陷,减少此类故障或事故的发生,避免变压器绝缘问题所导致的灾害,基于虚拟仪器技术平台设计了一种具有集成高压示波器、高速记录仪、脉冲峰值表等专用仪器仪表功能的标准变压器冲击试验测试系统,该系统装置具有强大的数值分析和记录功能。通过对所作的冲击试验研究结果分析,该试验装置能够及时发现变压器层间、匝间和主绝缘存在的绝缘缺陷,从而可以避免因变压器绝缘缺陷所带来的危害。     

A restructured artificial bee colony optimizer combining life-cycle,local search and crossover operations for droplet property prediction in printable electronics fabrication

For printable electronics fabrication, a major challenge is the print resolution and accuracy delivered by a drop-on-demand piezoelectric inkjet printhead. In order to meet the challenging requirements of printable electronics fabrication, this paper proposes a novel restructured artificial bee colony optimizer called HABC for optimal prediction of the droplet volume and velocity. The main idea of HABC is to develop an adaptive and cooperative scheme by combining life-cycle, Powell’s search and crossover-based social learning strategies for complex optimizations. HABC is a more biologically-realistic model that the reproduce and die dynamically throughout the foraging process and the population size varies as the algorithm runs. With the crossover operator, the information exchange ability of the bees can be enhanced in the early exploration phase while the Powell’s search enables the bees deeply exploit around the promising area, which provides an appropriate balance between exploration and exploitation. The proposed algorithm is benchmarked against other four state-of-the-art bio-inspired algorithms using both classical and CEC2005 test function suites. Then HABC is applied to predict the printing quality using nano-silver ink. Statistical analysis of all these tests highlights the significant performance improvement due to the beneficial combination and shows that the proposed HABC outperforms the reference algorithms.     

民居节能建筑外墙保温层最优厚度仿真

为提高建筑外墙保温层厚度计算结果的精度,提出基于LCCA(Life Cycle Cost Analysis)的民居节能建筑外墙保温层最优厚度计算方法。根据采暖度日数、建筑物围护结构的传热阻等值计算建筑外墙热损失。利用保温层投资与采暖燃料投资相加所得值,获取单位面积建筑外墙保温层的生命周期范围内总投资。采用反应系数法与z传递函数法分析并计算围护结构非稳态逐时热流。结合外墙热损失、保温层使用寿命内费用和墙体逐时热流分析结果,计算民居节能建筑外墙保温层最优厚度。实验发现,保温层存在一个最优厚度,可以使建筑的总费用降到最低;相同保温材料,最优保温层的厚度会随着现值因子增大不断增大,随着采暖度日数增大逐渐增大,随着非保温层热阻值增大不断减小;保温材料不同,最优保温层厚度的差异体现在随着现值因子、采暖度日数增大逐渐增大,随着外墙的非保温层热阻值增大逐渐减小;保温层最优厚度计算结果与实际值拟合度高。     

大型三维真彩色喷墨控制系统

针对三维喷绘机器人的作业需求,设计了一种基于FPGA的大型三维真彩色喷墨控制系统.系统以Virtex-Ⅱ Pro FPGA内嵌的PowerPC405硬核为中心,通过移植Xilkernel嵌入式操作系统和LwIP网络协议,搭建了一个多任务实时处理平台;并自主设计了满足喷头控制时序的IP核及相应驱动,硬件协加速单元在位置触发信号的节拍控制下执行喷墨过程.试验结果表明,系统灵活性较强,实时性较好,能够准确、高速地进行三维真彩色喷墨.     

电缆测试仪绝缘电阻测试单元的研制

现有的电缆故障检测系统是对复杂电缆网络短路、断路故障自动检测的系统,但不具备对电缆网络导线之间绝缘性进行测试的能力.本文研制了一个与原有电缆故障检测系统兼容的绝缘测试单元,阐述了绝缘电阻测量模块、通道选择模块、高压产生模块、EPLD译码模块等电路的设计实现过程,实现对电缆网络的绝缘测试.     

基于深度强化学习的燃料电池混合动力汽车能量管理策略研究

为提高燃料电池混合动力汽车的燃油经济性和燃料电池寿命,该文提出一种基于深度强化学习(Deep Reinforcement Learning,DRL)的能量管理策略.该策略首先在DRL奖励信号中加入寿命因子,通过降低燃料电池功率波动,起到延长燃料电池寿命的效果;其次,通过限制DRL的动作空间的方法,使燃料电池系统工作在高...