【作者】 张增猛；

【导师】 周华；

【作者基本信息】 浙江大学 ， 机械电子工程， 2009， 博士

【摘要】 纯水液压比例技术是绿色水压传动的重要发展方向,而水辅成型技术则以高效高质和低成本等显著优势,成为塑料注射成型领域的研究热点。但是,现阶段的纯水液压比例技术由于元件成本高及技术本身不成熟,无法进入一般工业应用。水辅成型受到装备发展水平低的限制,在工艺研究和产业化方面遇到了困难。以水为媒介,将水辅成型与纯水液压比例技术有机结合,是提高水辅成型装备技术水平和拓展纯水液压传动应用研究的新思路。水辅成型充模流动水注射压力控制是影响成型效果的重要因素,也是纯水液压比例技术面向水辅成型系统应用研究的核心问题。然而,低成本纯水液压比例控制阀存在严重的非线性,不满足水注射压力控制的性能要求;水辅成型技术也未从装备角度开展研究,以解决工艺改进、系统控制、节能等方面的问题。因此,本文拟解决以下两个关键问题:第一,改善低成本纯水液压比例压力控制阀的控制性能;第二,建立适应水辅成型工作特征和负载特性的纯水液压系统,提出压力控制策略。在以上两个方面研究的基础上,针对水辅成型效果开展试验研究。本文根据纯水比例压力控制阀的静态特性分析,提出一种新的控制方法,即单边加入脉冲的前馈迟滞补偿,解决了阀死区和滞环大的非线性问题。针对水辅成型间歇循环工作特征和充模流动负载特性,提出了一种蓄能器压力的增压缸压差控制回路,采用纯水比例压力控制阀调节背压,使纯水液压系统的功率运行与水辅成型负载匹配,解决了节能和蓄能器压力调节的问题。建立了水辅成型充模流动的数学模型和负载线性模型,并根据纯水液压比例压力控制系统的仿真分析,提出了基于系统模型的蓄能器压力反馈校正的控制策略,消除了系统的微分环节。在国内外未研究的大截面型腔成型中,试验分析了压力控制和几何特征对成型效果的影响,为水辅成型纯水液压系统装备及其产业应用提供了技术支撑。论文主要结构如下:第一章,介绍了纯水液压比例技术和水辅成型技术的研究现状,提出了本课题需解决的关键问题,论述了本文的研究目的、意义和主要研究内容。第二章,建立了纯水比例压力控制阀的数学模型和分段线性迟滞模型,分析了影响阀静态特性的主要因素,提出了单边加入脉冲的前馈迟滞补偿方法,大大减小了阀的死区和滞环。第三章,建立了水辅成型充模流动的数学模型,通过流场仿真,分析了主要工艺控制参数对水辅成型制件残余壁厚和负载压力的影响,建立了水辅成型负载线性模型。第四章,针对水辅成型间歇、循环和压力流量变化范围大的工作特征,提出了蓄能器压力的增压缸压差控制回路,并设计和搭建了水辅成型纯水液压系统。建立了压力控制系统的数学模型,提出了基于系统模型的蓄能器压力反馈校正和带积分补偿的负载压力闭环控制策略。第五章,分析了不同水针流阻下系统输出压力的控制特性,试验研究了大截面型腔成型中压力控制与几何特征对成型效果的影响,并提出了对模具局部改进的水注射新方法。第六章,对本文所作研究工作进行总结,给出主要的研究结论,指出论文的创新点,并对未来的研究工作进行展望。更多还原

【Abstract】 Water hydraulic proportional control technology is an important developing direction of ’green’ water hydraulics.As well,water-assisted injection molding(i.e.WAIM) has attracted much attention in the field of injection molding technology,due to the advantages such as high efficiency,high quality,low cost and so on.However,water hydraulic proportional control technology is high-cost and has high environmental requirments.It is the main reason that there is nearly no application in common industry.Also WAIM research and industrialization are very difficult because of the restriction of low-level equipment development.The organic combination of WAIM reaearch and water hydraulic proportional control technology is a great idea to develop the WAIM system and extend the applications of water hydraulics.The water pressure control for cavity-filling process of WAIM is the key influence factor of forming effect, and is the key problem in the application research of water hydraulic proportional control in WAIM.The low-cost water hydraulic proportional pressure control valve is developed,whereas, it doesn’t meet the requirements of the injection water pressure control due to the great nonlinearity and poor performance.Meanwhile,the research on WAIM is not promoted on equipment development to solve problems of process improvement,system control,saving energy etc.For these reasons,there are two key problems in this thesis.Firstly,the control performance of the low-cost water hydraulic proportional pressure control valve should be improved.Secondly,the water hydraulic system is required to fit the process and load characteristics and the new control strategy should be proposed to control the water injection pressure.Based on these two researches,the experimental study is carried on aiming at fine molding effects.In this thesis,an innovative control method is proposed to decrease the dead zone and hysteresis of the water hydraulic proportional valve based on the sectional linear hysteresis model of the valve.That is a feed-forward static hysteresis compensation strategy with one-side pulse modulation.A novel differential pressure control of pressure cylinder is proposed to regulate the accumulator pressure,aiming at matching the intertiment work cycle and load characteristic of WAIM.The water hydraulic pressure control valve is used to regulate the back pressure in one chamber of the pressure cylinder opposite to another chamber connected with accumulator.The linear WAIM load model is built through flow field simulation on WAIM cavity-filling process. And the model-based feedback of accumulator pressure is provided to eliminate the differentiation element of the pressure control system.At last,the influence of pressure control on WAIM forming effect and the WAIM applicability with various geometrical conditions are investigated through experiments.These contribute to industrialization of water hydraulic system for WAIM.The thesis is outlined as following.In chapter 1,the state of the art of water hydraulic proportional control and WAIM technology is introduced.Key problems of this thesis are analysed.Purpose,significance and main contents are outlined.In chapter 2,the sectional linear hysteresis model of the water hydraulic proportional pressure control valve is built.The main factors influencing the valve static characteristic are analysed. The large dead zone and hysteresis are reduced significantly by feed-forward static hysteresis compensation with one-side pulse modulation.In chapter 3,the model of cavity-filling process in WAIM is built based on the time dependent analysis,turbulence models,and viscoplastic constitutive equations etc.Main process control parameters and linear load model are investigated in simulation.In chapter 4,a novel water hydraulic system is developed based on the differential pressure control of pressure cylinder and accumulator.A linear model of pressure control system is built. Model-based feedback and closed-loop control of load pressure with integral compensation are proposed and investigated.In chapter 5,the influence of flow resistance on system pressure control and molding effects with different water pins are investigated.WAIM applicability with various geometrical conditions and the influence of pressure control on WAIM forming effects are investigated by experiments.A novel method on water injection is provided with partial mould modification. In chapter 6,all the research ontents are summarized,and the future research developments and outlooks are proposed.更多还原