摘要
液体粘性传动(简称液粘传动)调速起动装置利用摩擦片间油膜的剪切作用来传递动力,从而实现机械设备的可控起动过程。在降低机械设备的制造及运行成本、延长使用寿命等方面具有明显的作用。本文以带式输送机为应用对象,对液粘传动调速起动及其控制技术开展研究工作。
在对液粘传动调速起动的工程背景、调速起动的意义、基本原理及其优越性进行论述的基础上,对国内外研究现状及液粘传动调速起动方面存在的问题进行了综合分析,提出了本文的主要研究内容。
对液粘传动调速起动机理进行了较深入的研究,由于调速起动过程是一个瞬态过程,起动过程中油膜厚度始终在动态地变化,存在油膜挤压效应。本文综合考虑了油膜挤压效应以及摩擦片表面粗糙度和油膜离心力的影响,建立了修正瞬态雷诺方程,同时建立了热能量方程和工作油粘温方程。通过有限元模型的数值计算,对调速起动过程中油膜厚度的变化、油膜传递扭矩、油膜承载力及油膜压力场和温度场进行了分析研究,得出了油膜挤压效应、摩擦片表面沟槽截面尺寸和布置方式、摩擦片表面粗糙度和工作油通过摩擦片后的温升对油膜承载力和传递扭矩的影响规律。
在对摩擦片组进行受力分析的基础上,建立了摩擦片组的动态平衡方程,同时建立了系统的流量平衡方程和负载的动态平衡方程,并对本文实验所采用的比例溢流阀的动态特性进行了实验研究,确立了其传递函数。根据调速起动的特点,分别推导出比例压力控制系统和比例流量控制系统的传递函数,并对其动态响应特性进行了分析比较,结果表明比例压力控制系统较适合于带式输送机的调速起动。
对PID控制及PID优化控制的调速起动特性进行了较深入的研究,对Harrision起动速度曲线进行了计算机仿真,结果表明两者均不能满足带式输送机调速起动的需求,输出速度相对于给定速度有一定的滞后,并且存在振荡现象。在此基础上提出了模糊PID串级控制,分析了其动态响应特性并对Harrision起动速度曲线进行了计算机仿真,结果表明输出速度能较好地跟踪给定速度且无振荡现象,是带式输送机调速起动较理想的控制方法。
为验证理论分析的正确性及控制策略的有效性,设计制作了液粘传动调速起动实验台,并分别采用PLC和单片机搭建实验平台,对PID优化控制和模糊PID串级控制进行了相应的实验研究。结果表明采用模糊PID串级控制不仅输出速度能较好地跟踪给定速度,且无明显的速度波动,证明了理论分析的正确性。同时通过实验研究讨论了工作油温度、负载大小及起动时间对调速起动的影响规律。
A hydro-viscous drive speed regulating start equipment transfers power by shearing force of oil film between friction discs, so as to realize the controllable startup process of mechanical equipment. It has great significance both in reducing manufacturing & operating cost and in prolonging servicing life of mechanical equipment. With belt conveyor as application object, the research work on hydro-viscous drive speed regulating start and control technology has been carried out.
This paper discusses the engineering background, significance, basic principle and superiority of hydro-viscous drive speed regulating start, analyzes domestic and abroad research status, points out current problems of hydro-viscous drive speed regulating start, and presents research contents of this thesis.
The mechanism of hydro-viscous drive speed regulating start is deeply studied. Since speed regulating start is a transient process and the oil film thins out gradually during the whole startup process, the effect of oil film squeezing cannot be neglected. With a comprehensive consideration of oil film squeezing effect, the effect of friction disc surface roughness and centrifugal force of the oil film, the modified transient Reynolds equation has been established. At the same time, the thermal energy equation and the temperature-viscosity equation have also been set up. The numerical calculation finite element model has been built to simulate the variation of oil film thickness, transmission torque, load capacity, pressure field and temperature field of the oil film. From the simulation results, the effect rules of the oil film squeezing, cross-section sizes and distribution of friction disc surface grooves, friction disc surface roughness and working oil temperature rising caused by the friction pair on transmission torque and load capacity are obtained.
The dynamic balance equation of the friction discs are established on the basis of force analysis. Flow balance equation of the hydraulic control system and dynamic balance equation of load are also built. Dynamic characteristics of the proportional relief valve used in the testing system are studied experimentally and its transfer function is set up. According to the characteristics of the speed regulating start, transfer functions of the proportional pressure control system and the proportional flow control system are established respectively. The dynamic response characteristics of the two systems are analyzed and compared. The results show that the proportional pressure control system is more suitable for speed regulating start of belt conveyor.
Speed regulating start characteristics of the PID control and the PID optimal control are deeply studied with the Harrision starting speed curve. The results show that the both cannot meet the demands of speed regulating start of belt conveyor. The output speed lags behind the given speed and there are fluctuations in output speed. On this basis, the fuzzy PID cascade control is presented and its dynamic response characteristics are analyzed. The Harrision starting speed curve is also simulated. The results show that the output speed can track the given speed more accurately and there are no fluctuations in output speed. It indicates the fuzzy PID cascade control is suitable for speed regulating start of belt conveyor.
To verify correctness of theoretical analysis and effectiveness of control strategy, the experimental equipment of hydro-viscous drive speed regulating start has been built. By using a PLC, the experiments have been carried out to verify the PID and the PID optimal control effect. The fuzzy PID cascade control effect is verified by using a singlechip. The experimental results show that the fuzzy PID cascade control can meet the demands of speed regulating start of belt conveyor. Not only the output speed can track the given speed more accurately, but also there are no fluctuations in the output speed. It also proves the correctness of the theoretical analysis. The effects of working oil temperature, load and starting time on speed regulating start have also been studied experimentally.
引文
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