【作者】 卞和营；

【导师】 杨承；

【作者基本信息】 西南林学院 ， 载运工具运用工程， 2007， 硕士

【摘要】 在电液伺服控制系统或电液比例控制系统的常规应用中,通常把传感器接入厂家提供的放大器的传感器接口,组成连续时间的闭环控制系统。这种系统的指令输入是模拟信号,传感器输入到放大器接口的信号也是模拟信号,所以这种系统是一种模拟量闭环控制系统,并且这种系统的调整也比较简单,但是现代的各种高级智能控制在这种连接形式下却难以实现。随着计算机技术的迅速发展,计算机控制技术得到逐渐推广应用,特别是PLC,作为控制用计算机中一种,在工业自动化中得到广泛应用。现代的PLC已经具有相当的计算功能,但在现代实际应用中,相当多的PLC只是作为对放大器提供指令信号和进行普通逻辑控制的简单工具,并没有深入开发PLC的潜能。本来在现代PLC中,机内虽然已经提供了能进行闭环PID调整的软件,以子程序的形式调用,就可以灵活地对PID参数进行调整,但这种形式只能局限在PID调整控制中,难以进行高级的智能控制。要在现有的设备基础上,应用现代兴起的各种高级控制方法,提高控制系统的控制精度,只有把传感器反馈接口接入PLC,组成一个实际的计算机控制系统,这种控制系统与连续控制系统相比较,具有明显的优势。但这种计算机控制系统,只能接受和处理二进制代码,用这些二进制代码来表示某一种物理量的大小或某个数值,也即所谓数字信号。所以在这种系统中首先就是对实际系统中的连续量进行采样和离散化处理,成为现代控制中的离散化控制系统,更精确地说是采样控制系统。然而根据应用PLC组成的实际控制系统的模型,怎样对这个采样闭环控制系统进行正确的建模、仿真与分析,尔后用于实际的控制系统是当前自动控制系统研究者们正在进行的工作,并且当对实际的系统进行正确的建模和分析研究后,还可以把各种高级控制方法如智能控制等应用到实际控制系统中。因此,本人的研究工作,不仅为将来相关系统的研究开发奠定了理论基础,而且论文中根据理论求得的采样周期T的范围的方法及其对实践的指导意义也值得在实践中进一步推广和应用。本文在总结前人研究的理论基础上,应用西门子的PLC作为控制器,比例阀与油缸作为被控对象,激光传感器作为反馈元件自行设计了电液位置闭环采样控制系统。该系统中的控制器PLC的CPU226只接受和处理数字形式的信号,所谓数字信号是相对于连续(模拟)信号而言的,其信号复制只取有限多个离散值;系统中的被控对象比例阀与油缸的运行是连续的;所以研究系统实质上是一个闭环采样控制系统。研究过程为:第一、对实际的电液位置闭环采样控制系统的电气部分和液压部分进行认真检查,避免系统中电气部分的短路和液压部分油路的泄漏或堵塞,保证系统的工作性能稳定。第二、认真地分析控制系统中的各个环节,如比例阀、油缸和传感器,并参考相关的理论知识给出了它们各自的传递函数,特别是对系统中的PLC进行了更加详细地分析,不仅分析了PLC对信号的处理过程,而且给出了PLC中零阶保持器的传递函数。第三,画出了实际采样控制系统的框图,由于z算子与时间有更为直接的联系,可以直接应用于计算机采样控制系统的计算,所以采样控制系统理论中是应用z算子来表示传递函数的。因此,本文运用采样控制系统的理论得出了开环与闭环采样控制系统的Z传递函数,作为分析整个采样控制系统的基础数学模型。并在此基础上应用Z传递函数和开环Bode图求出了采样周期T的两个范围。第四,运用SIMULINK对采样控制系统在不同的采样周期时进行仿真,仿真结果是在0＜T＜0.1633s的范围内选取采样周期时能够保证系统稳定且没有振荡产生;而在0＜T＜0.6277s的范围内选取采样周期时,随着采样周期T的增大则系统的振荡加剧,信号失真,将有可能造成系统的不稳定;在所求得的T的范围外进行仿真时系统是发散的,即系统是不稳定的。第五,在仿真的基础上对实际采样控制系统进行实验,实验结论是通过对多种不同采样周期的数据分析,可知系统随着采样周期T的增大超调量增大,系统将振荡趋于稳定或振荡趋于发散。第六,把实验结果与仿真进行了比较,发现实际系统中由于比例阀死区的存在,如果对比例阀的死区不进行补偿,油缸将无法到达预定目标,因此,论文最后给出了补偿的方法并提出了本研究中需要改进的地方。更多还原

【Abstract】 In electro-hydraulic servo control system or electro-hydraulic proportion control system’s routine application, generally connect the sensor to the port of electrical amplifier, constitute continuous time closed-loop control system. And this systematic command input is analog signal, the signal which sensor input electrical amplifier is also analog signal, therefore, this kind of system is regarded as analog closed-loop control system, this adjustment of system is also fairly simple, but modern high-level intelligent controls is difficult to come true under this form linking up. With the quick developing of computer technology, the computer control technology is extended application gradually, especially PLC, as one kind of controlling computer, getting extensive use in the industrial automation. Modern PLC has already the complicated calculation function, but in modern actual application, many PLC are only as the simple tool which provides the command signal and carry out the general logic control. Through correct programming at present, PLC has already being able to carry out closed-loop PID adjustment by the subroutine has been called. But the form can only limit the PID adjusting and not apply high-level intelligent control.Be going to base on the available equipment, applying the modern high-level various control method being on the rise, improves the control accuracy of control system, only insert the sensor’s feedback interface into PLC, constitute an actual computer control system, this control system has obvious superiority when comparing with the continuous control system. But this computer control system can only receive and handle binary code, use these binary code to express some one kind of physics amount size or some numerical valve (digital signal so-called). Therefore, in this system it is first sampling and dispersing to continuous amount in actual system, becoming disperse control system of modern control, more accurate speaking it is sampled-data control system. However, according to actual control system model that is composed of PLC, how to carry out correct building model, simulation and analysis on sampled-data closed-loop control system and apply it to actual control system is the job that current auto control system researchers are carrying out, and being able to apply high-level various control such as intelligent control to actual control system after correct building model and analysis on actual system. Therefore, not only do my research establish theory foundation for the future relevant system research and development, but also do the sampled-data period T range method and the guiding significance to practice deserve being extend and being applying to practice.Based on former theory research in this field, PLC applying Siemens’s is a controller, proportional valve and hydraulic cylinder are member controlled, and the laser sensor as feedback component designed electro-hydraulic position closed-loop sampled-data control system by self. Owe controller PLC CPU226 in system only receive and handle digital form’s signal, the so-called digital signal is relative to continuous signal, it’s signal duplication chooses only limited discrete valve, while the controlled member proportional valve and hydraulic cylinder is continuous, therefore, studying system is a closed-loop sampled-data control system.Study process is: first, carry out conscientious examination on electricity part and hydraulic part of electro-hydraulic position closed-loop sampled-data control system, avoid electricity part short circuit and hydraulic part leakage or block, ensure the system’s service behavior is stable. Second, analyze each segments of control system seriously, such as proportional valve, hydraulic cylinder and sensor, give them out respective transfer function under relevant reference theory knowledge, analysis having been especially detailed to PLC, not only analyses the PLC treatment process to the signal, moreover give out transfer function of zero-order hold in PLC. Third, have drawn the block diagram of the actual sampled-data control system, since the Z operator and time have being more direct relation, can be directly apply to the computer sampled-data control system calculation, therefore, this paper reach the Z transfer function of opened-loop and closed-loop sampled-data control system by applying sampled-data control system theory, and as the basis mathematic model analyzing entire sampled-data control system. Fourth, carry out simulating to sampled-data control system under the different sampling period by applying SIMULINK, simulated result is able to ensure that system stable and oscillating does not come into being when choosing the sampling period within 0<T<0.1633 second range; when choosing the sampling period within 0<T<0.6277 second range, with sampling period T enhancing is that system oscillating is aggravated, the signal is distorted and system may bring about instability; The system is unsteady when choosing the sampling period outside 0<T<0.6277 second range. Fifth, carry out an experiment on actual sampled-data control system on simulated basis, the experiment conclusion is the data analysis by taking different sampling period ,may know surpassing amount of the system will enhance with sampling period enhancing and system tends to become oscillating stabilizing or oscillating unsteady. Sixth, since proportion valve exist dead area in actual control system, discovery hydraulic cylinder will have no way to get to the target fixing in advance if the dead area of proportional valve is not compensated when comparing experiment conclusion with simulated result. Therefore, the conclusion has given out method compensated and has brought forward the place need be improved.更多还原