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1、 A Monitoring System For PLC Controlled Manufacturing System Based On Fieldbus1. IntroductionThe winding vacuum systems for plating metal such as zinc and aluminium on thin film are very common in the capacitance industry. The main goal is to increase as much as possible the film transport velocity
2、while controlling the tension of the film. The tension and the speed of the film should be maintained at a reference value. The main concern is the coupling existing between film velocity and tension. There exist many sources of disturbances on the velocity (roller non-circularity, film sliding). If
3、 the delivery speed fluctuates, then the treatment on the film becomes nonuniform. On the other hand inappropriate tension may cause wrinkles or even a film break. Once film break takes place, the operator needs open thewinding chamber again. Obviously the pressure of winding chamber comes back to s
4、tandard atmosphere pressure. And it will take about 20-30 minutes for winding chamber to reach the required pressure. Accordingly the output will decrease evidently. So a monitoring system to monitor tension fluctuation in order to avoid film break is very needful.CC-Link is a field network system t
5、hat processes both control and information data at high speed, to provide efficient, integrated factory and process automation. Using CC-Link enables users to reduce the amount of control and power wiring required in the complicated production line. Since users can select the suitable devices from m
6、ore than 354 field devicessupported CC-Link it is easy to expand multi-vendor environment.As for the communication of speed, this enables the communication with the sensor input which requires a high speed response and intelligent devices which requires a large amount of data communication.As one of
7、 CC-Links features, RAS functions such as, stand-by master function, detaching slave station function and auto return function enable recovery from the communication fault and the system debug at start up time.As for test and monitoring function, confirmation of the data link status, hardware test a
8、nd circuit test are available. The CC-Link network diagram is shown as Fig. 1. The CC-Link monitoring system is composed of master station slave stations personal computer inverter servo motors remote I/O units, ect.In order to meet the quest for automation and flexibility, many complex manufacturin
9、g systems are controlled by Programmable Logical Controllers(PLC). This is because that PLCs are adaptable, modular, user-friendly and acquired at low cost. And that winding vacuum film plating system is just such a complex manufacturing system.The paper presents an intelligent monitoring system bas
10、ed on CC-Link fieldbus which consists of upper personal computer and the lower Programmable Logic Controllers for the aim of control and information management. A new kind of technology using CC-Link fieldbus is adopted in this monitoring system.2. Structure of The Monitoring SystemThis fieldbus-bas
11、ed monitoring system has two arrangements including monitoring units in field and information management and control unit in control room. All intelligent monitoring units located nearby the winding vacuum machine have microprocessors, which have the following function as respective signal sampling,
12、 A/D conversion, data calculation, ect.Fieldbus is the most important connection between each discrete monitoring unit in slave stations and master station. Analog signal is superseded by digital signal for bi-directional communication. It is beneficial for an operator to realize control, verificati
13、on and parameter setting in control room. The kind of structure, on one hand, increases the precision and antiinterference capability of the monitoring system. On the other hand, it saves the investment cost.The quantities of intelligent monitoring units should be determined by practical needs. This
14、 system has five kinds of monitoring units: temperature, vacuum degree, roll diameter, film tension and transfer velocity.Whether the monitoring system could work normally depends on the performance of the sensors to a considerable degree. Their precision and stability has a direct influence on the
15、monitoring system. Data obtained from these sensors are processed by PLC and displayed on HMI as Fig. 2 shown.Intelligent monitoring module has two functions: on one hand it filters,amplifies and adjusts the output signal got from sensors to appropriate value which can be processed by PLC (FX series
16、). On the other hand it carries through signal sampling, A/D conversion, data processing, software antiinterference,parameter calculation and transmits data to central control unit by virtue of communication interface of a PLC. Central control unit (CCU) is the center of this monitoring system which
17、consists of PC and RS232. It takes control of working condition of each intelligent monitoring unit, gets data and abnormal information and saves them. In addition, CCU can be visited by upper user computers. Furthermore,it has been practicable to analyze data and give a diagnosis for winding system
18、 by taking advantage of data management and fault diagnosis software.The monitoring system makes use of CC-Link fieldbus which consists of communication module and twisted-pair wire acting as communication medium. Sixty-four stations could be connected to this kind of fieldbus at most. The communica
19、tion module is connected with monitoring units and respective stations through CC-Link fieldbus. Transmission distance even reaches 1.2km while communication rate of fieldbus is 156kpbs.3. PLC PROGRAMMINGIn this winding system, we use Mitsubishi A series PLC as master station PLC because it has the
20、characteristic of quick response and great ability of information processing. It is used to control the behaviors of the total winding system together with FX series PLCs of winding and unwinding system. The operating actions of the system and the sequence of these actions were edited beforehand int
21、o the control program by the designer. The control program sets a series of operations of the winding system, which tells the PLCs how to control a system. The current states of all sensors or actuators are saved as an array of input, output or flag signals in the PLC memory. Therefore, the PLC prog
22、ram is the basis of monitoring in a PLC controlled manufacturing system. The programming method used is the ladder diagram method. The PLC system provides a design environment in the form of software tools running on a host computer terminal which allows ladder diagrams to be developed,verified, tes
23、ted, and diagnosed. First, the high-level program is written in diagrams. Then, the ladder diagram is converted into binary instruction codes so that they can be stored in random-access memory (RAM) or erasable programmable read-only memory (EPROM). Each successive instruction is decoded and execute
24、d by the CPU. The fimction of the CPU is to control the operation of memory and I/O devices and to process data according to the program. Each input and output connection point on a PLC has an address used to identify the I/O bit. The method for the directrepresentation of data associated with the i
25、nputs, outputs, and memory is based on the fact that the PLC memory is organized into three regions: input image memory, output image memory, and internal memory4.The PLC program uses a cyclic scan in the main program loop such that periodic checks are made to the input variables. The program loop s
26、tarts by scanning the inputs to the system and storing their states in fixed memory locations (input image memory). The ladder program is then executed rungby-rung. Scanning the program and solving the logic of the various ladder rungs determine the output states. The updated output states are store
27、d infixed memory locations (output image memory). The output values held in memory are then used to set and reset the physical outputs of the PLC simultaneously at the end of the program scan4.As we know, logic control is a remarkable property of PLC, and it can be applied to efficiently handle anal
28、og data2.1) Analog data acquisition and transformationAnalog inputs and outputs such as pressure and temperature need to be measured on-line. For instance, temperature is first acquired by the Platinum resistances. A signal transformation module then converts the measured resistance value into the v
29、oltage range of 1-5V. The output of this transformation module is finally collected and transmitted back to the above PLC.2) PLC control algorithmsThe analog variables could be any controlled variable, e.g., temperature or pressure in our winding system. As a matter of fact, there exist two control
30、modes, auto and manual. In the manual mode, operators modify the output values according to the desired levels; while in the auto mode, output values are regulated by the pre-designed control algorithms. It is worthmentioning that the outputs of PLC are always incremental values. Although auto-tunin
31、g PID controllers can be employed here, manual tuning is always used at the beginning of the production for routine initialization, and after that the system is switched to the auto mode. We emphasize that users experiences oriented fuzzy logic controllers are utilized here to further improve the pr
32、oduction performance as well. A film tension control system using fuzzy logic controller (PLC) on PLC to cope with the winding system uncertainty is proposed. Fuzzy logic algorithm is realized by basic PLC instructions.To deal with the system with fixed model and parameter conventional PID is enough
33、, but fixture is relative, in fact, the parameters of the winding system are variable in a definite range, therefore the controller must has robustness to obtain high performance. For this purpose, fuzzy reasoning is used to adjust the factors of PID, by this way the PID factors can be adjusted acco
34、rding to the changes of system state and plant parameters.3) Servo motors controlAt the beginning the film is transferred at a low speed, and then the servo motors are accelerated to set speed to wind at high speed at about 8 miles per second. The film tension is detected by load cells which control
35、 servo motors velocity to keep tension constant. The objective of control is not only to keep film tension constant but also to make winding velocity arrive at set value at least time. So the main problem is how to control servo motors accurately.4, CONCLUSIONA monitoring system for PLC controlled m
36、anufacturing System Based on fieldbus for film plating production process is presented in this paper. It has been successfully on operation in practical production since 2003. Promising results have demonstrated its great advantage in practice as well as significant profit improvement. 基于现场总线监测系统的PL
37、C控制制造系统1 导言用电镀金属做成的蜿蜒的真空系统，就像是锌和铝薄膜那样是非常普遍的电容行业。他的主要目标是当控制张力的膜时能尽可能增加膜的运输的速度。膜的紧张程度和速度应该以一个参考价值而被保存起来。而主要的问题存在于膜的速度和张力之间的耦合。它们之间的速度问题存在很多干扰资源（辊非圆，膜滑动）。如果传递的速度变动的话，那么对膜的治疗将会变的不均匀。另一个方面，不恰当的紧张局势将会导致褶皱或者是膜破裂。一旦发生膜破裂，经营者需要再次开放清盘商会。很明显，清盘商会的压力将会反作用于标准大气压的压力。而要达到清盘商会所需的压力需要20到30分钟的时间。因此，产量将明显减少。所以，用一个监测系统
38、，监测紧张的波动程度，以避免膜破裂是非常必要的。CC-Link是一个外地网络系统，它以高速传送控制力度和数据信息，以提供效力，结合代理，过程自动化。使用CC-Link可以使使用者减少数量控制和需要在复杂的生产线下的电源线路。当用户可以从支持CC-Link的多余的354个领域的设备中选择出合适的设备，那么多供应商环境的扩展将会变的很容易。至于交流的速度，使得通信和传感器输入需要高速反应和智能设备，需要大量的数据通信。作为一个CC-Link的功能，FAS的功能是：tand-by的主功能，分离站的功能，自动分离功能，这些功能使得在通信故障和系统调试时自动恢复过来。至于测试和监测职能，对确认数据连接状
39、态，硬件测试和电路测试都是可行的。CC-Link的网络图显示如图1所示。CC-Link的监测系统是由主站，奴隶站，个人电脑，逆变器，伺服电机，远程I/O单元等组成。为了满足追求自动化和灵活性的要求，许多复杂的制造系统都是由可编程控制器（PLC）来控制的。这是由PLC的适应性强，模块化，便于使用和成本低等优点决定的。真空卷绕镀膜就是这样一个复杂的制造系统。本文介绍了基于CC-Link现场总线的智能监控系统，其中包括个人电脑和目的是控制和信息管理的可编程逻辑控制器。使用CC-Link现场总线提出了一种新技术是为了通过这一监控系统。2结构监测系统基于现场总线的监测系统有两个安排，包括在领域里的监测单
40、位，信息管理和在控制之中的控制单元。位于清盘真空机附近的所有智能监测单位都有微处理器，其中有以下功能，各自的信号采集，A/D转换，数据计算等等。奴隶站和主站之间的每个离散监测单位是现场总线最重要的部分。为了进行双向通信，模拟信号被数字信号所取代。这有利于运营商在控制室里进行控制，核查和参数设置。这样的结构，一方面，提高了监测系统的精度和抗干扰能力，另一方面，它也节省了投资成本。 图1 CC-Link的网络图数字职能监测单位应取决于实际需求。该系统有五种监测单位：温度，真空度，轧辊直径，膜的张力和转移速度。监测系统是否能够正常工作在很大程度上依赖于高性能的传感器。其精度和稳定性，直接影响了监测制
41、度。从这些传感器上获得的数据经过PLC的处理，显示在人机界面上，如图2所示。智能监测模块有两个功能：一方面，它的过滤器，放大和调节输出信号的传感器通过PLC的处理可以得到适当的值（FX系列）。另一方面，它凭借通信接口的可编程控制器进行数据采集，A/D转换，数据处理，软件抗干扰，参数计算等将数据传输到中央控制单元。中央控制单元（CCU）是这个监测系统的中心，其中包括PC机和RS232。它的工作状态是控制智能监测的每个单位，将得到数据和异常信息进行处理以挽救它们。此外，控制器可以被用户计算机所访问。并且，它已经切实可行的分析出了数据，并且利用数据管理和故障诊断软件对数据进行了诊断。该监测系统利用C
42、C-Link现场总线构成的模块和双绞线作为通信介质。最多可以有64个站可以连接到这样的现场总线中。该通信模块是通过CC-Link现场总线与检测单位和各个站连接起来的。当现场总线的通信速率为156kps时传输距离可以达到1.2公里。 图2 在HMI上的监控显示3 PLC的编程在这个系统中，我们使用三菱系列的PLC作为PLC的主站，这是由于它的快速反应和巨大的信息处理能力的特点所决定的。它是用来控制总卷绕系统与FX系列的PLC缠绕系统和舒展共存系统的行为的。系统的经营行为和这些行为的排列都是由设计者事先编辑好的。控制程序规定了一系列卷绕系统的行动，讲述了PLC是如何控制系统的。目前国家的所有传感器
43、或执行器都被作为一系列的输入，输出和旗帜信号而保存在PLC的内存中。因此，PLC程序是在PLC控制的制造系统中的监测基础。PLC的编程采用梯形图的方法。它提供了一个设计环境，这个环境就是软件工具运行在主机终端，以便于梯形图的开发，验证，测试和诊断。首先，高层次的计划使用图表，然后，梯形图转换成二进制指令代码，以便于它们可以存储在随机存取存储器（RAM）或可擦除可编程只读存储器（EPROM）。每个指令由CPU解码和执行。CPU的程序是用来控制操作的内存和I/O装置，并根据程序处理数据。PLC上的每个输出和输入的连接点上有一个地址用于I/O位的识别。数据的直接代表的方法与输入，输出和记忆有关，基于
44、这样一个事实，将PLC的内存分为三个区域：输入图像存储，输出图像存储，内存。PLC程序采用主程序循环扫描的方法，例如输入的变数定期检查。该循环项目的启动是采用扫描输入系统和存储器在内存中的固定位置的方法进行的（输入图像记忆）。其它的程序是按照一个接一个的方式执行的。扫描程序和各种梯形量的解决决定了输出量。更新的输出量存储在固定的内存中（输出图像记忆）。在程序结束时，内存中的量被用来设置和从新设置PLC的物理输出。正如我们所知，逻辑控制器是PLC的一个重要组成部分，它可用于有效处理模拟数据。1）模拟数据采集和转换模拟的输入和输出就像是压力和温度需要在线测量一样。举例来说，温度是测量铂的电阻以获得
45、的所需要的量。经过信号转换模块转换后，测量电阻的电压值在1-5V之间。输出模块的这种转变是最后收集然后再返回给PLC的。2)PLC的控制算法模拟量可以是任何形式的变量，如我们的卷绕系统中的温度和压力。事实上，存在着两种控制方式，自动和手动。在手动模式下，运营商可以根据期望的水平修改输出值，而在自动模式下，输出量受预先设计的控制算法所规定。值得一提的是，PLC的产出总是增加的。虽然PID的控制器可以被控制在这里，但手动谐调的生产初始化一开始时就被使用，而且，在那个系统之后就切换到自动模式。我们强调，用户的面向模糊逻辑控制器的使用的经验，也能进一步改善这里的生产性能。膜的张力控制系统采用PLC的模
46、糊逻辑控制器（PLC）,以应付卷绕系统的不确定性。模糊逻辑计算法，实现了基于PLC的指示。 对于固定的模式和常规PID的参数处理已经达到了一个很好的阶段了，但是事物总是相对的，事实上，卷绕系统的参数设定在一定范围内，因此，控制器必须具有鲁棒性，以获得较高的性能。为此目的，模糊推理被用来调整PID的因素，用这样的方法，PID的因素可以根据系统状态和植物参数的变化来衡量。3)伺服电机控制膜一开始时是以很低的速度转动的，然后伺服电机开始加速，最后大概达到每秒钟8英里。膜的张力是由负载细胞控制的，它控制伺服电机以保持张力恒定。控制的目标不仅是保持膜的张力不变，而且也使绕组在最少的时间内达到设定的值。所以主要的任务是如何控制伺服电机能准确的工作。4 结论PLC的监测系统是用于控制制造系统的。基于现场总线的镀膜生产过程在本文当中已经给了很充分的说明了。自从2003年以来它已经在实际生产中得到了运用。它的成果已经证明了它具有很大的优势，而且它在实践中的利润也将会有很大的改善。