PLC在工厂自动化中的地位之所以如此稳固,原因在于:
PLC的技术具有长期的稳定,软硬件均应用方便,即插即用,价格适中,堪称工业控制的适用技术。
可以说当今工业控制所要求的能,PLC可满足85%至90%。其不足部分可用其它办法补充。近几年来PLC也在不断提高其技术内涵,融合了IT技术(包括以太网,因特网,无线网技术,现场总线技术,以及运用软件工程方法提升PLC的编程语言,开发全新的编程系统,等等)。
PLC在开放方面也有了实质的突破。前十多年PLC被攻击的一个重要方面就是它的专有,现在有了极大的改观。PLC采用了各种工业标准,如IEC 61131,IEEE802.3以太网,TCP/IP,UDP/IP等,各种事实上的工业标准,如Windows NT,OPC等。
PLC在硬件上也有长足进步。微电子技术的进展全都运用到PLC中,元器件的集成度越来越高,促使PLC成本下降和可靠提高。专为PLC的设计的PLC-on-a-chip芯片业已问世多年。PLC的产品在体系结构和操作系统上都有了质的变化,能大幅提高。一个机架上可装多个模块。也出现了以Web为基础的PLC系列产品。
PLC、软PLC、IEC 61131在中国的未来
传统的PLC制造业不会在可预见的未来在国内建立和发展。但不排除软PLC在近期和可预见的未来,完全有可能在国内形成一定的气候。软PLC的I/O完全可以利用主流及一些有生命力的现场总线的系列产品。强实时操作系统可采用Windows CE,NTE,VenturCom的RTX以及其它;只要它们能实现控制的时间确定,即保证能以时间高度一致的方式执行控制指令序列,并具有可预测的结果或行为。加入WTO以后,中国成为”世界制造工厂”的进程正在加速。我们有足够的理由相信,PLC、软PLC在中国的销售的年增长率会显著高于世界的平均年增长率。因此,对PLC、软PLC以及IEC 61131的推广应用,特别是高水平的技术支持变得十分重要。
随着现代工业的规模生产的发展,为提高企业的市场竞争力,引入管控一体化的体系结构ERP/MES/PCS,在国内已提到议事日程。作为基础自动化PCS层的主要工具-PLC的应对手段,应该是迅速加强PLC联网和通信开发能力,以及信息初加工的能力。在国内,就平均水平而言,精通或通晓PLC联网通信、PLC与计算机通信的技术,与今后的需要相比,还有不少差距。为此,急需采取措施,加强培训。CAMETA在这方面也应有所作为。
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