基于N叉树的PLC功能块向指令表的转换算法研究

Research on the conversion algorithm of PLC function block diagram to instruction list based on nary trees

针对软PLC多重输出的问题,提出了基于N叉树的PLC功能块图向指令表的转换算法。该算法首先将功能块图映射为N叉树型数据结构,在此基础上通过对N叉树结构进行了分解重组,将生成的复杂树结构分解成多个有序子树结构的集合,再对分解后的树型结构依次进行了后序遍历方式访问,根据不同的节点类型转化编译成相应的指令表语言,实现了PLC功能块图形语言向指令表的转换。文中给出了一个转换实例,阐明了该算法的思想及其实现步骤。并在基于IEC61131-3准则的软PLC上位机系统进行了实验验证,实验结果表明该算法具有通用性,能够将具有多重输出的复杂控制逻辑功能块图转换成指令表语句,在编译转换过程中,该算法很好地简化了程序,节省更多的内存空间,提高了PLC功能块图编译转换的效率。

Aiming at the problem of multiple output of the soft PLC, the conversion algorithm of PLC function block diagram （FBD） to in- struction list （IL） based on Nary Trees was proposed and implemented. In this algorithm, firstly, the FBD program is mapped to the Nary Trees. On this basis, through decomposition and reorganization of the Nary Trees, the complex tree structure generation was decomposed into a collection of ordered subtree structure. And then the decomposed tree structures are sequentially visited in the post-order traversal way. Depending on the different nodes types which are translated into the corresponding IL, the PLC FBD, finally, was achieved to be converted to the IL. An example was given to illustrate the ideas and implementation steps of the algorithm. Experimental verification of soft PLC host computer system ,based on the 1EC61131-3 international standard, was carried out. The experimental result shows that the algorithm is a general conversion algorithm for conversion of complex FBD with multiple outputs into IL. And in the process of the conversion, the algorithm can preferably simplify the procedures, save more memory space and improve the efficiency of PLC FBD compilation conversion.