Research And Development Of Soft PLC Based On LinuxCNC

With the rapid development of science and technology,PLC technology has received wide application in various fields.In recent years,soft PLC technology is the critical direction of PLC technology development due to its characteristics such as open structure,standardization,intelligence,etc..In the field of soft PLC technology research,comparing with western countries such as Europe and the United States,the related research in China is still in the development stage.Therefore,developing a soft PLC system with independent intellectual property rights is significant to improve the level of industrial automation.In this paper,based on the software structure of the open CNC platform LinuxCNC,we develop a set of soft PLC application software to realize the logic control of CNC machine.Soft PLC system includes three components: the programming module,the running module and the simulation module.Through using graphical programming tools Qt development,the programming module designs the main interface module,resource manager,ladder components library and the storage structure of ladder and instruction table,and achieves some functions,such as the ladder diagram display,ladder diagram editing and transforming ladder diagram to instruction list.To achieve the capability of transforming ladder diagram to instruction list,firstly,mapping the ladder diagram into a directed acyclic graph and storing the graph information with the cross linked list data structure.Secondly,getting the binary tree containing the ladder logic relation by designing the concatenated and parallelized algebraic algorithm.Finally,traversing the binary tree to get the instruction list.The operating module,Based on Linux CNC hardware abstraction layer development,uses shared memory to communicate with programming module.Additionally,we utilize the first-in-first-out principle of stack structure,which was realized by a array in the kernel space to achieve the function of instruction list parsing execution.The simulation module adopts the object-oriented way to develop and realizes some functions of simulation components,such as online addition and deletion,arbitrarily drag-and-drop,save and load.In this way,the simulation programs and layouts can be freely changed according to the real need of users.Finally,the accuracy and stability of the soft PLC system are verified by applying it to the PCB placement machine.At present,the soft PLC system has been commercially available,which has a good market competitiveness.