Research And Application Of Soft PLC Based On Open CNC System

Open CNC system is the key development direction in the field of numerical control system, but the traditional PLC has been unable to meet the requirements of open CNC system. Soft-PLC which was implemented in software based on PC has been an important technology in the practical application of open CNC system. In order to realize the specific control process for users, the shell script usual was used to assistant development, and through the HAL pins to operate the numerical control system to implement the control task during the application of full software CNC(EMC2). The development mode have some limitations, most of users do not have the ability to develop by this manner, and the control technology requires frequent adjustment during the trial period, which caused the application tasks of CNC system become heavy, development cycle become longer, and more difficult to maintain. These defects have hindered the application and promotion of CNC system in the market.In order to solve the above problems, the soft-PLC has been developed based on full software CNC, it lets users design their own operating procedures according to their demands by themselves. Its main contents are listed as follows.Firstly, according to the programming rules of ladder diagram which has been defined in the standard IEC61131-3, the editor of ladder diagram was designed and realized by Qt. Users of soft-PLC can edit or save, open programs of ladder diagram.Secondly, the strategy of transforming the ladder diagram based on two-dimensional array to instruct list was studied according to characteristics of the data structure which was used to save ladder diagram during the editing progress. The algorithm to directly explain and execute ladder diagram programs has also been designed and implemented.Thirdly, the modules of the running system to explain and execute ladder diagram programs was realized based on HAL of EMC2, which enable soft-PLC to read inputs, explain and execute ladder diagram programs, and renew output periodically. In a result, the axis control function of soft- PLC has also been realized.Finally, each of function modules of the soft-PLC has been tested, and also it has successfully used in a LED dispenser, the result of testing indicate that the LED dispenser can correctly accomplish the technological process.