基于Petri网的柔性装配单元建模及PLC程序设计

Modeling of Flexible Assembly Cell And PLC program design based on Petri Net

将柔性装配单元的资源和操作表示为Petri网(PN)的库所和变迁,建立不会发生死锁的柔性装配单元PN模型。根据PN的变迁触发条件和标识变化规则,列出由资源、操作和条件组成的逻辑表达式,将表达式元素间的逻辑“与”、“或”关系和PLC梯形图的“串”、“并”触点相对应,可以方便地把逻辑表达式转化为PLC的梯形图程序。通过实例表明建立的柔性装配单元的PN模型可以有效的避免系统死锁,而且根据PN模型能够方便地设计出符合装配控制要求的PLC梯形图控制程序。

The resources and operations of flexible assembly cell expressed as places and transitions of Petri net （PN）. The PN about flexible assembly cell was unable to occurring phenomena of deadlock. According to the rules of transition firing and marking processing, we can formulate logical expressions composed of resources, operations and conditions. The ＂AND＂ and ＂OR＂ relations of elements in logical expressions correspond to serial and parallel connections in PLC LAD. Those expressions can be easily converted into PLC LAD program. Through an application example, The PN model of flexible assembly cell can effectively avoid deadlock in the system. According to the PN model, PLC LAD program was more easily designed in compliance with the requirements for controlling the assembly.