Monday, March 7, 2011

PLC Based Control Software Design Process

The important design steps are summarized. Step 1 and 2 refer to the manufacturing system design process whereas step 3 indicate the mapping procedure from the CSD-FR to the CSD-DP domain.
Step 1a. Create module architecture from MSD-FR and MSD-DP domains:
The manufacturing system modular architecture indicates the physical components to be controlled. The modular architecture is not available a structural decomposition of the system exhibits the dynamic components.

Step 1b. Structural decomposition of the system to be controlled:
The identified physical components of structural decomposition gains elementary functional modules or actors. I/O ports are used to identify the boundary of each module. They indicate the data flow between functional units and refer to the incoming event/sensor or outgoing event/actuator signals.

Step 2. Create an ontology to identify the task-neutral system’s behavior (MSD-DP):
Define a suitable set of task-neutral observable states, in which the controlled manufacturing system could be. By this means, an ontology about the control system is created. The system states are a set of disjoint states of system components to be controlled, such as shuttle, gripper, rotary actuators, and linear drives. Each of those components has a discrete number of states. This step should be usually performed on the manufacturing system design stage since it describes the task-neutral behavior of the manufacturing system.

Step 3. Identify task-oriented CSD-FR and interpret them into transition of states (CSD-DP):
Identify the desired high-level functional requirements on highest level and interpret them into transition of states. For example CSD-FRx = “Transfer material bin from A to B” with CSD-DPx = “Transfer state”. In practice, each identified module has predefined high-level states, such as ”Initializing state”, “on/off-state”, “requesting state”, “recovering state”, et cetera. This step may be accompanied with selecting a state chart pattern of a domain database, wrapping up the task-oriented activities.

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