1. Field of the Invention
The present invention relates generally to programmable logic controllers and, more specifically, to a method of application protocol monitoring for programmable logic controllers for manufacturing a motor vehicle.
2. Description of the Related Art
It is known that programmable logic controller (PLC) code is written by controls engineers after assembly tooling designs are completed and a manufacturing process has been defined. Once the programmable logic controller code is written, it is used by programmable logic controllers to control and monitor machine tools used in the manufacture of parts and assemblies for motor vehicles.
It is also known that a manufacturing line is typically made of three to twenty linked workcells. Each workcell consists of a tool such as a fixture to position a product, for example sheet metal, and associated automation, for example robots, that process the product, for example by welding. The workcell typically consists of a fixture/tool surrounded by three or four robots. The product is then transferred to the next workcell in the manufacturing line for further processing, until it exits the manufacturing line.
A major problem faced during launch of a vehicle and new equipment start-ups on the manufacturing line is assuring that various devices receive the appropriate control signals. In the past, the devices were interlocked via signal lines or electrical wires with low voltage discrete signals. To determine whether appropriate signals were received, an operator used a voltmeter to measure whether a specific device received a discrete voltage signal. But with the increasing use of networks to replace the individual signal lines, this transaction is less visible. Frequently, multiple and different software monitoring tools that are specific to the various devices are used on a network to watch the effect of signals passing from one device to another. Current network monitoring tools can detect the presence and values of control I/O “tags” that are being communicated through an Ethernet of a manufacturing plant for the motor vehicle. However, these network monitoring tools do not have the capability or information required to determine if the “tag” value is correct (expected) or if the tag values should even be present (active at a particular time or setting a dependency).
Therefore, it is desirable to provide application protocol monitoring for programmable logic controllers. It is also desirable to provide a method for establishing and monitoring data tables of a manufacturing line, rather than an isolated data table of a programmable logic controller. It is further desirable to provide a method of protocol monitoring for viewing I/O “tag” activity for tooling and workcells of a manufacturing line. Therefore, there is a need in the art to provide a method that meets at least one of these desires.