Program Direction

For most installations, performing the assigned work automatically is the primary purpose of the machine controls. Auto Mode allows the control program to direct that work without requiring the operator to command each individual machine action.

The PLC Pro™ understands that the control program is responsible for directing the installation activity required to perform the assigned work while Auto Mode is active.

One of the main tasks in control program development is to determine which equipment functions are required to perform the assigned work and to coordinate how and when those functions are used.

While the installation is in Manual Mode, equipment actions originate with deliberate operator commands. The operator may request a cylinder to extend, a conveyor to run, a drive to change speed, or another defined equipment action. While he or she may be able to actually perform the assigned work this way, requiring an operator to command every individual action would make most production processes painfully slow and impractical.

Automatic operation does not require every part of the work to occur without human participation. Its practical value is that the operator no longer has to direct each individual machine action required to perform the assigned work.

The customer expects the completed control system to make the installation productive. That generally means performing the assigned work efficiently and repeatedly without requiring an operator to direct every individual machine action. Auto Mode is how the control program meets that expectation.

Automatic operation also provides consistency that may be difficult to achieve through individual operator commands. Once the required operation has been developed and verified, the control program can coordinate the same equipment functions with repeatable timing and execution from one cycle to the next.

Some assigned work cannot practically be performed in Manual Mode. Required timing, synchronization, positioning, or other process conditions may depend on the control program coordinating machine actions more quickly or precisely than an operator could accomplish through individual manual commands.

While Auto Mode is active, the control program is responsible for managing the installation activity required to perform the assigned work. It maintains direction of that activity as the work progresses.

The PLC Pro organizes the assigned work into defined PLC Pro Sequences. These sequences provide the structure the control program uses to manage the progress of the work, determining what must occur and when the requirements for progression from one part of the operation to the next have been satisfied.

PLC Pro Sequencing is intentionally standardized. Every PLC Pro Sequence uses the same defined structures for requests, operating permissives, activation, progression, completion, and reset.

Using the PLC Pro Sequence structure for every sequence does far more than simplify programming. Operators and maintenance personnel become familiar with the same conditions, terminology, and sequence concepts throughout the installation, and those same concepts are reflected in each element of the installation HMI. When an operation does not start, stops progressing, or behaves unexpectedly, everyone can approach the problem using the same questions and terminology. That consistency makes programs easier to understand, problems easier to diagnose, and the installation easier to operate and maintain.

Ultimately, the customer benefits from that consistency. PLC Pro Sequencing uses explicit, named, and cross-referenceable program elements so operators, maintenance personnel, and future PLC Pros can quickly determine the current step of a PLC Pro Sequence, what is allowing or preventing its progress, and where each part of its logic is used. The result is an installation that is easier to troubleshoot, maintain, modify, and support throughout its service life.

Not every requirement within a PLC Pro Sequence must be an automatically performed equipment action. A PLC Pro Sequence may require an operator to load a part, make a connection, supply a build element, initiate a cycle, or perform another defined task.

When operator participation is required, the control program uses HMI to inform the operator what is needed and coordinates that activity as part of the PLC Pro Sequence. Current-State feedback confirms when the required action has been completed, allowing the PLC Pro Sequence to progress just as it would after an automatically performed equipment action.

Whether the assigned work requires equipment actions, operator participation, or some combination of both, the control program remains responsible for managing that work. PLC Pro Methods use defined, standardized PLC Pro Sequences as the most effective way to organize that responsibility, providing a consistent structure for directing the work, evaluating its progress, coordinating participation, and supporting the people who operate and maintain the installation.

The required equipment functions are identified from the work the installation must perform. The PLC Pro breaks that work into the machine actions needed to accomplish it and assigns those actions to the appropriate PLC Pro Sequences.

For example, a workstation may use separate PLC Pro Sequences to load the workstation, perform the required processing or assembly, and unload the completed work. Each PLC Pro Sequence requests the equipment-level functions developed and verified in Manual Mode , selecting those required to perform its portion of the assigned work.

Each PLC Pro Sequence coordinates how and when its required equipment functions are used. Actions that are individually valid may need to occur in a particular order, wait for another activity to be completed, operate together, or avoid competing with another function or another PLC Pro Sequence for the same machine resource.

The PLC Pro Sequencing method defines the structure used to build and coordinate PLC Pro Sequences. Program direction identifies the work and equipment functions that must be managed; PLC Pro Sequences provide the structure for carrying out that work.

The assigned work may also depend on supporting resources such as hydraulic power, shop air, cooling, or another required service. These resources may be controlled by the control program, but they are often established independently of the individual PLC Pro Sequences that use them. When a resource is expected to remain available throughout an operation, the PLC Pro normally treats its required availability as a permissive condition rather than as an equipment function commanded by each PLC Pro Sequence. That condition is evaluated at the level where the resource is required, such as Auto Mode, OK to Start, or OK to Continue.

• Make the control program responsible for directing the installation activity required to perform the assigned work while Auto Mode is active.
• Determine the equipment functions required to perform the assigned work and coordinate how and when they are used.
• Organize assigned work into rational, clearly defined PLC Pro Sequences that use the applicable equipment-level functions developed and verified in Manual Mode.
• Use the same defined PLC Pro Sequence structure for every automatic sequence.
• When operator participation is required within a PLC Pro Sequence, use HMI to identify the required action and use Current-State feedback to confirm its completion before dependent sequence progression occurs.
• Evaluate whether supporting resources needed for an operation should be treated as permissive conditions.