Next step to quick ramp up: Virtual PLCs

Problem: The mechanical engineer knows how the production cell should function, but lacks an efficient means of delivering this knowledge to the control engineer who must write the PLC code.

Solution: Generate PLC programs directly from the virtual manufacturing environment using available 3D data.

In any manufacturing operation, production cell commissioning periods directly affect the speed with which a new product can be launched. Design changes or reworking of control programs may escalate cost and delay product to market. The result can be worse than lost income—it could mean lost market share.

The advent of virtual manufacturing cells, designed to graphically display and simulate actual manufacturing operations for analysis of process feasibility, collision avoidance, and bottlenecks or ergonomics, suggests the next logical step: Virtual commissioning or the ability to test and verify PLC programs prior to the machine or line build. The concept is straightforward. Why not use the 3D CAD data that comprises the virtual manufacturing cell to program its PLCs automatically?

Tecnomatix Technologies Ltd., in collaboration with Siemens Automation & Drives, makes this possible. The joint effort features new software entitled eM-PLC. Part of the Tecnomatix e-Manufacturing suite of software solutions, eM-PLC interfaces with Tecnomatix eM-Workplace on the front end and Siemens STEP 7 professional software, the programming package for SIMATIC PLCs, on the back end.

As a result, says Yoav Tomer, Tecnomatix product management director, the new software effectively bridges the gap between the mechanical design engineer, the process engineer, and the control engineer. The process engineer, he explains, uses eM-Workplace to create a 3D model of the manufacturing cell in 3D motion. Running on Unix or NT, the object-oriented software accepts product and tools data from multiple CAD systems, as it was designed by mechanical design engineers. Process engineers then define the behavior (as kinematics and motion properties) of all objects as well as the behavior of the complete manufacturing cell. Later on they can add to the model control information as interlocks, valves, and sensors via eM-PLC, both on Unix or NT.

"Today, the mechanical design engineer and the process engineer are becoming part of the same department," Tomer states. "If one makes a change, the other is notified. They share the same understanding of the process, they work together, and the software tools they are using can support that. What eM-PLC does is bring the control engineer into that same room."

This happens as follows: the object library of the mechanical designer and the control library are linked together by matching a function block (modeling the control behavior of an object) to the corresponding object. Then, based on the same data model from the mechanical design and process engineers (the manufacturing cell model, sequence of operations, and control-related information), eM-PLC will automatically generate the PLC program in Siemens STEP 7. By using the customer's own library of function blocks, the customer's programming standard on the PLC program (for manual mode, for example) will be automatically applied. Control engineers can then use eM-PLC to simulate and verify this PLC program in the virtual 3D model.

Later, a complete SIMATIC project—which includes the main programs, the sequence and the symbol table—is generated and can be downloaded to the PLC controller for use in the production line.

"During virtual commissioning, the virtual controller where the PLC program is running drives the manufacturing cell stimulation," explains Catherine Fritsch of Siemens Automation & Drives. "On the screen, the control engineer sees the virtual manufacturing cell and in parallel he can view what part of the code is being processed at any given time."

"And you don't have to change the code if there is a problem," Fritsch adds. "For example, if during testing you see a collision, you can add another interlock condition or change the sequence of operations. It is not necessary to rewrite the code. You simply go to the model, make the change, and download the new program. It's done right on the screen."

Using eM-PLC and STEP 7 to bridge the gap between the mechanical design engineer and the control engineer, says Fritsch and Tomer, will not only improve and standardize the quality of PLC programs, it will dramatically cut ramp up and commissioning costs—important news for all manufacturers.