Rockwell Automation Control Systems, Mayfield Heights, Ohio

One of the most striking examples of an innovative approach to shortening the time from part design to production is occurring at DaimlerChrysler, and some of the other automotive manufacturers, in their body production systems. They are taking advantage of some of the newest software technology available from computer-aided design (CAD) vendors and other software suppliers such as Rockwell Automation Control Systems, of Mayfield Heights, OH, through its Rockwell Software brand, to integrate different plant-floor processes into a single simulation environment.

Often referred to us as digital factory, digital manufacturing, virtual machine design, or virtual factory, virtual manufacturing provides a way for engineers to develop, evaluate, refine, and simulate the use of a complex system entirely on a computer before any time and money are spent on the actual system itself. In essence, virtual manufacturing is the process of design and verification of manufacturing systems, incorporating the intended product before it is built. Thus communication channels can be opened between the production floor and the designers to allow for continuous product improvement. Three primary technologies are making this concept more realistic and affordable: CAD systems, 3D visualization, and hardware-neutral operating systems.

Mechanical CAD systems are dropping in price and becoming more accessible to lower-volume companies, while 3D visualization programs help design engineers understand changes that can be made early in the product design process to make the plant floor run more smoothly.

As 3D software entered the general market in the late 1980s, it became possible to describe part geometries in such a way that large cavities with sweeping curves could be accurately cut from the electronic representation of the part's surface. The automotive companies benefited by introducing cars with stamped fenders and other body parts that revolutionized styling.

The introduction of 3D solid modeling software, first on big UNIX machines and more recently on desktop PC workstations, has created the capability to make intricate cavities in molds. Electronic surfaces now have walls and thicknesses that can easily be manipulated as part of a single object. Part geometries can be translated into machining of molds that, when the two halves are mated, can precisely mirror the visualization of the part on the screen of the designer. Companies like Moldflow^TM provide the injection-molding industry with a suite of software tools that help connect the design process to the plant floor.

What was only available to high-end users before is now being provided through standard products in an "off-the-shelf" computer market. Specifically, Component Object Model (COM), implemented in the Microsoft operating system environment, has provided application interoperability that greatly enhances the user's set of capabilities (see figure). A system built up using COM technology now allows not only a transfer mechanism between two systems, but a truly interactive session with two systems from two different vendors, where data is mutually accessible and there is a common user interface. Moldflow's product that works with SolidWorks is a good example.

Perhaps the most compelling feature of object modeling is the idea that a behavior-- that is, instructions to tell the object to "do something" under certain conditions -- can be encapsulated in the object in addition to static parameters or attributes. This allows the designer to build a model that can have static and dynamic characteristics embedded in its representation (that is, the object). The virtual part can now interact with other objects in the system in a fourth dimension -- time. This collection of objects, suitably defined, can now simulate the performance of the part in the real world.

Systems such as Dynamic Designer, another plug-in to SolidWorks from Mechanical Dynamics, provide force and load simulation within the CAD environment. The SolidWorks COM interface allows Dynamic Designer to interact with the CAD 3D model directly. To a given part, the user can add characteristics like weight, material properties, and other attributes so that he can now run a simulation of its behavior in the real world.

The advances in the software industry have led many companies to make improvements in their own design processes. In the last four years, companies like Deneb and Tecnomatix have developed off-line programming for robots that allow full simulation in a virtual environment, including the translation of the part through space. Now the user can interact with a virtual robotic workcell and verify that his robot program did what he had intended. Typically, the components in the workcell (including the part or part components) already exist in some mechanical CAD environment and are available to these tools. However, to truly debug the robot program in a virtual world, the rest of the environment needs to interact dynamically with the motion of the robot. Clamps need to open and close; parts need to move in; humans need to start and stop processes. Today, these components are programmed in the virtual world through a combination of proprietary modeling languages and graphical interfaces. In the real world, these nonrobotic components are typically controlled with a programmable logic controller (PLC).

PLCs execute relay ladder logic programs that are input/output-specific and are usually written as the last step before startup. The mechanical designer at the machinery builder generates a timing chart, which diagramatically displays the sequence of the mechanical components of the machine, for the control engineer. And the designer, in turn, works from a process chart and floor plan that the end-user's process engineer has provided based on his unique knowledge of how to build the product.

DaimlerChrysler sponsored a demonstration of these two items at the IAM show a year ago. CATIA V5, in beta release at the time, was used to plan the workcell that was set up in the company's booth. A processing-planning tool, developed as an add-in to the CATIA architecture, was used to specify the behavior sequences of the nonrobotic components such as clamps and fixtures. The sequence also identified the interlocks with the robots in the workcell.

Because the object model was built up from the physical resources of the workcell, all items in the sequence were referenced by their names as objects in the CATIA system. Rockwell Automation, using newly developed Rockwell Software technology, was able to read in the timing diagram and convert it to PLC code. Finally, Deneb used the PLC code, executing in a soft controller, to drive the virtual workcell contained in their IGRIP product.

Rockwell Software Enterprise Controls^TM, currently still under development by Rockwell Automation, is intended to provide new capability to the machine and controls design customer. It will take the output of a mechanical design task -- the development of the object model and its associated behavior (sometimes expressed as a timing chart) -- and bring it into the controls development environment. Rather than convert the timing chart immediately to ladder logic, the system will allow the controls engineer to elaborate on the original intention of the upstream designer. The engineer can add mode behavior (manual, automatic, etc.), emergency responses, interlocks and safeties, exceptions such as bypass, and other control-specific information. The engineer can also link data reporting to the machine state information -- production counts, utilization, rejects, and other management information.

As a next step in the code development process, the specific devices that are available to do the necessary tasks can be selected. Embedded in the device descriptions is the I/O behavior of that device. Only the last step is concerned with I/O. The controls engineer then can create all the names and device-specific detail. Part of the use of object-oriented design permits the encapsulation of device behavior; these entities are called control assemblies. Also contained in a control assembly is information that can be used for generating wiring diagrams, diagnostics, and HMI. Finally, the system can generate code for several different controllers, based on some unique compiler technology embedded in Enterprise Controls.

For more information on Rockwell Software Enterprise Controls, contact the author of this brief, director Jim Coburn, at Rockwell Automation Control Systems, 1 Allen Bradley Drive, Mayfield Heights, OH 44124; (440) 646-7977; fax (440) 603-9031. This brief is adapted from a paper of the same title in the 1999 Proceedings of the National Manufacturing Week Conference. Copyright © 1999 Reed Exhibition Companies.

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