GM and OMAC in partnership

Manufacturing Engineering, Jul 1998 by Yen, Jerry

The biggest of the Big Three goes beyond the PC

The computer industry has demonstrated the tremendous advantage of open, modular computing systems. They improve system reliability and reduce costs by creating intense competition for every component. This understanding of other industries has driven GMPT to create, promote, implement, and support the open, modular architecture controls (OMAC) concept.

A common, open controller platform benefits any business that needs industrial controls. Current proprietary control systems make integration of inhouse technologies very difficult. A company can achieve a competitive advantage by incorporating its own in-house engineering knowledge in open controllers, resulting in more flexible, more capable manufacturing processes. Also, OMAC permits users to leverage the rapid technology advances and large sales volume generated by the personal computer hardware and software markets.

OMAC systems should reduce the costs associated with a control system-not just minimizing the initial purchase cost of a control, but minimizing the total cost of the system over its life cycle. Market forces operating in the personal computer industry will drive down initial implementation costs of control products. Because open, modular systems allow incremental upgrades and easy integration of components, the cost of making changes to a control system will also decrease.

Additionally, flexible manufacturing systems are becoming increasingly critical for manufacturers. From a mechanical perspective, manufacturing systems must be open, modular, and scalable. Integrating open, modular control components with open, modular mechanical components will make manufacturing systems reconfigurable and adaptable to changing application requirements.

OMAC-based manufacturing systems provide the same reliability as systems based on proprietary controllers. They must be maintainable with maximum uptime and minimum repair time to satisfy the requirements of a plant environment.

Defining an OMAC System. Definitions of several important terms relating to an OMAC system, published in the initial OMAC white paper in 1994 (see Table 1), reflect the OMAC concept at GMPT. Two important elements in the definition of "open" are the requirement for a "de facto" standard environment, and the availability of commercial control hardware and software components.

In today's marketplace, the Microsoft Windows environment is the de facto standard. Even though not designed to support real-time control applications, the Windows platform products NT, 95, and CE certainly can support many control functions. Now that Microsoft intends to make Windows CE a hard real-time operating system, the Windows environment looks even more suitable for industrial automation applications.

An OMAC-based system uses standard interfaces: common application programming interfaces (APIs) for control software modules, device level networks, digital drive interfaces, and higher level network interfaces. What interfaces should be standardized? If we define interfaces at too high a level, end users can't achieve the benefits that they want. On the other hand, if the interfaces are defined at too detailed a level, the definition may restrict technology innovation and limit or prevent competition among vendors.

To address this issue, the OMAC Users Group was formed in 1997. It includes end-user companies, technology suppliers and integrators, and OEMs. One achievement of this group is cooperation with Microsoft to ensure incorporation of hard real-time requirements for industrial automation in the next version of the Windows CE operating system.

What About PCs? A PC front end can't meet the goals of OMAC. Implementing a PC front end provides network connectivity and graphical user interface capability, but access to internal control system data remains difficult and under the control of vendors.

Modular open architectures require that the system be incrementally adaptable to changing requirements. Consider the needs for CNC applications listed in Table 2. Users can do some of these things on the PC front end, but many others require modifying the control system by adding 1/0 modules, using different loop closure algorithms, or enhancing logic control functions.

Many of these enhancements prove very difficult or impossible to implement on proprietary control systems. If we also consider the requirements of process applications and discrete logic applications, the list of enhancements or changes will grow. Once again, the PC front end can only address part of the needs.

Will the new open architecture make control packages now in use obsolete? Must all software written for proprietary systems be replaced?

Many proprietary control packages will become obsolete because of advances in hardware and software technologies. And yes, users will need to replace or modify many control packages so that they have standard interface "wrappers" around them. These wrappers will permit control package integration with control components that conform to the open standard interfaces.