Open, Modular Architecture Controls at GM Powertrain -- Executive Summary


Authors :

C. Michael Taylor
director, GM Powertrain Manufacturing Engineering Controls Council


Thomas J. Yager
controls manager, manufacturing engineering - engines

Raymond P. Caille
controls manager, manufacturing engineering - transmissions

Stephen R. Walker
controls manager, manufacturing engineering - castings

C. Jerry Yen
manager, advanced controls

Clark P. Bailo
manager, math-based design and systems controls

General Motors Powertrain Group (GMPTG) has been the leader in implementing open, modular architecture controller (OMAC) technologies in its manufacturing applications since 1986. The interest in OMAC has been greatly expanded for the past two years because of the advancement of personal computer technologies and the publishing of the OMAC white paper by the U.S. automotive companies stating the requirements of OMAC technologies in automotive applications. The purpose of this document is to describe the current OMAC projects and future direction of implementation at GMPTG in order to satisfy the desire from the controls community to have a better understanding of GMPTG's activities related to OMAC.

An overview of the OMAC project and the definition of the OMAC concept are described first. The rationale of pursuing open technologies is explained from the perspective of GMPTG in lieu of its organizational background and agile manufacturing strategy. Examples of existing PC-based control applications are listed to demonstrate the extensive commitment to PC-based technologies that has already been put in place. A migration plan from PC-based to OMAC-based systems with the thorough approach of validation are presented next to convey the direction that GMPTG is taking in implementing OMAC technologies.

Leveraged technology development projects and corresponding GMPTG OMAC pilot implementations are described to illustrate the philosophy and approaches toward the development of OMAC technologies at GMPTG. Finally, technical and non-technical issues are discussed next to highlight efforts that are still required to have successful implementations of OMAC systems.


Historically, divisions that are now parts of GM Powertrain Group (GMPT) have been considered to be leaders and innovators in the field of industrial control. The basic architecture of a Programmable Logic Controller (PLC) was described by a group of GM engineers in the early sixties. The Hydra-matic Ypsilanti facility became the birthplace of the PLC by implementing the first systems that later became the foundation of Modicon's and Allen-Bradley's PLC business. Being the largest manufacturer of engines, transmissions and castings in the world give GMPTG the unique opportunity to remain as a leader in the industrial controls field and to also receive the greatest benefit by improvements in this area. Other computer industries have shown that there is a tremendous advantage to having open, modular computing systems to improve system reliability and reduce costs by creating intense competition for each and every component in a computing system. This understanding of other industries has driven GMPTG to create, promote, implement and support the open, modular architecture controls (OMAC) concept. Early efforts by the U.S. government to establish open architecture controllers met with limited success. Because of this limited success, many new government sponsored programs were started to continue where the Next Generation Controller (NGC) project left off. GM had followed the NGC program very closely and wanted to ensure that these new government programs had a consistent set of requirements from the automotive industry regarding the OMAC. Therefore, these requirements were reduced to a high level white paper.

A great deal of interest in the OMAC technologies has been generated ever since the original OMAC white paper, entitled 'Requirements of Open, Modular Architecture Controllers for Applications in the Automotive Industry, Version 1.0' dated August 15, 1994, was published by the U.S. automotive companies. GM personnel have had meetings with many controls suppliers, end users, technology developers, original equipment manufacturers, and system integrators to explain the vision and strategy of control system implementation at GMPTG and discuss issues relating to the development and implementation of OMAC technologies. A partial list of conferences, groups, and companies that these concepts have been presented before is as follows:


Autofact '94, ISA Toronto, ISA New Orleans, IPC '95 TEAM Albuquerque, Japan Open Controls Conference, ICEE 96

End Users:

GM Powertrain, Adam Opel, Ford, Chrysler, Toyota, Nissan, GM NAO-MIS

Controls Suppliers:

Allen-Bradley, GE Fanuc, Square D, Modicon, NUM, Indramat, Siemens, ICON Shreveport, Delta Tau, Cimetrix, Fanuc, ASAP, Honeywell Microswitch, Steeplechase, Trellis, Controlware

Machine Tool Builders:

Landis, Okuma, Makino, Leblond Makino, Cincinnati Milacron, Mori Seki, Mazak, Huller Hille, Boehringer, Toyoda, Lamb Technicon

Computer Manufacturers:

Hewlett-Packard, Intel, Digital Equipment, Nematron, Xycom, Radisys

System Integrators:


Other Organizations:

National Electrical Manufacturers Association (NEMA), National Institute of Standards and Technology (NIST), European Open System Architecture for Controls within Automation Systems (OSACA), Japan International Robotics and Factory Automation (IROFA), Japan Open System Environment for Controller Architecture (OSEC),

This document is intended to be a complementary document to the OMAC white paper. It captures many technology and implementation issues related to OMAC, in general and specific to GMPTG. It also contains the approaches that GMPTG personnel are taking to evaluate and validate OMAC technologies and also the procedures to transfer OMAC technologies to the production floor. In an effort to convey this information more readily, excerpts from these presentations have been reduced to writing such that many more people and groups can understand the concepts being offered by the OMAC document.

The objectives of this document are summarized as follows:

  • to communicate GMPTG's viewpoints and thoughts regarding OMAC to the controls community;

  • to clarify GMPTG's position in the implementation of OMAC-based systems;

  • to help accelerate the availability of commercial OMAC products;

  • to address concerns from control vendors, machine tool suppliers, and system integrators.

It must be emphasized that this document is neither a specification for equipment procurement nor a design document telling control suppliers how to design their products.

Description of the OMAC Project

The question, ' What is the OMAC project?' was asked by many people looking for a structured, well defined program that they can refer to. The best answer to the question, from the GM Powertrain perspective, is that OMAC is a collection of development and implementation activities that are NOT connected through a formal organization but rather through cooperative information exchanges and joint development efforts by a group of organizations driven by the common goal of making control systems more open and modular. In other words, there are no OMAC headquarters, no elected officers, and no official charters in the so called OMAC project.

The OMAC effort was initiated by automotive companies in the U.S. to satisfy their desires to make their manufacturing systems more flexible and agile, and encourage control suppliers to commercialize open, modular control products. The OMAC White paper was published to describe specific needs and requirements in automotive manufacturing applications, define 'open' and 'modular' in the context of automotive manufacturing requirements, describe the basic controller modules and modularity concept, and define high level functional requirements for each controller module. It was intended to be a communication tool from the automotive companies and make known the 'wish list' of features that are needed in an open, modular control system. For GMPTG, the OMAC White paper is used to inform the controls vendors and technology providers the direction that GMPTG is heading and some of the technologies that should be incorporated to help GMPTG achieve the goal of implementing flexible, cost competitive manufacturing processes. GMPTG is moving away from closed, proprietary control systems that have to be scrapped when changes or upgrades are required. Having control systems that are open and modular will enable new technologies to be integrated in an incremental manner.

Therefore, the OMAC White paper is NOT a set of technical specifications and should not be considered as a set of rules to 'tell' vendors how to design control systems. It is also neither the intention of the OMAC White paper to dictate the architecture of an open, modular control system, nor does it try to achieve consensus from the vendor community on the architecture of an OMAC system. Thus, no technical specifications and OMAC architecture will be published by the 'OMAC project.' Technical specifications will be published by the development projects co-sponsored by the U.S. government, and cooperative development efforts among these projects will result in a common set of specifications. The ultimate goal of the 'OMAC project' is for the automotive companies to purchase commercially available control products that meet this set of common specifications.

Having a common, open controller platform will benefit not only automotive companies but also any business requiring industrial control. The competitive advantage an individual company can achieve is by easy incorporation of its own proprietary engineering knowledge in the controllers, resulting in more flexible, more capable manufacturing processes. Current proprietary control systems make the integration of in-house technologies very difficult. Another important element of the OMAC project is to leverage the rapid technology advancement and large volume of sales in the personal computer hardware and software markets. The majority of the applications in the automotive industry are 'low-end' applications which do not require complicated control systems and can be served by off-the-shelf products based on personal computer hardware and software. Elements such as a graphical user interface, hardware platform, operating system and operating environment, communication, I/O network, programming language, etc. should not have to be re-invented to meet OMAC requirements. GMPTG believes that having an open, modular controller presents a better opportunity for vendors with specialty products to become more significant players in automotive applications. Control vendors are encouraged to work with personnel from GMPTG to develop products that can be easily and widely applied by many users, but it should be emphasized that the OMAC project is a cooperative effort and no vendors should feel like they are being forced to participate in the OMAC activities.

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