Open, Modular Architecture Controls at GM Powertrain — Migration Plan

By C. Michael Taylor, et al. January 27, 1998
Validation Process
he current implementation of PC-based control systems is strictly in discrete logic control applications. The OMAC concept certainly is not limited to discrete control systems only. GMPTG is taking steps to migrate the OMAC direction into CNC and robotics control systems.

Table 2 gives an overview of the control migration plan for GMPTG by application types. ‘Current’ applications are the ones already implemented or are in the process of being implemented in the plants. ‘Near Future’ applications are the ones that GMPTG is in the process of procuring equipment for programs starting in 1997 and 1998. The timing of ‘Future’ applications is not firm, but will be for programs in the 1998 time frame and beyond.

Current PV6/L850 Future
PC Controls PC Controls OMAC Controls
Assembly Lines PC Controls PC Controls OMAC Controls
Agile CNC Machining Lines Tier II CNC & PC Controls (Material Handling) Tier II CNC (PC Front End) & PC Controls (Material Handling) OMAC Controls
Stand-Alone non-CNC Machining Systems PLC or PC Controls PLC or PC Controls OMAC Controls
Stand-Alone CNC Machining Systems Tier II CNC or OEM CNC Tier II, OEM CNC (PC Front End) or Open PC Controls OMAC Controls
Stand-Alone Casting Systems PLC PLC or PC Controls OMAC Controls
Integrated Cell Casting Systems PLC PLC or PC Controls OMAC Controls

Table 2. GMPTG Control Migration Plan

Current ‘Transfer Line’ and ‘Assembly Line’ applications are based on FloPror control systems as stated in the previous section. Some of these applications also include integrated motion using Genius. Proprietary CNC controllers are being used in current machining applications. ‘Agile CNC Machining Lines’ employ proprietary CNC controllers from ‘Tier Two’ suppliers such as GE Fanuc but utilize PC based control systems for material handling. Standalone CNC machines have controllers from either ‘Tier Two’ suppliers or proprietary controllers from machine tool builders. Standalone non-CNC machines have simpler control requirements, and many of them employ small PLC’s as their controllers, and in some cases, PC-based control systems have already been implemented.

Figure 7. GMPTG Validation Process

Two significant changes for the Premium V6 and L850 engine programs that are currently being implemented are the requirements: (1) to have a PC front end for each proprietary CNC controller, and (2) to use SERCOS as the standard interface between a controller and drives. The PC front end requirement is to satisfy the strategy of having a common look and feel user interface that was outlined earlier. The SERCOS requirement is one step toward defining standard interfaces in all control systems. Some of the applications in these programs include integrated motion on Interbus-S with Indramat drives.

Highlights of the current GMPTG CNC specifications include:

  • basis of the user interface shall be a personal computer;

  • user interface subsystem must be customizable by end user;

  • operating system of the user interface shall be Windows 3.1, Windows 95, OS/2, or Windows NT;

  • logic control shall be done in IEC-1131 compliant ladder logic or in flowchart programming;

  • logic control programs and part programs shall be editable by GMPTG controls personnel;

  • interface to drives shall be SERCOS.

GMPTG is taking incremental steps toward implementing OMAC-based CNC control systems because GMPTG engineers are not convinced that commercially available open, modular CNC controllers have been thoroughly validated and proven to be reliable for full scale plant deployment at the present time. However, it is also very feasible that in another 18 to 24 months, the open, modular control systems will be validated and proven for all GMPTG control applications.

Validation Process

Figure 7 illustrates the GMPTG validation process for control products, from control components to complete controllers, that are new for GMPTG applications. The main objective of executing the validation process is to minimize problems on the factory floor after control products are deployed. The main aim of the validation process is for system level validation, and suppliers are still responsible for performing their own initial product validations. The system level validation is important for integrating proprietary control products, and the importance will increase when the integration of open, modular control products from multiple suppliers becomes necessary.

The initial step of the process is for GMPTG engineers to screen the products being offered by vendors to assess their readiness in alpha, beta, or commercial stages, and whether the products meet a specific application need. The cost and availability of the products are also investigated.

If a control product passed the initial screening process, it will be evaluated and tested in a lab environment. Bench top tests are conducted to verify whether the product behaves as advertised, and engineering analysis is done to assess the true capability of the product.

After successful assessments in the lab, the control product will be integrated in a pilot system or machine for further validation. The issues that need to be validated at this stage include:

  • integration with other components in the system;

  • reliability and maintainability of the product;

  • ease of operation;

  • ability to perform real production tasks;

  • acceptance by plant floor personnel;

  • technical support from the vendor

If the control product passes the extensive pilot system testing stage, it is deemed to be ready for full deployment in a major GMPTG program. It becomes one of the validated products that can be selected for implementation in future GMPTG programs.

The time required to complete the validation process for a particular product depends on many factors such as the readiness of the product, the availability of pilot systems and/or applications, validation efforts by other organizations outside of GMPTG, deadlines for GMPTG program implementation, etc.

The validation process is not restricted to new control products only. Another aspect of this process is the integration testing for software revision, replacement components, and add-on components after the complete control system has been installed. The performance of the total integrated system is much more critical to the success of a manufacturing process.