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Original Date: 01/27/1997
Revision Date: 01/18/2007
Best Practice : Electronic Technologies for Precision Manufacturing
Lawrence Livermore National Laboratory (LLNL) has a long history of expertise in precision machining and inspection gauges. Since the early 1980s, the laboratory has been developing and building advanced computer control systems for a variety of applications. In most cases, it was necessary for LLNL to develop controllers because there was nothing available in the commercial sector to meet the specific application requirements. Applications included digital signal processing for scanning types of coordinate measuring machines; multi-loop servo systems for precision applications; sensors and electronics for high precision measurements and positioning; remote machining of explosives and other energetic materials; and inexpensive temperature control.
Currently, LLNL has a major effort underway to develop a next generation controller for manufacturing. It is in response to needs in the Department of Energy (DOE) and the commercial sector for more flexibility and maintainability in controllers. The project is a joint effort led by LLNL involving other DOE facilities and industry partners. Present emphasis of the project is to look at the total manufacturing system (Figure 2-2) and develop a machine controller with the following capabilities:
Input process model information and process unique control strategies into the manufacturing controls software
Rapidly communicate between controllers over a network so that controllers can be coordinated and integrated
Handle in-process monitoring of critical process parameters, real-time calculation of control algorithm changes based on in-process measurements, and reporting of process variations to quality assurance
Intelligently deal with exception handling in a complex manufacturing environment
Many of the design constraints are influenced by the industry partners who require the system to use commercially- available hardware. It must run on Intel architecture PCS in real time using familiar tools such as Windows 95. LLNL is serving as an independent broker to assure that commercially available and standardized components are selected to provide the hardware design baseline for the system software.
LLNL is developing the Manufacturing Operating System (MOS) software that will create an environment that allows the largest variety of control problems to be solved over a wide range of performance and cost constraints. This system will allow the existing sequential nature of manufacturing to be replaced by a more agile process. Improvement goals are to develop a software system capable of executing motion control functions at the CPU level on a PC, and to interface with a variety of commercially-available sensor and actuator systems via commercially- available interfaces. The key to this architecture is the ability of users to reconfigure the controller for their process. The MOS enables users to quickly reconfigure machine tools to produce different parts on demand by simply changing software. When unanticipated tasks arise, hardware redesign will be unnecessary.
LLNL is designing Application Programming Interfaces (APIs) that allow the MOS to be reconfigured for unanticipated tasks. APIs enable users to concentrate on specific manufacturing process problems rather than having to build entire controllers from the ground up. This approach supports functions migrating either to or from hardware-based accelerators depending on cost and performance constraints. This approach is so promising that NIST has agreed to develop standards for APIs.
These APIs, depicted in Figure 2-3, divide the controller into well-defined modules. These correspond with known functions in current controllers, and will also provide extended and improved services in future controllers. For producing a particular product, one module might direct the trajectory of a machine tool, one could solve logic problems, and another could coordinate tasks. Application modules can be specific to a milling machine, lathe, or almost any other manufacturing step. New functions or specialized modules could be added simply by plugging them in.
A proof-of-concept prototype is running at an industrial site. It controls a K&T 3-axis milling machine. The system is totally software based. It uses a single PC processor and SERCOS standard as the motor drive interface. The core of the controller is the industrial partner’s existing human interface software combined with LLNL’s existing motion control software.
Figure 2-2. Advanced Controller Within the Total Manufacturing System
Figure 2-3. MOS Architecture
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