New Commerce Department Collaborative Facility Focuses On Emerging "Parallel" Machine Tools

A new manufacturing-research facility aimed at refining and extending the raw capabilities of an emerging and potentially revolutionary class of prism-shaped machine tools has opened its doors at the Commerce Department's National Institute of Standards and Technology in Gaithersburg, Md.

Promising an unprecedented combination of versatility, stiffness, speed and accuracy, the geometric oddity at the center of NIST's new National Advanced Manufacturing Testbed exemplifies the first major departure in machine tool design in nearly a century. Several U.S. and foreign machine tool makers are pursuing variations on the same geometric theme, while prospective customers are beginning to contemplate what the novel technology might mean for their manufacturing operations.

Among domestic manufacturers eager to explore those possibilities, Pratt & Whitney, the Connecticut-based maker of aircraft engines, is the first to join with NIST manufacturing researchers to study the unique capabilities of the new, so-called "parallel" machine tools. Other U.S. companies and several universities are exploring cooperative research opportunities at the testbed.

"This is an opportunity for us to find out what the technology can do," explains Joseph D. Drescher, P&W; senior precision manufacturing engineer. "We need good generic data to judge whether there are significant advantages to be realized in our operations. The collaboration reduces the size of the gamble we must take to learn about the capabilities first hand."

Since June, NIST scientists and engineers have been benchmarking the capabilities of an "octahedral hexapod." Built by the Ingersoll Milling Machine Co., the hexapod is representative of the small, but growing class of parallel machine tools. (See attached supplement "Research Seeks Structural Advantage in Parallel Machine Tools" for a description.) After initial characterization of the novel technology, the research focus will expand to techniques and standards for enhancing the performance of parallel machines in a variety of precision manufacturing applications.

As expected during the early stages of any new technology, it is unclear just how well parallel machines stack up against conventional machine tools. "Right now, we and our partners are trying to find out what this technology is all about to learn about its attributes and its limitations," explains Fred Rudder, a NIST precision engineering researcher and co-manager of the hexapod project. "This research and evaluation is part of a sorting-out process. Industry needs answers before it can assess whether parallel machines offer the opportunity for leapfrog advances in specific applications."

To help manufacturers assess the utility of parallel machines, NIST will work with companies and private standards organizations to develop common performance- evaluation methods. Standardized procedures for characterizing the performance of conventional machine tools have been developed, but these methods do not apply to parallel machines.

"The accuracy and overall performance of conventional machine tools depends, to a great degree, on how precisely the guideways and other mechanical elements are machined and assembled," says NIST robotics researcher Albert Wavering, the other project manager. "For hexapods and other parallel machines, accuracy depends mostly on the control and coordination of the strut movements. Parallel machines are much more computer intensive, which, we think, will prove to be an advantage. It should be much easier to change software instructions to improve performance and correct errors than it is to change the mechanical components of the machine."

As they develop the technical basis for standardized performance methods, researchers also will evaluate the potential of parallel machines to simplify existing machining processes. That potential lies in the collection of capabilities that the technology offers, rather than any single proficiency, such as cutting speed or accuracy. "The challenge," Rudder says, "is to determine what this unique combination of characteristics enables manufacturers to do and to do better."

Parallel machines have emerged at a pivotal stage in the evolution of manufacturing, Rudder suggests. Studies indicate that dimensional tolerances have been decreasing fourfold to tenfold each decade. By the year 2000, tolerances for pistons and other car-engine parts, for example, will be pared to 1 micrometer, a tiny fraction of the width of a human hair. Consistently achieving such demanding tolerances now requires highly specialized machines operating under highly controlled environmental conditions requirements that add significantly to manufacturing costs.

If the potential capabilities of parallel machines are realized, according to Rudder, manufacturers should find it easier to keep pace with the trend toward ever-smaller tolerances and ever-more complicated part geometries. An aim of the hexapod project is to develop the underlying measurement methods and technology needed to achieve high levels of positioning accuracy and resolution. Researchers will incorporate microactuators into the hexapod so that strut lengths can be changed in precise micrometer-scale increments. They also intend to develop an on-machine metrology system for measuring strut lengths to a targeted accuracy of 1 micrometer. Eventually, the NIST team plans to develop a system for self-calibration, so that machines can check their own performance and correct any detected inaccuracies.

A chief goal of manufacturers is increased agility the ability to respond quickly to changing market demands and new opportunities. Here too, parallel machines may play an instrumental role. Wavering points out, for example, that the machines are essentially portable, allowing manufacturers to rearrange the factory floor to achieve the optimal layout for a particular set of processes. And because of their multipurpose capabilities, parallel machines could help to eliminate production bottlenecks by reducing the need for dedicated machines designed to perform one or, at best, a few highly specific tasks.

In addition, Wavering and Rudder note that the machines appear to be well suited for contouring large surfaces and for machining dies for precision sheet-metal forming. That could speed development of dies and molds now a costly and lengthy process that adds significantly to the time it takes to bring new car models and other products to market.

To help NIST and its partners probe and push the performance envelope of the new technology, Wavering's team will install a NIST-developed enhanced machine tool controller, or EMC, on the hexapod. Developed by a team led by NIST robotics researcher Frederick Proctor, the EMC features an open architecture, which simplifies the task of making performance-enhancing modifications embodied either in software or hardware. The research controller is now undergoing testing at a General Motors factory. With the controller's standardized, "plug and play" interfaces, developing, installing and integrating experimental features and applications should be straightforward, unlike the often tortuous, one-of-a-kind programming efforts required to modify the proprietary controllers now used with most machine tools.

The new parallel machine facility also will serve as a node in NIST's National Advanced Manufacturing Testbed. Devoted to virtual and distributed manufacturing, the NAMT is slated to get under way during the 1996 fiscal year. Research will focus largely on developing and demonstrating prototype standards for simulating production processes and for enabling geographically dispersed manufacturing systems to work together and to quickly incorporate new technologies.

The hexapod machine will be used as a proving ground for real-time approaches to simulating and modeling manufacturing processes. In addition, data from hexapod-based research will be electronically available to remotely located collaborators, who also will be able to transmit part designs and application programs to the testbed.

Through the NAMT, access to the experimental machine tool will be greatly expanded, providing researchers at companies and universities with the opportunity to gain experience with an important emerging manufacturing technology.

As a non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and apply technology, measurements and standards.