Robert G. Landers (landersr@mst.edu, 573–341–4586), Levent Acar, S.N. Balakrishnan, Mike Hilgers, Ming Leu, Frank Liou, Bruce McMillin, Tony Okafor, Can Saygin, Matt Goska, and Yan Tang

Parallel machine tools utilize multiple tools simultaneously, but independently, on a single part. Thus, these machine tools offer the benefits of increased productivity due to multiple operations being performed simultaneously, increased quality due to a reduction in the number of setups, and decreased floor space. Further, their flexibility will make parallel machine tools a key component in future reconfigurable manufacturing enterprises. This project seeks to develop a parallel machine tool for research and education in advanced manufacturing. The parallel machine tool will have the capability to perform parallel milling and drilling operations on both cylindrical and prismatic parts, as well as parallel lathing operations on cylindrical parts. The developed parallel machine tool will have an open control system providing for the ability to easily reconfigure the software structure and the monitoring, control, and diagnostic modules. The open control platform will provide the means to implement process planning and control laboratories in advanced manufacturing automation courses. One research project currently being conducted will create a systematic controller design methodology for manufacturing equipment using hierarchical control techniques. In this methodology, the operation and process requirements will be propagated to the servomechanism level and the controllers at this level will be directly designed such that these operation requirements, in addition to the servomechanism tracking requirements, are satisfied.

1. “Hierarchical Optimal Control of Two–Axis Motion Systems,�? B. Pandurangan, R. G. Landers, and S. N. Balakrishnan, 2004, American Control Conference, Boston, Massachusetts, June 30–July 2 (submitted).

Abstract: Complex motion control systems are critical in many applications (e.g., manufacturing, robotics). Often a contour controller, in addition to individual servomechanism controllers, is implemented to drive the contour error (i.e., deviation between the actual position and the contour) to zero by sending off–set control signals to the individual servomechanisms. The contour controller, though, adds significant complexity to the overall control system. In this paper a contour controller based on optimal hierarchical techniques is proposed. The overall control objective (i.e., zero contour error) is propagated to the servomechanism level via an aggregation relationship between the contour error and the physical servomechanism variables. A controller is designed, via optimal control techniques, at the servomechanism level that simultaneously meet the overall control objective and the local control objectives (i.e., individual axis tracking). Simulations results for diamond and circular contours demonstrate the excellent tracking ability of the proposed motion control methodology.

2. “Hierarchical Optimal Control of a Turning Process – Linearization Approach,�? A. Dasgupta, B. Pandurangan, R. G. Landers, and S. N. Balakrishnan, 2003, American Control Conference, Denver, Colorado, June 4–6, pp. 2606–2613.

Abstract: In this paper a hierarchical controller is developed to regulate the machining forces such that the productivity is maximized. The overall control objective is stated in terms of how the cutting force should be regulated. The upper level controller regulates the cutting forces directly and generates the transient performance of the force trajectory i.e., the upper level goals. The goals are then propagated to the lower level. The lower level controller tracks the goals of the upper level and decides on the trajectories of the feed and position so as to implement the force trajectory of the upper level. Using the proposed method, only a simulated force trajectory is required to control the feed. The feed in turn controls the cutting force. Thus, simultaneous control of the force–feed trajectories is possible. Simulations are conducted to validate the developed methodology.

3. “Output Feedback Force Control for a Parallel Turning Operation,�? R. Sudhakara, and R. G. Landers, 2003, American Control Conference, Denver, Colorado, June 4–6, pp. 2596–2601.

Abstract: Parallel machine tools (i.e., machine tools capable of cutting a part with multiple tools simultaneously but independently) are being utilized more and more to increase operation productivity, decrease setups, and reduce floor space. Process control is the utilization of real–time process sensor information to automatically adjust process parameters (e.g., feed, spindle speed) to increase operation productivity and quality. To date, however these two technologies have not been combined. This paper describes the design of an output feedback controller for a parallel turning operation that accounts for the inherent nonlinearities in the force process. An analysis of the process equilibriums explains the system stability behavior for different design specifications and the reverse trajectory method is used to numerically determine the exact stability boundary. Effects of saturation on stability are also analyzed and from this sufficient conditions for global stability are obtained.