Foundational Research On Open Architecture CNC Systems

Nowadays, open architecture CNC systems are becoming one of the most important directions of CNC technology. The research purpose of open CNC system is to build a modular, reconfigurable and expandable architecture of CNC systems to improve the system's flexibility, and enable the systems to be re-developed. As a result, CNC systems can be responsive to the market quickly and economically.With the development of international open CNC projects, more attention is paid to open CNC at home. But relative researches are still at the stage of beginning and are non-systematical. In this thesis, some key aspects and technology on the design of open architecture CNC systems are researched, including system architecture analysis, open hardware structure design, software modeling and developing, curve interpolation technology in motion control, etc. Following are the main work and results:(1) For concept design, some basic aspects about open CNC systems are investigated, including the importance of architecture to CNC system capabilities and development, the features and drawbacks of current architecture, and why and how for CNC systems to be open. Some principles and a concept model for open architecture systems are proposed which can be used as the guidance of detailed design of the software and hardware.(2) To meet the requirements of open characteristics of CNC systems, the design principles of open system hardware are investigated. Based on the bus selection and the division of system hardware, a distributed modular CNC system hardware structure with field-bus is proposed. Design methods of the modular system and its function modules based on CAN-bus are presented in detail.(3) The software architecture of open CNC systems are studied and the software developing method applying COM technology is proposed. Object-oriented analysis and behavior-based modeling are used respectively for the modeling of software's static functions and dynamic behaviors, and a multi-lay modular software structure is suggested. Furthermore, the software's developing technology based on COM components is presented.(4) Curve interpolators of open CNC are systematically studied, and some new interpolation algorithms are proposed, which can greatly improve the capability of track controlling in CNC system's, simplify NC programming, and may result in a common curve expression in CAD/CAM/CNC. The machining precision and efficiency can be greatly improved by use of the curve interpolators, which is a key for modern highperformance CNC systems.(5) NURBS curves interpolation for high speed and high precision machining is systematically studied, and a real-time interpolator for NURBS curves in CNC systems is proposed. As a NURBS curve is expressed with a subsection parameterized rational equation, the calculation of its track, derivative and curvature is very complicated. The proposed interpolator generates NURBS curves based on parameter predicting and correcting. The calculation in real-time is significantly simplified by the preprocessing, avoiding the derivation of curves, and approximating the radius of curvature. This provides the NURBS curves interpolator with good real-time performance.(6) In order to meet the requirements of high-speed and high-accuracy machining, performance control in curve interpolators is studied and a new method is presented. Comparing with the traditional static-control, the proposed method supervises tolerances in various concerned factors in real-time, and adapts feed-rate with the curve's curvature to limit the contour errors and feed-acceleration within the allowable ranges in order that curve interpolators can satisfy the controlling demand for high-speed and high-precision of modem CNC machine tools.