Recently, various customers’ demands in response to rapidly changing market environments, and new process technologies have driven the trend toward new paradigms in manufacturing systems such as RMS (Reconfigurable Manufacturing System), in addition to traditional FMS and CIM. These conditions have also prompted the open architecture controller (OAC), which permits the flexibility, expandability and integrability.
It has been reported that OAC allows modular integration of software applications and hardware equipments developed by various vendors under a standard platform. Researchers have focused on developing an open architecture control system that requires its control environment to conform to an open technology, not to force all manufacturing vendors to conform to one standard. This characteristic makes it feasible to reconfigure existing control resources and user-specific functions, and adjust the manufacturing system capacity according to market demands immediately. Under the open architecture control scheme, standard functions of CNC machine tools have hardware independent modular architecture, which allows integrating user-specific functions such as real-time compensations and high-level control strategies with standard function modules feasibly.
Recently, challenges for relating geometric representations in CAD to manufacturing oriented information in CNC have been made. The open architecture CNC system must be able to adapt new techniques for designing free-form shapes in CAD/CAM systems, and an intelligent capability that changes the trajectory in real-time dynamically from information gathered by sensors or predictive compensations. Among those efforts, the “parametric interpolator” is one that currently attracts a lot of attention. The parametric interpolator generates a curved cutter path directly without segmentation contours processing, which causes feedrate discontinuities among NC blocks, resulting in the high tracking accuracy and machining efficiency.
However, it is difficult to blend these new approaches with existing CNC environments, because the interpolator modules, usually provided as API or macro allow only to process NC blocks separately, not to expand or combine existing interpolation resources flexibly, even in open architecture control systems. Concerning with the smooth trajectory generation encompassing a sequence of various NC blocks, the design of interpolator generalized for every NC block is important. Flexible interpolator environments are also required for integrating various interpolation techniques with the existing resources easily.
This paper presents the design and implementation of object-oriented interpreter/interpolator modules and a PC based open architecture CNC system, which permits these modules. The object-oriented modeling technology provides inheritance and polymorphism for code to be more reusable. It is possible to design a new user-specific interpolator by using trajectory block objects which have abstracted interfaces and designing subdivided modules commonly applicable to each block object, such as acceleration/deceleration module and ‘look-ahead’ function for the geometric intelligence. It is also feasible to add the support for new curve/surface blocks, not a simple combination of existing NC blocks, to the existing interpolator resources, resulting in the smooth feedrate profile generation encompassing a sequence of mixed NC blocks.
