A Next Generation NC Machining System Based on NC Feature Unit and Real-Time Tool-Path Generation
1. Introduction
In the past 50 years, in the field of numerical control technology,
great progress has been made in hardware and software,
in terms of function, speed, precision, and reliability. However,
Correspondence and offprint requests to: L. Zhang, The Hong Kong
Polytechnic University, Department of Computing, Hung Hom,
Kowloon, Hong Kong. E-mail: cslzhangKcomp.polyu.edu.hk
from the viewpoint of automatic control, in modern NC machining
systems, the traditional control mode still remains, in
which tool-path generation and tool-path control are performed
separately by two independent systems: a numerical control
programming (NCP) system and a computer numerical control
(CNC) system. The process of traditional NC machining is
divided into two steps. The first step is to generate tool paths
in the NCP system in an off-line mode. Its output is the Gcode
program. The second step is executed in a CNC system
in real-time mode. Its purpose is to control the actual cutting
processes according to fixed G-code programs. Only two parameters
can be modified during the real-time control process:
feedrate and spindle speed. In other words, up to now, a
traditional NC machining system still uses an open-loop control
mode. The main reason for this is that the tool-path calculation
process is too time-consuming to be completed in real-time.
Also, because of the complexity and diversity of machined
parts, it is impossible to integrate all the functions into one
control system to meet the demand of the various NC machining
actions.