UC Davis
UC Davis Previously Published Works
Title
An intelligent NC program processor for CNC system of machine tool
Permalink
https://escholarship.org/uc/item/65r5c7tj
Journal
Robotics and Computer-Integrated Manufacturing, 23(2)
ISSN
0736-5845
Authors
Liu, Y
Guo, X
Li, W
et al.
Publication Date
2007-04-01
Peer reviewed
eScholarship.org Powered by the California Digital Library
University of California
1
An Intelligent NC Program Processor for CNC System of Machine Tool
Yadong Liu
1
, Xingui Guo
1
, Wei Li
1
, Kazuo Yamazaki
1
, Keizo Kashihara
2
, Makoto Fujishima
2
1
IMS-Mechatronics Laboratory, Mechanical Aeronautical Engineering Department, University of
California, Davis, USA
2
Mori Seiki Co. Ltd., 2-35-16 Meieki, Nakamura-ku, Nagoya City, Japan
Abstract
NC program interpreting is one of the most important tasks of CNC in machine tool system. The
existing CNC systems only support vendor-specific NC program input, which restrict the applying
of other similar functional NC programs with different program format. Especially for those users
owning several machine tools with different CNC from the same provider, the diversity of NC
programs dramatically increases their cost and time on operator training and machine tool
maintenance. In order to deal with the variety of NC program, an intelligent NC program
processor (NCPP) is proposed in this paper. The proposed NCPP has a novel structure with
separated NC specification dictionary and processing engine, which ease the CNC system to
adapt to a new NC program specification by only updating the NC specification dictionary (NCSD).
This paper explains the NC specification dictionary structure by using EBNF representation,
which is further implemented in TCL, an embedded script language tool. Meanwhile, the
unchanged processing engine has been designed from a compiler’s point of view to process the
data dictionary. A NCPP prototype is built to evaluate the proposed design. Case study shows
that the proposed NCPP handles different NC program inputs successfully.
Keywords: NC Program Processor, Canonical Machining Function, EBNF, TCL
1 INTRODUCTION
In the CNC system of modern machine tool, NC program interpreting is very important, which is in
charge of the accurate resolving of machining intention generated from CAM system. Figure 1
shows the role of NC program processor (NCPP) in CNC system, the input is NC program. The
major function of NCPP is to decode the input into motion command and PLC command, and
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send them to the motion control processor (MCP) and programmable logic controller (PLC) of
CNC separately in order to control the movement of the cutting tool and auxiliary machine logic.
Most CNC systems can handle only one specific NC program format, while the diversity of NC
programs always entangles the machine tool users, especially for those owning several machine
tools with different CNC but from the same provider. Such a situation is formed due to the
following facts:
First, no actual NC program standard is available, although some nominal ones are existing.
There have been three basic standards: RS274D (USA), ISO6983 (ISO) and DIN66025 (Europe)
for NC program since CNC was invented. However, machine tool and control technology have
undergone great development since then, thus a lot of new functions and controller-specific
features, not supported by these NC standards have been added to the CNC.
Second, different CNC providers extended the NC program standard a lot to adapt their own
specific functions; a typical example is the special interpolation function added by each CNC
provider. This contributes to the difficulty of interchanging NC programs generated by different
CNC systems. Hence, even the users who own several kinds of machine tools from the same
machine tool manufacturer but equipped with different CNC systems have to generate different
NC programs for each machine tool. This situation even happens in the same CNC system case
with later updated functions.
Third, NC program modification is always mandatory in order to safely reuse a NC program with
different format. This process usually requires much more specialist knowledge of different kinds
of CNC, although the CNC providers always say that only less than 5% change is needed. This
issue obviously forces the machine tool users to spend more expense and time on training their
programmers or operators.
Fourth, most CAM system can generate different NC program by applying different post-processor
now. However, it’s not workable for manual programming cases, which still cover major
applications in industry. In addition, different CNC system requires different post-processor, the
CAM system thus has to prepare a lot of unused post-processors in advance. Universal post-
3
processor is another solution, which allows the end user to customize a post-processor; however
making a specific post-processor requires much more experienced specialists.
In order to efficiently reuse NC programs from different CNC systems, an intelligent NCPP is
proposed to deal with variety of NC program inputs in CNC system. With separated processing
engine and NC specification dictionary (NCSD) structure, the proposed NCPP can easily interpret
different NC programs by applying different specification dictionaries while keeping the processing
engine unchanged.
The rest portions of this paper are organized as following. In Section 2, the interface of NCPP is
introduced. In Section 3, conceptual model of proposed NCPP is presented. Section 4 discusses
the design of proposed NCPP. Section 5 shows the implementation of a prototype system. The
paper is concluded in Section 6.
2 INTERFACE OF NC PROGRAM PROCESSOR
NCPP is one module of the CNC, which requires cooperation between different modules;
therefore it’s quite necessary to clarify the interface before starting design. As shown in Figure 1,
the purpose of NCPP is to translate the input NC program into machine instruction, such as
motion command, PLC command or simple parameter settings and error messages. NIST calls
these outputs as Canonical Machining Functions. A set of definition of these canonical machining
functions has been given as shown in table 1, which has been used by Enhanced Machine
Controller (EMC) project and other open CNC research projects.
NC program
in memory
Manual Data
Input (MDI)
Motion
command
PLC
command
NC program
from DNC
INPUT OUTPUT
Motion
command
&PLC
command
distributor
Parameter
setting
Error
message
NC
Program
Processor
(NCPP)
MCP
PLC
Figure 1: Role of NCPP in CNC system.
The canonical machining functions were devised with two objectives in mind:
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• All the functionality of common 3-axis to 5-axis machining centers had to be covered by the
functions; for any function a machining center can perform, there has to be a way to tell it to do
that function.
• It must be possible to interpret RS274-compatible NC program into canonical machining function
calls.
Table 1: Canonical machining function definitions.
Functionality Functions
Representation
SET_ORIGIN_OFFSETS(x,y,z,a,b,c)
USE_LENGTH_UNITS(units)
Free Space Motion STRAIGHT_TRAVERSE(x,y,z,a,b,c)
Machining Attributes
SELECT_PLANE(plane)
SET_FEED_RATE(rate)
SET_MOTION_CONTROL_MODE(mode)
……
Machining Functions
ARC_FEED(first_end, second_end, …)
DWELL (seconds)
STRAIGHT_FEED(x,y,z,a,b,c)
Spindle Functions
SET_SPINDLE_SPEED(r)
START_SPINDLE_CLOCKWISE()
STOP_SPINDLE_TURNING()
Tool Functions
CHANGE_TOOL(slot)
SELECT_TOOL(i)
…… ……
The canonical machining functions are atomic commands. Each function produces a single tool
motion or a single logical action. A NC command usually includes two types: those for which a
single NC command corresponds exactly to a canonical function call and those for which a single
command will be decomposed into several canonical function calls. Things like “move in a straight
