5 axis nurbs curve interpolator using tool axis vector command
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REAL TIME 5-AXIS NURBS CURVE INTERPOLA-TOR
Sungchul Jee and Taehoon Koo
Processing Sequence CAD
Comparing with Linear interpolation Example
A CL file necessarily includes coordinates and tool orientation vec-tor in local coordinates.
▪ The proposed 5-axis NURBS interpolation format can be applied to various configuration of 5-axis machining centers without modifying the NC code.▪ The results of simulation and experiment validate the superiority of the proposed NURBS interpolator over the conventional linear interpolator.
6 control points and duplicated knots at start and end points
Geometry information
NURBS-IGES format
CAM
5-axis NURBS G-code CNC
CL file format
Interpreter (ISO-6983)
5-axis NURBS interpolator
Parser
CATIA format: x_, y_, z_, i_, j_, k_Ex) GOTO / -35.014, -65.185, 102.102, -0.416, -0.110, 0.902
HyperMill format: x[/_] y[/_] z[/_] u[/_] v[/_] w[/_]Ex) 31:oL[10](x[/10.0] y[/31.2] z[/21.3] u[/0] v[/-0.557] w[/0.830]
Vector converter
TCP control
Added a new parser rule and a vector conversion rule
Coordinate data andtool orientation vectors
The vector converter decomposes the tool orientation into two angles for rotational axes depending on machine configuration.
Interpolated data is transformed to joint axial movement by TCP(Tool Center Point) control
Objective: ▪ To propose a new 5-axis NURBS interpolator that can be easily cope with post-processing of CL files from a CAM system
▪ To evaluate and compare with the conventional linear interpolator
Rational B-spline curve entity (Type 126)Ex) 126,5,3,1,0,1,0,0.,0.,0.,0.,0.333333,0.666667,1.,1.,1.,1.,1.,1., 7P 4 1.,1.,1.,1.,-178.,109.,0.,-166.,128.,0.,-144.,109.,0.,-109., 7P 5
Machine configuration parameters
Sample codeG106 F0.9X-43 Y-43 Z0X-30.787 Y-34.290 Z9X-18.574 Y-25.581 Z9X-6.361 Y-16.872 Z-9X5.850 Y-8.163 Z-9X18.063 Y0.545 Z0I-0.569 J-0.406 K0.7I-0.429 J-0.429 K0.7I-0.347 J-0.370 K0.7I-0.381 J-0.149 K0.7I-0.299 J-0.090 K0.7I-0.158 J-0.113 K0.7R0 R0 R0 R0.25 R0.5 R0.75R1 R1 R1
TTTR
A
C
New G-code Format The proposed G-code
Independent of machine tool’s rotational axes
Format DescriptionG106 P_ ; X_ Y_ Z_ I_ J_ K_ R_ W_;…
G106: Start NURBS interpolation P: Degree of a NURBS curve X, Y, Z: Control pointI, J, K: Tool axis vector R: KnotW: Weight (default value = 1)
Experiment
Mechatrolink IIprotocol
<Servo System>Yaskawa S-II
<Control PC>Simultaneous 5-Axis
Control system
NT110 digital commnunication
board
Digital motion network system
PCI slot type
S-II
0 20 40 60 800
5
10
15
20
25
Feed
rate
[mm
/s]
5-Axis NURBS Interpolation Linear Interpolation
Length of Curve [mm]
0 20 40 60 800
1
2
3
4
5
Length of Curve [mm]
Cont
our e
rror [
mm
x 10
-3] 5-Axis NURBS interpolation
Linear interppolation
0 20 40 60 800.000
0.004
0.008
0.012
0.016
To
ol Or
ienta
tion
Erro
r [de
g.]
5-Axis NURBS Interpolation Linear Interpolation
Length of Curve [mm]
Max. allowable chord error for linear interpolation : 1μm Feedrate : 0.9m/m
Feedrate
Contour error
Tool orientation error