User`s manual

5.0 - Motion Programs
Page - 50
Starting point
i (inc)
j
(inc)
X (inc)
Y (inc)
End
p
oint
Center
Starting point
j
(abs)
i (abs)
Y (abs)
X (abs)
Center
0,0
End
p
oint
Y
X
Z
k-1
X X
Y Y
5.7 - Circular Interpolation
PMAC allows circular interpolation on the X, Y, and Z axes in a coordinate system. As with linear blended moves, TA and
TS control the acceleration to and from a stop, and between moves. Circular blended moves can be either feedrate-specified
(F) or time-specified (TM), just as with linear moves. It is possible to change back and forth between linear and circular
moves without stopping. This is accomplish by entering the command LINEAR when linear interpolation is needed and
CIRCLE1 or CIRCLE2 for circular interpolation.
1) PMAC performs arc moves by segmenting the arc and performing the best cubic fit on each segment. I-variable I13
determines the time for each segment. I13 must be set greater than zero to put PMAC into this segmentation mode in
order for arc moves to be done. If I13 is set to zero, circular arc moves will be done in linear fashion.
The practical range of I13 for the circular interpolation mode is 5-10 msec. A value of 10 msec is recommended for
most applications, a lower than 10 msec I13 value will improve the accuracy of the interpolation (calculating points of
the curve more often) but will also consume more of the PMAC’s total computational power.
2) When PMAC is automatically segmenting moves (I13 > 0), which is required for Circular Interpolation, the Ix17
accelerations limits and the Ix16 velocity limits are not observed.
3) Any axes used in the circular interpolation are automatically feedrate axes for circular moves, even if they were not so
specified in an FRAX command. Other axes may or may not be feedrate axes. Any non-feedrate axes commanded to
move in the same move command will be linearly interpolated so as to finish in the same time. This permits easy
helical interpolation.
4) The plane for the circular arc must have been defined by the NORMAL command (the default -- NORMAL K-1 --
defines the XY plane). This command can only define planes in XYZ-space, which means that only the X, Y, and Z
axes can be used for circular interpolation. Other axes specified in the same move command will be interpolated
linearly to finish in the same time. The most commonly used planes are:
NORMAL K-1 ; XY plane -- equivalent to G17
NORMAL J-1 ; ZX plane -- equivalent to G18
NORMAL I-1 ; YZ plane -- equivalent to G19
5) To put the program in circular mode, use the program command CIRCLE1 for clockwise arcs (G02 equivalent) or
CIRCLE2 for counterclockwise arcs (G03 equivalent). LINEAR will restore you to linear blended moves. Once in
circular mode, a circular move is specified with a move command specifying the move endpoint and either the vector
to the arc center or the distance (radius) to the center. The endpoint may be specified either as a position or as a
distance from the starting point, depending on whether the axes are in absolute (ABS) or incremental (INC) mode
(individually specifiable).
X{Data} Y{Data} R{Data} ;Radius of the circle is given
X{Data} Y{Data} I{Data} J{Data} ;Center coordinates of the circle are given
6) If the vector method of locating the arc center is used, the vector is specified by its I, J, and K components ('I' specifies
the component parallel to the X axis, 'J' to the Y axis, and 'K' to the 'Z' axis). This vector can be specified as a distance
from the starting point (i.e. incrementally), or from the XYZ origin (i.e. absolutely). The choice is made by specifying
'R' in an ABS or INC statement (e.g. ABS (R) or INC (R)). This affects I, J, and K specifiers together. (ABS and
INC without arguments affect all axes, but leave the vectors unchanged). The default is for incremental vector
specification.