Reference Manual

PMAC 2 Software Reference
PMAC Program Command Specification 295
Remarks
For a blended circular mode move, both the move endpoint and the vector to the arc
center are specified. The endpoint is specified just as in a LINEAR mode move, either
by position (referenced to the coordinate system origin), or distance (referenced to the
starting position).
The center of the arc for a circular move must also be specified in the move command.
This is usually done by defining the vector to the center. This vector can either be
referenced to the starting point of the move (incremental radial vector mode – the default,
or if an INC (R) command has been given), or it can be referenced to the coordinate
system origin (absolute radial vector mode – if an ABS (R) command has been given).
Alternatively, just the magnitude of the vector to the center can be specified with
R{data} on the command line. If this is the case, PMAC will calculate the location of
the center itself. If the value specified by {data} is positive, PMAC will compute the
short arc path to the destination (<= 180
o
); if it is negative, PMAC will compute the long
arc path (>= 180
o
). It is not possible to specify a full circle in one command with the R
vector specifier.
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 direction of the arc to the destination point – clockwise or counterclockwise – is
controlled by whether the card is in CIRCLE1 (clockwise) or CIRCLE2
(counterclockwise) mode. The sense of clockwise in the plane is determined by the
direction of the NORMAL vector to the plane.
If the destination point is a different distance from the center point than is the starting
point, the radius is changed smoothly through the course of the move, creating a spiral.
This is useful in compensating for any roundoff errors in the specifications. However, if
the distance from either the starting point or the destination point to the center point is
zero, an error condition will be generated and the program will stop.
If the vector from the starting point to the center point does not lie in the circular
interpolation plane, the projection of that vector into the plane is used. If the destination
point does not lie in the same circular interpolation plane as the starting point, a helical
move is done to the destination point.
If the destination point (or its projection into the circular interpolation plane containing
the starting point) is the same as the starting point, a full 360
o
arc is made in the specified
direction (provided that IJK vector specification is used). In this case, only the vector
needs to be specified in the move command, because for any axis whose destination is
not specified, the destination point is automatically taken to be the same as the starting
point.
If no vector, and no radial magnitude is specified in the move command, a linear move
will be done to the destination point, even if the program is in circular mode.
Note:
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.