Delta Tau GEO BRICK LV User Manual

 

 

If there is neither a vector specification nor a radius specification on a given move command line, the 
move will be linearly interpolated between start and end points, even if the program is in circular move 
mode.  However, cutter compensation will not work properly if this is done.  LINEAR move mode must 
be explicitly declared if cutter compensation is on. 

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.  See the Feedrate Axes section in this manual. 

If the endpoint is not the same distance from the center as the starting point, the change in radius is taken 
up smoothly over the course of the move.  Technically, Turbo PMAC generates an exponential spiral 
curve with a constant vector feedrate and a constant change in radius with respect to time (constant 
dR/dθ). 

When using an IJK center vector, this spiral curve can be created over any angle between the start point, 
the “center” and the end point.  When using the R radius-magnitude specification, a spiral can be created 
only if the distance between the start point and the end point is more than twice the radius magnitude.  In 
this case, the start point, the center, and the end point will all be collinear (like a semi-circle).  For moves 
specified this way, this technique is really used just to permit the execution of semi-circles with some 
tolerance for round-off errors.   

Each coordinate system has an I-variable (Isx96) that determines the limit in distance difference for which 
this compensation will be done.  Above this limit, a run-time error will be generated and the program will 
stop.  This limit allows distinguishing between round-off errors and major mistakes. Regardless of this 
limit, if the distance from starting point to center or from ending point to center is zero, an error will be 
generated and the program will stop.  If the specified vector does not lie in the plane of interpolation, the 
projection of that vector into the plane is used. 

Turbo PMAC computes circular trajectories through a rapid and continuous cubic spline technique called 
“segmentation mode.”  The spline segments are of a time specified by coordinate system variable Isx13 
(in units of milliseconds).  Typically a value of 5 to 10 milliseconds will be used, depending on the 
number of axes being controlled by the card.  When Isx13 is greater than zero, all blended moves – linear 
and circular – are computed through this ongoing cubic spline technique.  The exact move calculations 
are performed every Isx13 milliseconds, and fine interpolation between these intermediate points is done 
at the servo update rate using an efficient cubic B-spline interpolation (identical to Turbo PMAC’s 
SPLINE1 mode).  

If Isx13 is zero, linear moves are not computed using this spline technique and circular moves are not 
permitted (if a circular move is requested, it will be done as a linear move).  The difference in the actual 
performance of linear-mode moves between Isx13=0 mode and Isx13>0 mode is virtually imperceptible, 
unless the feature sizes of the moves are in the same range as the Isx13 time. 

Segmentation mode (Isx13 > 0) also is required to use cutter-radius compensation (even if circle moves 
are not explicitly programmed), kinematic calculations, and the special lookahead buffer.