Delta Tau GEO BRICK LV Manual Do Utilizador

 

The first 360 pieces will be blended (splined) together on the fly as Turbo PMAC cycles through the inner 
loop.  But when PMAC increments P2 to 360, it hits the first ENDWHILE and jumps back to the inner 
WHILE condition, which is now false, so it jumps down, increments P1, hits the second ENDWHILE, and 
jumps back to the outer WHILE condition, all without encountering a move command. 
At this point, Turbo PMAC invokes the double-jump-back rule and lets the last programmed move come 
to a stop.  It does this to prevent the possibility that it might be caught in an indefinitely true set of loops 
with no movement, which could mean that it would not have the next move equations ready in time.  It 
resumes calculations when this move has finished and will start up the next sequence of moves in the 
inner loop.   

To blend all of these moves together continuously, pull the last move of the inner loop outside of the 
inner loop.  This way, never will two ENDWHILE statements be encountered between move commands: 

SPLINE1 TM20 

P1=0 

WHILE (P1<10) 

 P2=0 
 WHILE 

(P2<359) 

 ; Note that loop stops earlier 

  X(P1*SIN(P2)) 

  P2=P2+1 

 ENDWHILE 
 X(P1*SIN(P2)) 

 ; Last move from inner loop 

 P1=P1+1 

ENDWHILE 

Looping to Wait: 

There are several methods for holding program execution while waiting for a certain condition to occur.  
Usually, this is done with a WHILE loop, but what is done inside the loop has an effect on responsiveness 
and calculation load.   

The fastest execution is the WHILE({condition}) WAIT loop.  As soon as the WAIT command is 
encountered, motion program calculations are suspended until the next real-time interrupt, at which time 
they will re-evaluate the condition.  The motion program effectively becomes like a one-line PLC 
program.  If the next RTI has already occurred, it will immediately re-enter the interrupt service routine 
and re-evaluate the condition.  If this occurs repeatedly, background routines will be starved for time, 
slowing PLCs and communications, or in the worst case, tripping the watchdog timer.  Usually this 
happens only if multiple coordinate systems are in simultaneous WHILE...WAIT loops. 
Of similar speed is an empty WHILE...ENDWHILE loop, or at least one with no motion commands 
inside.  Each RTI, this will execute twice, stopped by the double-jump-back rule.  Calculations resume at 
the next RTI, or if this has occurred already, they resume immediately, with the same possible 
consequences for starving background calculations. 

Using a WHILE({condition}) DWELL single-line loop helps to control the looping rate better, 
giving time for background routines.  The condition is evaluated only once after each DWELL. 

Implications of Calculating Ahead 

The need of the motion program to calculate ahead during a continuous sequence of moves means that 
non-motion actions –particularly the setting of outputs – taken by the program happen before you might 
think they would – by one or two moves.  For variables that are only used within the program, this is no 
problem, because everything happens sequentially within the program. 

It is possible to move these non-motion actions to a point one or two moves later in the program to get the 
actions to occur when they are desired.  However this makes the program extremely difficult to read as far 
as the proper sequence of operations.