Delta Tau GEO BRICK LV User Manual

 

 

The next diagram shows how the lookahead function can create a deceleration into a tight corner 
automatically, permitting the corner to be taken slowly to keep it within acceleration constraints, and then 
to accelerate back up to the programmed speed coming out of the corner.  This permits the user to 
command high speeds, and to have Turbo PMAC slow down the path only where needed.  Note that the 
post-lookahead profile in this diagram is not time-extended as it would really be; this was done to show 
the correspondence of points on the profiles. 

Lookahead & Small, Tight Corners

Y

X

Y

X

V

Y

Time

Time

V

Y

V

X

Time

1

2

3

4

5

6

7

1

2

3

4

5

6

7

ACCEL & DECEL

CONTROLLED BY

SPECIFIED G’s

AT CORNER

F50
X10 Y10
X0 Y20

Note how ‘Y” decelerates

to make the corner

Time

1

2

3

4

5

1

2

3

5

4

F50
X10 Y10
X0 Y20

V

X

 

If Turbo PMAC’s inverse kinematic calculations are used, the conversion from tip coordinates to joint 
coordinates takes place before lookahead calculations, segment by segment for LINEAR and CIRCLE 
mode moves.  Therefore, Turbo PMAC can execute the lookahead calculations in joint space, motor by 
motor, even if the system has been programmed in tip coordinates. 

Once the lookahead function has been set up, the lookahead function operates transparently to the 
programmer and the operator.  No changes need to be made to a motion program to use the lookahead 
function, although the programmer may choose to make some changes to take advantage of the increased 
performance capabilities that lookahead provides. 

The following list quickly explains the steps required for setting up and using the lookahead function on 
the Turbo PMAC.  Greater detail and context are given in the subsequent section. 

1.  Assign all desired motors to the coordinate system with axis definition statements. 
2.  Set Ixx13 and Ixx14 positive and negative position limits, plus Ixx41 desired position-limit band, in 

counts for each motor in coordinate system.  Set bit 15 of Ixx24 to 1 to enable desired position limits. 

3.  Set Ixx16 maximum velocity in counts/msec for each motor in coordinate system. 
4.  Set Ixx17 maximum acceleration in counts/msec

2

 for each motor in coordinate system. 

5.  Set Isx13 segmentation time in msec for the coordinate system to minimum programmed move block 

time or 10 msec, whichever is less. 

6.  Compute maximum stopping time for each motor as Ixx16/Ixx17. 
7.  Select motor with longest stopping time. 
8.  Compute number of segments needed to look ahead as this stopping time divided by (2 * Isx13). 
9.  Multiply the segments needed by 4/3 (round up if necessary) and set the Isx20 lookahead length 

parameter to this value.