Delta Tau GEO BRICK LV Manual De Usuario
Turbo PMAC User Manual
314
Writing and Executing Motion Programs
Lookahead Length Parameter
Variable Isx20 for the coordinate system tells the algorithm how many segments ahead in the program to
look. This value is a function of the number of segments that must always be correct in the lookahead
buffer (SegmentsNeeded). The formula is:
look. This value is a function of the number of segments that must always be correct in the lookahead
buffer (SegmentsNeeded). The formula is:
eded
SegmentsNe
*
3
4
20
Isx
=
Setting Isx20 to a value larger than needed does not increase the computational load (although it does
increase the time of heaviest computational load while the buffer is filling). However, it does require
more memory storage, and it does increase the delay in having the program react to any external
conditions.
Setting Isx20 to a value smaller than needed does not cause the limits to be violated. However, it may
cause Turbo PMAC to limit speeds more severely than the Ixx16 limits require in order to ensure that
acceleration limits are not violated. Also, a saw-tooth velocity profile may be observed.
increase the time of heaviest computational load while the buffer is filling). However, it does require
more memory storage, and it does increase the delay in having the program react to any external
conditions.
Setting Isx20 to a value smaller than needed does not cause the limits to be violated. However, it may
cause Turbo PMAC to limit speeds more severely than the Ixx16 limits require in order to ensure that
acceleration limits are not violated. Also, a saw-tooth velocity profile may be observed.
Defining the Lookahead Buffer
In order to use the lookahead function in a Turbo PMAC coordinate system, a lookahead buffer must be
defined for that coordinate system, reserving memory for the buffer. This is done with the on-line
coordinate-system-specific DEFINE LOOKAHEAD command. Because lookahead buffers are not
retained through a power down or reset, this command must be issued after every power-up or board
reset.
There are two values associated with the DEFINE LOOKAHEAD command. The first determines the
number of motion segments for each motor in the coordinate system that can be stored in the lookahead
buffer. At a minimum, this must be set equal to Isx20.
If this value is set greater than Isx20, the lookahead buffer stores historical data. This data can be used to
reverse through the already executed trajectory. If reversal is desired, the buffer should be sized to store
enough back segments to cover the desired backup distance. There is no penalty for reserving more
memory for these synchronous M-variable assignments than is needed, other than the loss of this memory
for other uses.
The room reserved for the segment data in the lookahead buffer is dependent on the number of motors
assigned to the coordinate system at the time of the DEFINE LOOKAHEAD command. If the number of
motors assigned to the coordinate system changes, the organization of the lookahead buffer will be
wrong, and the program will abort with a run-time error on the next move after the coordinate system is
changed.
If the coordinate system must be changed during an application that uses lookahead, the lookahead buffer
must first be deleted, then defined again after the change. The following motion program code shows
how this could be done:
defined for that coordinate system, reserving memory for the buffer. This is done with the on-line
coordinate-system-specific DEFINE LOOKAHEAD command. Because lookahead buffers are not
retained through a power down or reset, this command must be issued after every power-up or board
reset.
There are two values associated with the DEFINE LOOKAHEAD command. The first determines the
number of motion segments for each motor in the coordinate system that can be stored in the lookahead
buffer. At a minimum, this must be set equal to Isx20.
If this value is set greater than Isx20, the lookahead buffer stores historical data. This data can be used to
reverse through the already executed trajectory. If reversal is desired, the buffer should be sized to store
enough back segments to cover the desired backup distance. There is no penalty for reserving more
memory for these synchronous M-variable assignments than is needed, other than the loss of this memory
for other uses.
The room reserved for the segment data in the lookahead buffer is dependent on the number of motors
assigned to the coordinate system at the time of the DEFINE LOOKAHEAD command. If the number of
motors assigned to the coordinate system changes, the organization of the lookahead buffer will be
wrong, and the program will abort with a run-time error on the next move after the coordinate system is
changed.
If the coordinate system must be changed during an application that uses lookahead, the lookahead buffer
must first be deleted, then defined again after the change. The following motion program code shows
how this could be done:
DWELL 10
; Stop lookahead execution
CMD "&1 DELETE LOOKAHEAD"
; Delete buffer
CMD "&1 #4->100C"
; Assign new motor to C. S. 1
CMD "&1 DEFINE LOOKAHEAD 1000,100" ; Redefine buffer
DWELL 10
DWELL 10
; Make sure commands execute
The second value associated with the DEFINE LOOKAHEAD command determines the number of
synchronous M-variable assignments (e.g. M1==1) for the coordinate system that can be stored in the
lookahead buffer. Synchronous M-variable assignments in the motion program delay the actual
assignment of the value to the M-variable until the start of actual execution of the next move in the
motion program. Therefore, these actions must be held in a buffer pending execution.
synchronous M-variable assignments (e.g. M1==1) for the coordinate system that can be stored in the
lookahead buffer. Synchronous M-variable assignments in the motion program delay the actual
assignment of the value to the M-variable until the start of actual execution of the next move in the
motion program. Therefore, these actions must be held in a buffer pending execution.