Delta Tau GEO BRICK LV User Manual
Turbo PMAC User Manual
Writing and Executing Motion Programs
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Feedrate Override
All lookahead calculations are performed assuming a feedrate override value of 100%. If the feedrate
override value, from whatever source, changes from 100%, the velocity and acceleration calculations will
be incorrect. True velocity values vary linearly with the override value; true acceleration values vary with
the square of the override value.
override value, from whatever source, changes from 100%, the velocity and acceleration calculations will
be incorrect. True velocity values vary linearly with the override value; true acceleration values vary with
the square of the override value.
For example, at 200% override, velocity values are twice the programmed values (and could exceed the
limit values by a factor of 2), and acceleration values are four times the programmed values (and could
exceed the limit values by a factor of 4).
limit values by a factor of 2), and acceleration values are four times the programmed values (and could
exceed the limit values by a factor of 4).
Because the feedrate override can be changed at any time with immediate effects, the lookahead function
cannot anticipate what the override will be when the move will actually be executed. Therefore, it cannot
plan for any changes in the override, so it assumes operation at 100%.
cannot anticipate what the override will be when the move will actually be executed. Therefore, it cannot
plan for any changes in the override, so it assumes operation at 100%.
The basic idea of lookahead is to remove the override function from the instantaneous judgment of the
operator, and instead use the mathematical calculations of the controller, which effectively act as an
override, to ensure proper and optimal execution of the path.
operator, and instead use the mathematical calculations of the controller, which effectively act as an
override, to ensure proper and optimal execution of the path.
Computational Capabilities
The lookahead calculations can put significant real-time calculation loads on the Turbo PMAC processor.
If the processor fails to keep up with these real-time requirements, program execution will fail with a
“run-time” error, and motion will be aborted. There is also a slight possibility of a watchdog timer trip if
the processor is never released from the foreground lookahead calculations for background tasks.
If the processor fails to keep up with these real-time requirements, program execution will fail with a
“run-time” error, and motion will be aborted. There is also a slight possibility of a watchdog timer trip if
the processor is never released from the foreground lookahead calculations for background tasks.
It is important that the application be evaluated to ensure that the lookahead calculations can be
performed properly under the worst-case conditions. The period when the most intensive calculations are
being performed is at the beginning of a move sequence, when Turbo PMAC is filling the buffer
dynamically to get ahead the specified distance.
performed properly under the worst-case conditions. The period when the most intensive calculations are
being performed is at the beginning of a move sequence, when Turbo PMAC is filling the buffer
dynamically to get ahead the specified distance.
A good worst-case test is to run a motion program with programmed moves at the maximum move-block
rate right at the beginning of a blended sequence. Make sure that the Turbo PMAC can get through this
combination of high block-rate execution and dynamic filling of the lookahead buffer. To establish a
margin of safety, increase the override value above 100% to see what extra capability exists. A 20%
margin (proper execution at 120%) is strongly recommended.
rate right at the beginning of a blended sequence. Make sure that the Turbo PMAC can get through this
combination of high block-rate execution and dynamic filling of the lookahead buffer. To establish a
margin of safety, increase the override value above 100% to see what extra capability exists. A 20%
margin (proper execution at 120%) is strongly recommended.
Stopping While In Lookahead
If you wish to stop axis motion while in lookahead mode, he must carefully consider how the stopping is
to be done. It is important to realize what point in the chain of execution is being halted with the stopping
command. Different stopping commands have different effects, and different uses.
to be done. It is important to realize what point in the chain of execution is being halted with the stopping
command. Different stopping commands have different effects, and different uses.
Quick Stop
The \ quick-stop command causes Turbo PMAC to immediately calculate and execute the quickest stop
within the lookahead buffer that does not exceed Ixx17 acceleration limits for motors in the coordinate
system. Motion continues along the programmed path to a controlled stop, which is not necessarily at a
programmed point (and probably will not be). This command is the effective equivalent of a feedhold
within lookahead (even though the internal mechanism is quite different), and it should be the command
issued when an operator presses a Hold button during lookahead. Outside of lookahead, this command
causes an actual feed hold, as if the H command had been given.
within the lookahead buffer that does not exceed Ixx17 acceleration limits for motors in the coordinate
system. Motion continues along the programmed path to a controlled stop, which is not necessarily at a
programmed point (and probably will not be). This command is the effective equivalent of a feedhold
within lookahead (even though the internal mechanism is quite different), and it should be the command
issued when an operator presses a Hold button during lookahead. Outside of lookahead, this command
causes an actual feed hold, as if the H command had been given.