Rockwell Automation 1771-QA Stepper Positioning Assembly User Manual - Manual (Page 71)

3–49 Programming and Operation
Publication 1771-UM002A–EN–P – May 2000
Decel and Position Considerations for a 0Hz Rate Move
A 0Hz rate move must be used when the profile is brought to a stop
such as when reversing direction. When programming a 0Hz rate
move, the ramp time and decel time are not used by the stepper
controller module regardless of whether or not they are programmed.
Only the rate (0Hz) and final position values are entered. Either one
of the following equations can be used to verify that a move to 0Hz
rate allows 20ms of final rate before the decel begins. This
constraint should be considered when any move in the continuous
mode except the last move is brought to a 0Hz rate.
If the actual executed decel time T is more important than the final
position, then equation 2a should be used to calculate the correct
DELPOS from which the correct programmed final position value
can be obtained.
DELPOS |Programmed final position - starting position|. The ||
symbols means absolute value; disregard the sign in the answer.
If a required final position of the move to 0Hz rate is more important
than the actual executed decel time, equation 2b should be used to
verify that the decel time T does not exceed 9.99 seconds.
Equation 2a: Final Position Value
+ 0.04
2
T
DELPOS = IR and
Final Position Value = DELPOS + Final Position of the Previous
Move.
Equation 2b: Actual Decel Time
T
DELPOS
IR
– 0.04
where:
DELPOS = The difference in number of pulses between the
starting position of the move and the programmed final
position of the move.
T = The actual time of the decel in seconds as executed by
the positioning system (programmed ramp and decel times of
the move are ignored).
IR = Initial rate in pulses per second (final rate of the
previous move).