Rockwell Automation 1771-QA Stepper Positioning Assembly User Manual - Manual (Page 66)

3–44 Programming and Operation
Publication 1771-UM002A–EN–P – May 2000
The values which can be selected for ramp and decel times, the final
rate, and final position allow a very wide variety of move profiles to
be programmed. However there are some constraints which, if not
taken into consideration, can result in a programming error when the
move profile is executed. These constraints, for the most part,
should be considered when programming long acceleration times
with brief but relatively high final rates.
Selected values can be tested on paper using one or more of the
following algebraic equations as appropriate. This can be done by
substituting the selected values into the equation, performing the
required mathematical manipulations and seeing whether the
constraints are satisfied. Values can also be tested by running the
program with the stepper translator disconnected. If the constraint(s)
are not met as indicated by a programming error, then new values
can be selected and tested until allowable values are found.
Move Duration
A move must remain at the programmed final rate for at least 20ms
in order to avoid a programming error. This constraint must be
satisfied for all moves but could likely be exceeded in moves
covering short distances at high final rates. This constraint can be
met in either of two ways:
•
Decide where the final position must be. Then select and/or
adjust the programmed ramp time, decel time (if part of the
move) and/or final rate values accordingly.
•
Select appropriate programmed ramp time, decel time (if part of
the move) and/or final rate values and accept the resulting final
position.
The following equation can be used to test this constraint.
Equation 1.
RT (FR + IR)
+ FR
DT
+ 0.02 < DELPOS
2 2
where:
RT = ramp time
FR = final rate
IR = initial rate
DT = decel time (in the continuous mode, this term is zero
for all but the last move)
DELPOS = Difference in ELapsed POSition, the difference
in number of pulses between the starting position and
programmed final position of the move
Application
Considerations