Rockwell Automation 1771-QA Stepper Positioning Assembly User Manual - Manual (Page 73)

3–51 Programming and Operation
Publication 1771-UM002A–EN–P – May 2000
This exceeds 9.99 seconds. Either the position of the 0Hz rate move
must be decreased, or the final rate of the previous move must be
raised, or the final position of the previous move must be extended
(or a combination of all three) in order to bring the decel time to
9.99 seconds or less. Assume that the DELPOS can be changed. If
the DELPOS is reduced from 110k to 80k pulses, the actual decel
time will be 10 - 0.04 = 9.96 seconds (from line 2) and within limits.
In order to reduce the DELPOS to 80k pulses, the final position of
the previous move would have to be extended by 30k pulses to 540k
pulses.
Override Ramp Time Considerations
During execution of an override move, the actual override ramp time
executed by the stepper positioning assembly will vary depending on
the rate which is being overridden.
The override move must be programmed to guarantee that both the
actual executed override ramp time and the programmed ramp time
be in the range of 0-9.99 seconds. The actual override ramp time is
defined as the time required to change from the rate-in-process when
the override command was received by the stepper controller module
to the programmed override rate. The actual override ramp time as
executed by the positioning system can be calculated using equation
3a. Equation 3b can be used to verify that a desired actual ramp time
(ORT
Act
) is possible by ensuring that the programmed ramp time
(ORT
Prog
) lies between 0 and 9.99 seconds. These equations should
be used with the maximum and minimum rates which could be
overridden to ensure that the actual override ramp time is between 0
and 9.99 seconds.
The following equations can be used with any (IR) rate to be
overridden.
Equation 3a: Actual Override Ramp Time
ORT
Act
+ ORT
Prog
x
|OFR–IR|
OFR
Equation 3b: Programmed Override Ramp Time
ORT
Prog
+ ORT
Act
x
|OFR–IR|
OFT
where:
ORT
Act
Act = Actual override ramp time
ORT
Prog
= Programmed override ramp time
OFR = Override final rate
IR = Initial rate (rate in process when override occurs)
|OFR - IR| = absolute value (if the difference is a negative
number, consider it positive.)