Rockwell Automation 1771-QB Linear Pos. - Manual (Page 113)

Formatting Module Data (WRITES)
Chapter 7
7Ć34
Bit 0 – Start
Bit 0 in the first axis control word is the start bit. The transition of this bit from
low to high (0 to 1) signals a software start command. Upon receiving this
command, the module begins the setpoint or motion segment move specified in
axis control word 2. In manual mode, this transition causes the module to report
a programming error in the status block and abort the move.
As long as the start bit remains high, (i.e. 1), you can also initiate software start
commands and thus movement to a new position by:
sending a new setpoint or motion segment number
sending a new position, velocity, acceleration, or deceleration parameter for
setpoint 13 when setpoint 13 is the selected setpoint
If you issue software start commands while the axis is in motion (often referred
to as “changing setpoints on the fly”), the new setpoint or motion segment will
supersede the old one. When the new endpoint can be achieved with the current
axis motion, the axis will accelerate or decelerate to the final velocity for this
new move. If the new endpoint is in the opposite direction of the current axis
motion, the axis will stop before reversing and proceeding on to the new
endpoint. The module applies the following criteria in using the old and new
parameters when a software start command is issued with the axis in motion:
the new position, velocity and acceleration parameters will always replace
the old ones for the rest of the move.
if velocity smoothing is disabled, the deceleration parameter can be increased
but not decreased. Thus, if the new deceleration parameter is lower than the
old one, it is ignored until axis motion stops.
if velocity smoothing is enabled, the new deceleration parameter is ignored
until axis motion stops.
if the axis has to stop and change direction to achieve the new endpoint, the
new deceleration parameter will always be used for the portion of the move
in the opposite direction.
for incremental setpoint moves, the module calculates the new endpoint
relative to the endpoint for the old move.
for incremental motion segment moves, the module calculates the new
endpoint relative to the current axis position.
if a programming error is detected in the new setpoint or motion segment
data, the new move is aborted and motion continues to the endpoint specified
in the old data.