Operation
Theory of Operation
QuickStick HT User Manual
235
Rockwell Automation Publication MMI-UM007F-EN-P - September 2020
Figure 6-6: Vehicle Motion Profile Showing Thrust Limitations
In Queue
Typically, vehicles queue up while in route to a particular destination when another vehicle
obstructs the route. Obstructions are normal occurrences, jams are not. While in queue, the
vehicles can be as close together as permitted by the system. The amount of space in between
the carriers that are mounted on the vehicles depends on the defined length of the vehicle. All
vehicles in the queue report being obstructed.
An obstruction indicates that something that the system knows about is keeping the vehicle
from completing its current motion order. This obstruction could be another vehicle, a node
not ready for a vehicle, or a path that is suspended or has not completed startup. Once the
obstruction clears (that is the obstructing vehicle moves, the node becomes ready, or the path
becomes available) the obstructed vehicle is free to complete its order.
A jam indicates that there is no known obstruction keeping the vehicle from moving, but the
vehicle is not moving towards its destination. This lack of progress is typically due to an
unknown obstruction (something having fallen onto the track) or friction within the system
that cannot be overcome. Once the jam has been cleared, typically by outside intervention, the
vehicle is free to complete its order and any vehicles it has obstructed are free to complete
their orders. Other causes of a vehicle being unable to move that are considered a jam are:
•
A vehicle is commanded to move with a velocity of zero.
•
A vehicle is commanded to move with an effective PID set equal to zero.