User manual

78 Rockwell Automation Publication MOTION-UM003F-EN-P - March 2015
Chapter 3 Configure Axis Scheduling
Example Axis Scheduling
Application
Axis Scheduling can improve ControlLogix and CompactLogix EtherNet/IP
Integrated Architecture Motion system performance by reducing average Logix
controller and EtherNet/IP network utilization. Axis Scheduling supports three
separate controller/network motion drive update rates per controller, one rate for
high performance drives, and two additional rates for lower performance drives.
For example, suppose you have a robot removing product from a conveyor belt
that has three precision axes on the robot and four general purpose axes on the
conveyor belt. You would like to configure the controller to run all seven axes at 2
ms to best control the precision axes, but this will take your controller's network
utilization too high. In the past, one option would have been to run all seven axes
8 ms, but this is not fast or precise enough for the robot axes. So you might have
had to add a second controller and Ethernet module to get the performance you
needed. Axis Scheduling lets you configure the axes at different rates based on the
needs of the application, balancing the motion performance and network
utilization of your controller.
With Axis Scheduling, you can configure the axes on the robot to run at a high
base update rate (2 ms) and then configure the conveyor to run at a slower update
rate (8 ms).
Being able to configure three update periods, the four conveyor axes can run as a
single channel, thus appearing to the controller as a single drive. The axes are
updated round-robin style; every 2 ms, three of the robot axes are updated as well
as one of the conveyor axes.
During the next update, three robot axes are updated and then the next conveyor
axis is updated; eventually all conveyor axes are updated and the process starts
again. The controller updates four axes every update period. The controller can
handle the load of four axes easier than a load of seven axes. This improves the
performance of the controller.