Time Related Parameters of the Controller and Communication

Period of the State Messages

We have tested how low we can go with the period of the joint position messages from the controller. We have tested delay values from 100 to 0 ticks. When we tried to go under the 5 ticks delay the controller stops sending messages completely. Other measurement shows that the message generation and processing in the controller can take up to 15 ms depending on the work load of the overall system and the priority assigned to the task. This lead us to select 10 ms period with the NORMAL priority as a good tradeoff. The period is currently parameter and can be set through pendant.

MotoPlus Stop Watch Accuracy

The MotoPLus library provides mpStopWatchXXX functions for time measurement, but the accuracy is not very good. The manual state that the accuracy decrease with increase of the length of time measured, but should be less than 10 ms. In addition the usage of these functions is bit awkward.

System Clock Accuracy

In addition to MotoPlus API it is possible to use the VxWorks API, which provides system time through clock_gettime function. Accuracy is to be estimated?

Latency Measurement

See latency_report.pdf

Related tasks

  • #122 Synchronize ROS time and DX-100 time
  • #107 DX 100 Time response measurement
  • #53 Measure the state server loop.
  • #55 Measure the feedback loop.



Attached files

latency_report.pdf (283 KB) Libor Wagner, 12/19/2012 11:24