NI SoftMotion Axis Jumps Position Intermittently and Causes Drive Fault

Updated Jan 31, 2018

Reported In

Software

  • LabVIEW 2015 SoftMotion Module
  • LabVIEW 2016 SoftMotion Module

Issue Details

The position of the motor jumps intermittently during certain move sequences with a SoftMotion axis. This leads to drive faults, errors or unstable motion movements on my system. How can I troubleshoot this and what are the potential causes?

Solution

There are two possible causes for this behavior and they are explained below.

1. Improper Gain Values
The most likely cause of a sudden change in position, is an improper set of move parameters, mainly the velocity, acceleration and non-optimal drive tuning. Using improper/unstable gain values for the motor tuning, can cause a very large change in velocity when running in position mode. This can cause drive safeguards, such as position errors and current limits to kick in. As such, these parameters will need to be programmed appropriately for your application.

2. Corruption From Multi-Core Processors
Apart from the issue explain above, if you observe that the move or sequence of moves executes normally and only intermittently shows the position jump, it might be caused by a known issue with SoftMotion running on multi-core processors. 

On multi-core real-time processors using any version of the LabVIEW SoftMotion Module prior to October 2016, it is possible for the position data to be corrupted before a move is executed. This results in a large position error causing the axis to attempt to move to the new set point in one Scan Engine period, possibly causing an over-speed fault or other errors.

This issue has been resolved in a software patch for LabVIEW SoftMotion Module versions 2015, 2015 SP1 and 2016. Ensure that you are running the latest version of these modules.

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