Can I Use Analog Feedback with SoftMotion?

Updated Jan 4, 2018

Reported In


  • LabVIEW SoftMotion Module

Issue Details

My motion control application requires controlling a motor with respect to a form of analog feedback (pressure sensor, load cell, etc.) instead of an encoder. Does SoftMotion support analog feedback?


SoftMotion is primarily a position-based motion controller which requires position feedback, typically an encoder, for closed-loop control. For simple applications, such as varying motor velocity with respect to an analog input at low frequency, commanding a Velocity Override with SoftMotion will suffice. However, there are no native hardware or software options for using analog feedback for high speed control loops with SoftMotion. 

It is possible to use the SoftMotion API to develop custom control loops that would allow for analog feedback on the FPGA. However, it is up to the user to determine, write, and test the algorithms and control loop implementation needed for their application. For small motion applications, the NI 950x Drive Modules provide low-level FPGA control loops as a starting point for customization.

If you are using a supported EtherCAT motor drive, the SoftMotion API allows you to write torque setpoints in Profile Torque Mode. This allow you to bypass the position and velocity loops and directly command the drive's torque loop. Updates to the torque setpoint and are commanded at the Scan Engine rate. See SoftMotion Drive Interface (SDI) Plug-in Feature Compatibility for a compatibility guide detailing supported drives that use the drive-based torque mode. 


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