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matthewd92matthewd92 Posts: 385Founding Pro, Tactile Sensor Beta Testers Handy
We were trying to do some work today with the FT150, both teaching a path as well as just moving it around to various waypoints.  We kept getting an error though about the robot cannot operate in force mode when in a singularity.  As far as we could tell the robot was not in any type of singularity.  Is there a range of motion that the force mode does not operate within?  Here is an example of one of the positions that we were in when we received the error.


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  • Nicolas_LauzierNicolas_Lauzier Posts: 24Beta Tester VIsion 1.1 Program Crew
    Hi @matthewd92,

    Our Active Drive guiding mode works inside of the UR force mode in order to have stable contacts (which is helpful  when using a part to guide the tool). This mode is more restrictive than the normal motion of the robot. The exact metric that they use to trigger this popup is however not documented.

    Ideally, we would restrict the motion of the Active Drive mode to make sure we never see this error. I will request this feature to UR such that we may include it in a future version of the sensor URCap.

    Meanwhile, the only thing I would suggest is to stay as far away as possible of the singularities. I understand that in the above picture you are not in a singularity if your TCP is defined at the tip of the fingers. However, my guess is that the force mode may be using the tool flange of the robot in its computation, in which case the robot pose is close to the axis of the first joint (I think the controller forbids a cylinder zone around the axis of the first joint).

    Nicolas Lauzier, Eng., PhD
    R&D Director
    nicolas@robotiq.com

  • matthewd92matthewd92 Posts: 385Founding Pro, Tactile Sensor Beta Testers Handy
    Thanks. It would be great if UR could document the envelope where force mode doesn't work. @Stefan_Stubgaard is that something that could be done?
  • Good suggestion @matthewd92 I will bring this back into UR.

    In general the robot should be able to operate with force mode almost within the normal singularity limits, slightly more restrictive.

    The typical areas where singularity can happen for a UR robot is:

    • Cylindrical area around base (as pictured in user manual)
    • When elbow is close to 0 degrees (arm close to fully stretched)
    • Wrist 1 and wrist 3 are close to being parallel

    In the first picture in your first post, the error can be caused if robot is moving linear towards you (in depth direction of picture), as the tool flange is close to the cylindrical area and base joint will have a rapid movement to keep the linear trajectory of TCP, possibly causing a singularity error.

  • @Beachy Here is what Robotiq + UR is saying about this issue.

    Catherine Bernier, Jr. Eng. 
    Application Engineer at Robotiq
    c.bernier@robotiq.com
    https://www.linkedin.com/in/catherinebernier
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