Torque Monitoring or Payload Calculation

    Hello all,

    I have a KUKA robot picking and placing objects. The objects are on a machine in two parts, 1 part stays in the machine and the other is picked up, emptied, and put back by the robot. The halves are aligned with alignment pins.

    Very occasionally the robot will pick the half up with the other half (i believe the alignment pins are snagging).

    This doesn't happen very often but it would be nice if I could use torque monitoring or a payload calculation to combat this. E.g. once the robot has picked up the half, do a check to make sure the torque/payload is correct and then continue, if too heavy then stop and flag an alarm on the HMI.

    Is this possible? Apologies if this is a basic question but I don't have much experience with robots.

  • Fubini November 13, 2023 at 3:09 PM

    Approved the thread.

    What's the weight of the parts? What's the weight fo the gripper? How big is your robot?

    Don't think that it's possible to detect the difference between one or two parts gripped, the difference in motor current will be too small, if the part weight isn't that big in respect to robot size.

    Attach some sensors to the gripper or somewhere else to detect the problem, will be much more reliable.

    KUKA robots allow monitoring of the motor current or torque (torque is proportional to current). this means it is possible to write program to react on certain value. this will be something to dial in through trial and error or by recording all known loads and do a comparison. the thing to keep in mind is that you probably want to do this while robot is not moving (pause motion to do a check) which adds cycle time. this is why using sensor is preferred (and it is usually simpler).

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

    Hi guys. thank you for your responses.

    I believe the robot has a 240kg capacity. The weight of the parts are roughly 100kg each, so i would be trying to work out if i have picked up 100kg or 200kg. Is this doable?

    Unfortunately i am unable to use sensors for this due to the nature of the machine.

    Try it. It is not too complicated to watch the current, you can just have a look into it during the normal production, and you can see the difference.

    2 times 100 kg on an 240kg Robot? So your gripper maximum weight is 40 kg, and only if the mass Centerpoint is not more than 200 mm away from flange.

    Think Your robot is overloaded. :winking_face:

    there is no gripper. the tool on the robot is rated for 400kg i believe so should be all good there. its a basic tool with a lock/unlock function and the parts have a female part for the tool to connect to.

    under normal circumstances it should only be lifting 100kg, its only when something goes wrong it may be lifting the 200kg. i just want the robot to stop if it does rather than carry on and risk damaging anything.

    Quote from rishabcps

    Could you please suggest some sensors to detect the payload?

    What do you want to detect? Given this thread, I'm going to assume you want to detect the payload Mass, CoG, and Inertia.

    If you want to detect the payload one time, during setup, then Panic's recommendation is probably the right way to go. It should be noted that measuring the Mass value separately (usually by putting the payload on a scale) and entering that manually will increase the accuracy of KUKA Load Determination.

    If you want to dynamically detect the payload to write into $LOAD, then you may have to look at Force-Torque sensors like those made by ATI.

    The problem is similar to the initial question. I have a pick and place application for which I need to confirm if the part has been picked up by the robot. Torque monitoring on the robot is not reliable. FT sensor seems expensive and an overkill. I was thinking of optical sensors attached to the gripper to confirm the part but wondering if there are any other ways to confirm the presence of the part on the gripper?

    Thanks.

    Closed-loop sensing is always the best way. Often it can be as simple as sensing the position of the gripper fingers -- to be effective, grippers need to close at least a bit further than the minimum size of the part, so I've often used "overtravel" sensors that indicated that the gripper had closed all the way to the hard stops, and thus could not have a valid part gripped.

    Many "smart" grippers use torque feedback, like those from Robotiq.

    And putting prox sensors or photoeyes on a gripper to detect a part is pretty standard. Of course, the trick is always finding ways to ensure the sensors aren't falsely triggered by tooling, or degraded by dust, or other non-obvious issues, which always turns into an interesting exercise. Often you want to have multiple sensors that detect the part in different ways, and check how well they agree.

Advertising from our partners