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abeachy_HG24abeachy_HG24 Posts: 79 Handy
edited November 2016 in Programming
Hi pros,
I am working with some UR 10s and we are experiencing what seems to be like completely random protective stops. I will run a program 7 or 8 times flawlessly and then I will run it again without changing anything and I will get a protective stop. I've talked to UR and they suggested reducing the acceleration but 20% each time it happens. They are thinking we might be running it right on the borderline for protective stops so that is why it's only every once in a while. That concerns me a little because there's no way to know if we are right on the border besides running the program many times, and we are on a crunch for time. Has anyone else seen this happen? Also, any tips on how we can avoid this? We could slow it down, but we are pushing it because of cycle time.

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  • matthewd92matthewd92 Posts: 927Founding Pro, Tactile Sensor Beta Testers Handy
    @abeachy_HG24 I'd love to say I've never seen this but I have. It usually plagues us on projects where we are pushing them to the limit. I agree with UR about the acceleration. One of the things I wish we could do is define separate accel and decel values but we can't. Have you tried blending the moves?  You may also want to put two waypoints with a blend so that one can be the accel and one the decel allowing you to slow down over a longer period. 

    Another thing to check is that your TCP weights and center of gravity are set correctly. Have you weighed the total payload accurately?  This becomes more critical as you start using the full length of the arm. 

    Where re are you seeing the protective stops?  Does it generally happen at a point that is an end point, meaning the robot is stopping there?
  • abeachy_HG24abeachy_HG24 Posts: 79 Handy
    @matthewd92 Generally whenever I see these protective stops, it is during a blend. I have adjusted the blends down as low as 20 mm on a couple of occasions where this was happening and I would get the same thing. What do you mean by two waypoints with a blend?

    I believe so. Usually the protective stop occurs whenever the robot is not carrying anything. For the  Robotiq 85 and our custom gripper pads, I have the payload set at .9 kg. How precise does it need to be? A lot of the stuff the robot is picking up is very light, probably less than a pound.

    It depends, I have seen it happen at an end point. I have also seen it on a waypoint that has a blend radius on it and fixed waypoints before and after that waypoint.
  • Etienne_SamsonEtienne_Samson Posts: 416Beta Tester Beetle, Wrist Camera URCap 1.3.0, Vacuum Beta tester Handy
    @abeachy_HG24 if you push the robot speed it's usually quite important to have the proper TCP with the correct CoG like @matthewd92 said . Once you get that, you will need a dynamic payload adjustment.

    In your program, you should set the payload to whatever you have, also set it when you have nothing picked. That will help you a lot if you want to speed up and avoid those. I'd say if you pick anything over 100 g you should adjust your payload.

    We just updated the tables for mass and CoG. We will add something for the TCP shortly, otherwise you can approximate from the Gripper tech drawings.
    Etienne Samson
    Technical Support Director
    +1 418-380-2788 ext. 207
    [email protected]
  • matthewd92matthewd92 Posts: 927Founding Pro, Tactile Sensor Beta Testers Handy
    @abeachy_HG24 what I was referring to is if I want to go from a fixed point where I am currently at, say a pick point, to a second fixed point, say where I am placing the part and I want to get there very fast so max accel and velocity.  You might need to decelerate slower than you accelerate depending on the conditions of the robot.  For instance, if you are picking close to the robot but placing near the end of the reach you may need to decelerate slower than you accelerated just due to the arm dynamics.  TO accomplish this you could put a second point in the move and blend it with the end point such that the middle point would be your acceleration point, and now your end point could be the deceleration point.  The points could have the same velocity but this allows you to achieve a difference in the acceleration and deceleration values.  Other motion systems I have worked with (including robots) allow you to specify accel and decel separately for any move allowing you to more finely control the motion.  UR in their quest to make a robot that is easy enough for anyone to use has not included this functionality so this is a potential work around.
  • Etienne_SamsonEtienne_Samson Posts: 416Beta Tester Beetle, Wrist Camera URCap 1.3.0, Vacuum Beta tester Handy
    @matthewd92 that's very interesting I never did that, I'll try to remember it!
    Etienne Samson
    Technical Support Director
    +1 418-380-2788 ext. 207
    [email protected]
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