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Hennie
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Demo_Force_Twist_Release program tripping with C204A3:Sudden Stop Detected Fault |
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/ Most recent by matthewd92 |
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We have sold some torque force sensors recently and the client experimented with the RobotIQ – Demo_Force_twist_release program. He found that the force feedback works great and the program performs well.
He did have a problem with the speed though: Whenever he increased the (Speed_inc) variable for axis 6 only (or wrist 3 in the UR world) to greater than 0.33 the robot would trip with error
C204A3: Sudden stop detected
Now we are guessing that we are breaking one of the speed or acceleration rules, we would just like some clarity on the meaning of the value 0.33 and if there was anything else ( within the demo program) that we could do to increase the speed of that motion.
Thanks Hennie
Basically what happens is that the robot will still physically be in motion after the loop exits, and depending on the next command the joints will have no movement parameters from the controller and will try to immediately stop. This causes either the error you are seeing (sudden stop) or another error that says "invalid set point."
There are two ways around this: Slow the movement down if acceptable, or add a "stopl(a)" command right after the loop. stopl(a) [or stopj(a)] is a command that sends a command to decelerate the robot at value "a." stopl() is for linear stop, and stopj() is for decelerating in joint space, and units will be m/s/s or rad/s/s respectively. The stop command will still only work up to a certain limit though, and requires some trial and error.
Grady I think you are right. @JeanPhilippe_Jobin will be able to elaborate more on the speed_inc variable.
I saw some error with loops once that I think was also related to this. When I hit play, if the loop has no delays in it or position speeds are too fast I get an infinite loop error and the program won't run. I think it is the same things as what you are saying. Have you seen that before?
Application Engineer
Robotiq
[email protected]
I think Grady is right. Another possibility is that if the increment is too high, the robot will check for the force level between each motion only and therefore a high force can be induced if the the contact is with a rigid object. This high force may cause a "sudden stop".
Another way of implementing this would be the following:
- Insert a "if" with the option "expression checked continuously" select. The condition could be, for example, "if Fz >= -10".
- Inside the "if", place a relative move, for example a 10cm downward motion
- Make sure you have a "set zero" before the motion (or before the "if"), when there is no contact with the tool.
This will make sure that the robot moves until the force meets a certain threshold (in this case 10N upwards). You will need to increase the speed gradually as a high speed will make the real force exceed the threshold (the robot needs time to stop).
This alternative method works well when you need to move until a certain force is reached, but is not meant to control a force continuously.
Nicolas Lauzier, Eng., PhD
R&D Director
[email protected]
If you need any help around implementing this let me know and I can do a sample program
The one thing that I will say is that we have not deployed too many robots with the robotiq URCap, we mainly use the script functions since they seem to run faster for us for whatever reason. Maybe try using the script function rq_open_and_wait() instead of the program node from the URCap. I will be doing some testing in the next couple of days to actually quantify that position and will post the results here.
If you want to send over the program I can try to take a look at it as well more closely where I can click around and see if anything pops out at me or I am sure there are others on here as well that can also look at it if you don't mind it being on here in a public forum. If not you can email it to me at [email protected]
Glad you were able to get it running @bsawlor