PTP Axis 6 limit with singularity

    Hello,

    I have a KRC2 6 axis robot for stacking. It grips a part, turns it 180degrees and stacks it. Because of poor preparation in tooling and positioning it has to move through singularity at a certain height of the stack. with the combination of some LIN movements and turning axis 5 it works but it is ofcourse not very smooth.

    When I try to use PTP movements due to the variation in the base height the robot sometimes wants to overturn axis 6. This ofcourse throws an error: "axis 6 out off limits" even though the position is reachable when he does a LIN movement.

    I prefer to use PTP movements because off the speed and smooth motion, there is also enough space to let the robot move. Another way of solving this is ofcourse to make a fix position depending on the stack height which always works but again it is cleaner if the turn position changes with the stack height.

    and your question is?

    if you want an answer to your problem you already gave it yourself:

    Quote from Joeri

    Because of poor preparation in tooling and positioning it has to move through singularity at a certain height of the stack

    but is suspect that is not the answer you are looking for :winking_face:

    if you question is why does LIN moves work where PTP fail. that is pretty simple. with LIN moves you force the arm past the singularity (at a reduced speed so A4 and A6 don't overspeed)

    With PTP moves this can become a bit trickier depending on how you program it. For PTP moves status and turn are used to determine in what orientation the arm ends up. How are you programming your robot? with inline forms or straight KRL?

    Every problem has a solution, that isn't the problem. The problem is the solution.

    I am programming with inline forms.

    My goal is to make it move smoother and quicker, PTP movements would do this but I am struggling on how to use them around the singularity without overturning axis 6.

    is there a way to lock the configuration of axis 6 or is there a better way to work around this problem. I want to learn on how to do this better if i ever come across this problem again.

    Quote from Joeri

    My goal is to make it move smoother and quicker, PTP movements would do this but I am struggling on how to use them around the singularity without overturning axis 6.

    PTP moves have no singularities, since they move robot in axis space and not in cartesian space. There must be a misinterpretation on your side. The only problem where singularities can be an issue is if start or end position of the PTPare given that are inside a singularity because given Cartesian start and/or end position need to be transformed into axis space to get the corresponding axis start and/or end values. There is an option that prohibits teaching position inside singularities so this problem can be avoided when teaching. I do not remember the system variable for this but i am pretty sure its documented inside this forum.

    How the robot moves for PTP is solely defined by Status and Turn bits. If your issue is an axis limitation it definitly is a turn issue. If it is a workspace error it is a status issue. Read about Status and Turn and Cartesian position ambiguities in the system Integrators manual. This can be solved by using INVERSE to do some pre calculations and calculate the fitting turn for your movement before hand. Examples for this can be found inside the forum. Unfortunately this requires skills in plain KRL programming.

    it has been years since i have used inline forms, but they should save each position with the status and turn information.

    Simplest solution is add more points where the singularity is. Basically tell the robot more exactly how to navigate it best. this way it should not "flip a6" in its final position

    there are probably better solutions but without seeing the actual movement that is going to be hard to recommend something. best would be to either avoid or at the least increase the distance to the singularity.

    Quote from Joeri

    is there a way to lock the configuration of axis 6 or is there a better way to work around this problem. I want to learn on how to do this better if i ever come across this problem again.

    not while using PTP moves. PTP moves from point A to point B in the fastest way possible. With LIN and CIRC moves there are options because they are path orientated. Depending on your KSS version you also have access to spline motions, that also has some options.

    Every problem has a solution, that isn't the problem. The problem is the solution.

    Thank you for the responses it did put me on the right way.

    the problem was that indeed the T and S values did not match the configuration anymore on certain heights. LIN movements ignore this and do make it reachable without triggering a fault.

    turning through the singularity point I solved using points with axis values.

    thank you all for the comments and help!

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