Genserkins: how to set the desired joint position?

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28 May 2019 15:14 #135174 by Cornflakes
Hi!

I use G code to position my 6DOF robot arm.
I use LCNC 2.8 and genserkins.

Sometimes the robot correctly gets to the given coordinates by command G0
But sometimes it tries to go to desired coordinates in other joints positions than I expected
As a result, it may go beyond limits or even stop due to kinematics error

How can i tell to trajectory planner (or something else) what positions of joints i need?
How does the trajectory planner choose specific positions of joints from several possible options?

Thanks!

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28 May 2019 22:57 #135218 by andypugh

Cornflakes wrote: How can i tell to trajectory planner (or something else) what positions of joints i need?
How does the trajectory planner choose specific positions of joints from several possible options?


It is Genserkins which chooses the pose of the machine to achieve a position.

I don't know if genserkins is clever enough to avoid joint lock if it happens to choose (for example) elbow-down in a situation where elbow-up would be better.

Basically genserkins just throws matrix maths at the problem and will accept any solution that is valid for the current position without considering where it can get to from that position.

I don't know if Pumakins is any cleverer.

I am playing around with serial kins myself at the moment, with a measuring arm, and I am learning a lot :-)
It's a complicated field.

Looking at genserkins, I do see that it has an "unrotate" pin, but I actually have no idea if that is relevant or helpful.

github.com/LinuxCNC/linuxcnc/blob/master...cs/genserkins.c#L604

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