SCARA hand region issues

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22 May 2017 13:31 #93475 by Niko
Hi all ,
I just put together the control for an epson scara arm .
After tuning the servos and home procedure in MDI I can't move past a point .
The arm is not physically limited in any way , there's plenty of travel , but it wont go past that point .
I raised the max and min travel to very large numbers and the problem persists .
Axis returns following error on all the joints involved in the move . That is joint 0, 1 and 3 .

Looking forward to any ideas .

Cheers

Nikolai

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22 May 2017 15:06 #93481 by andypugh
Replied by andypugh on topic SCARA hand region issues
Which version of LinuxCNC?

The axis limits are rectangular, but the joint limits are not. Perhaps this is the problem?

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22 May 2017 16:29 #93486 by Niko
Replied by Niko on topic SCARA hand region issues
I'll check the version tomorrow . Should be 2.7.8
So max limit and min limit correspond to X Y Z limits and not joint limits ?
The joints are set as angular so I expected them to be degrees of freedom .

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22 May 2017 20:15 #93503 by andypugh
Replied by andypugh on topic SCARA hand region issues

I'll check the version tomorrow . Should be 2.7.8
So max limit and min limit correspond to X Y Z limits and not joint limits ?


I am not sure with 2.7.8. With 2.8 there are separate limits for both joints and axes (but the axis limits are still a cuboid)

The joints are set as angular so I expected them to be degrees of freedom .

That's probably right. Did you check for any limits applied in the kinematics?

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23 May 2017 06:48 #93518 by Niko
Replied by Niko on topic SCARA hand region issues
It's 2.7.0 .
Where can I get 2.8 from ?
Max and min limit in INI are set to more than a meter (twice the length of the arm).
Where can I check the limits in the kinematics ?
Other than hal and ini I'm pretty clueless .

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23 May 2017 12:12 #93523 by andypugh
Replied by andypugh on topic SCARA hand region issues

It's 2.7.0

You should update to 2.7.8, though it won't help here.

Where can I get 2.8 from ?

Currently from buildbot.linuxcnc.org, though it might not help with your problem it will give you a system better-suited to robots.

Where can I check the limits in the kinematics ?
Other than hal and ini I'm pretty clueless .

That would be in the scarkins code:
github.com/LinuxCNC/linuxcnc/blob/master...nematics/scarakins.c
Possibly the acos in the inverse kins always returns an angle < 90?

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24 May 2017 06:11 - 24 May 2017 07:39 #93578 by Niko
Replied by Niko on topic SCARA hand region issues
Upgraded to 2.8 .
It works but in a rather weird fashion . As a joint Z works fine but when I switch to real world position it switches direction .

Is there any logic to debugging nonlinearity in straight moves ?
I've already checked the lengths and encoder count rates and still get a slight curve .

P.S. in MDI linear moves on x or y result in "linear move on line 0 would exceed joint z positive limit".

And the point which limits it is at 90 degrees between arms .
Last edit: 24 May 2017 07:39 by Niko.

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24 May 2017 12:18 #93591 by andypugh
Replied by andypugh on topic SCARA hand region issues
I am a bit surprised that you have a "joint" called "Z". Do you mean Joint 3?

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25 May 2017 08:24 #93604 by Niko
Replied by Niko on topic SCARA hand region issues
Joints and axes are fine . Right now I'm wondering how to recompile stuff .

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25 May 2017 09:50 #93605 by andypugh
Replied by andypugh on topic SCARA hand region issues
For a simple kinematics module you might well be able to use halcompile. It's certainly worth a try.

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