Alex Joni wrote:
>>> <...>
>>> Yes, EMC2 definitely can do this. There is a general robot kinematics
>>> file. You have to
>>> measure the length of the arms between joints and put that into the
>>> program, so the transform
>>> matrices are built correctly. You also have to establish the alignment
>>> to each joint's home position.
>>> In EMC's sample-configs directory, you will find a puma sub-directory.
>>> It calls in the kinematics file "pumakins".
>>>
>>> Jon
>>>
>>>
>>>
>> Oooh, I'm wetting my pants! My idea is closer to working than I thought.
>> :)
>>
>
> Right, it has been done before with some sort of results.[1]
>
> Actually there are a couple kinematics calculations included with emc2.
> For serial robots and for parallel kinematics.
> For serial robots based on the type there are:
> * scarakins - for SCARA type robots [2]
> * pumakins - kinematics file for a Unimate PUMA (antorpomorphic robot). I
> worked a while with these calculations, but I couldn't completely figure out
> the exact type of the robot (unimate had a couple puma's, with left and
> right arm configurations). There is a vismach simulation for pumakins, but
> it doesn't work 100% (straight XYZ lines aren't quite straight).
> * genserkins - general serial kinematics: kinematic calculation for any
> serial (max. 7 DOF) robot[3]. These functions are suitable for any type of
> industrial robot (which isn't a parallel kins). The kins support (although
> minor tweaks are needed) rotary and prismatic joints, so you only need to
> have a drawing of your robot, and you can use them.
> There is a small problem, that the kins sometimes don't converge.. but I
> haven't looked into that yet.
> I created a new puma configuration, based on genserkins, and the puma
> dimentions of Sam Sokolik's robot.
> I then did a 3D model of his puma, and created a vismach model from that.
> Once that was set up, I could run a regular g-code program and check if the
> result is ok. As you can see from the screenshots [4], the results are dead
> on. So the kins are working 100% accurate (when they are working ;).
>
> After the good news, there's time for the bad news ;)
> The kins (genserkins mostly) are working most of the time. There are some
> glitches when they don't (not sure yet why), but that made me realize emc2's
> motion controller currently doesn't really handle cases when kins aren't
> working. It's probably a non-recoverable error, but it should enter estop,
> stop what it's doing etc. Currently motion is hanging, so that means bigger
> problems. I would advise to test genserkins on simulated machines, until
> confident it works ok.
> The emc2 code (some part inherited from EMC1) suffers from mixup of axes and
> joints. There is ongoing work to clean this out, but it's still pretty far
> from beeing useable. This means that in some places things are mixed up.
> emc2 takes axes settings from the ini, but sets them as the joint limits
> (step generator) but not as the trajectory's joint-command outputs. In traj
> the limits are wrongly enforced as carthesian limits on the axes.
> This means it's quite some work to get a good config working (probably some
> hacking involved).
>
> Regards,
> Alex
>
>
> [1] - http://www.youtube.com/watch?v=TLxwAX8G3oI
> [1] - http://www.youtube.com/watch?v=AoOWi1r6-Eo
> [2] - http://en.wikipedia.org/wiki/SCARA
> [3] - http://en.wikipedia.org/wiki/Serial_manipulator
> [4] - http://juve.ro/blog/puma
>
>
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Very informative post Alex, thanks,
Do these problems occur with the Hexapod kins ? I've been reluctant
to build one
because any faults with the control software could start bending things,
as the actuators
would be fighting each other.
Glen.
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