6DOF robot Limit Issues

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2 years 2 weeks ago #312013 by Project_Hopeless
I have a hobby robot partly based on the Melfa sim.  When I home the robot all axis report zero degrees.  The Cartesian location appears correct and it jogs correctly in world/Cartesian. The problem is I'm getting axis limits that contradict what is reported at the Home position pictured below. 

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With axis 2 limit set to -45/+110 I'm getting a error at -20 degrees.  It appears the axis limits are rotated 90 degress some how.  Is there an absolute vs. relative setting?  

 

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I could fudge the limit settings but I want it done right.  How should I define the axis limits?

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2 years 2 weeks ago #312038 by Aciera
Replied by Aciera on topic 6DOF robot Limit Issues
You have a work offset of -90 set for Y (joint1) so your position is actually indeed -110.

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2 years 2 weeks ago #312112 by Project_Hopeless
Do I need to have the axis offsets loaded?  In the 429remap.ngc G10 is loading axis offsets.  Is it necessary for either genserkins or idenity kins?
Code:
   M66  E0 L0                           ; force synch    M68  E#<SWITCHKINS_PIN> Q#<kinstype> ; set kinstype value    G10 L2 P8 X0 Y-90 Z0 A0 B90 C0    G59.2    M66  E0 L0                           ; force synch

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2 years 2 weeks ago #312133 by Aciera
Replied by Aciera on topic 6DOF robot Limit Issues
You don't _need_ it, those are simply used to define the pose for (x,y,z,a,b,c)=(0,0,0,0,0,0).

[edit]

Actually I just noticed that you are not getting an 'axis' limit error but a 'joint' limit error. So the issue is that you have to adjust your 'MIN_LIMIT' , 'MAX_LIMIT' values in the [JOINT_1] section of your ini file. Note that joint1=0 has the upper arm in the horizontal forward pose as that is what is used in the genserkins model so you may need to adjust the limit values accordingly.

www.linuxcnc.org/docs/2.9/html/sv/motion/dh-parameters.html

 

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2 years 2 weeks ago #312205 by Project_Hopeless

Aciera post=312133 userid=25994You don't _need_ it, those are simply used to define the pose for (x,y,z,a,b,c)=(0,0,0,0,0,0).

[edit]

Actually I just noticed that you are not getting an 'axis' limit error but a 'joint' limit error. So the issue is that you have to adjust your 'MIN_LIMIT' , 'MAX_LIMIT' values in the [JOINT_1] section of your ini file. Note that joint1=0 has the upper arm in the horizontal forward pose as that is what is used in the genserkins model so you may need to adjust the limit values accordingly.
 

So the joint axis limits in this case are relative the arm posture defined by the modified DH parameters?

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2 years 2 weeks ago #312223 by Aciera
Replied by Aciera on topic 6DOF robot Limit Issues
Yes

You can watch the current commanded joint position in the 'halshow' tool under:
'joint.N.motor-pos-cmd'
Where 'N' denotes the joint number (ie 1 for the joint in question).

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