Robotics Toolbox

Comment from Huub vN -- March 27, 2015, 04:12:24 PM    

After defining and plotting a manipulator, I try to use ikine3:

T_start1 = transl(1.75, 1.5, -1.5);
T_end1 = transl(1.5, 1.0, -1);
T_traj1 = ctraj(T_start1, T_end1, 50);
qi = ikine3(leg1, T_traj1,'rd');

but for some reason this ends with:

WARNING: RTS:ikine3:notreachable:   point not reachable
 !--error 15 
Submatrix incorrectly defined.
at line      75 of function ikine3 called by :  
qi = ikine3(leg1, T_traj1,'rd');

I don't believe the point is not reachable and when watching the inverse kinematics demo,
I can't figure out what I may be doing/thinking wrong. Any suggestions, if possible ?

Comment from Corrado Guarino Lo Bianco -- March 27, 2015, 04:33:21 PM    

Hi Huub,
difficult for me to say if the point is reachable or not: I have no idea of the robot you
are using and where it is located!

The code was taken by Corke from the following paper:

Paul and Zhang, "Computationally Efficient Kinematics for Manipulators with Spherical
Wrists Based on the Homogeneous Transformation Representation," The International
Journal
of Robotics Research, Vol. 5, No. 2, Summer 1986, p. 32-44.

You should give a look to the paper in order to understand the origin of your problem.

Comment from Huub vN -- March 27, 2015, 08:17:42 PM    

Hi Corrado,

Yes, I can understand it's difficult to say without more info.

Thanks for the paper. This explains where the demo example originates from.

Comment from Huub vN -- May 5, 2015, 11:13:11 AM    

Hi Corrado,

I'm trying to simulate my model using ikine3 and ikine6s. Neither work yet, but ikine6s
expects a manipulator with a spherical wrist, However, after studying the example that
uses the mdl_puma560 and looking at its data, I can't find an indication or setting for
the spherical wrist. Am I missing/overlooking something ?

Comment from Corrado Guarino Lo Bianco -- May 5, 2015, 11:39:48 AM    

The solution method provided by ikine3 and by ikine6s only works with a robot which has
the structure of a Puma 560 manipulator. You can assume longer or shorter arms, but the
the basic structure of the robot must be the same.
The spherical wrist is simply obtained through a proper choice of the kinematic parameters
of the last joints (roughly speaking by setting coefficients a_i and d_i of the last two
joints equal to zero).