Problems with Analytical Inverse Kinematics, no valid kinematic group found

Hi everyone,

I am trying to apply the "analyticalInverseKinematics " to a robot that I assembled. I tried to follow the matlab documentation instructions although with little success.

As you can see, the problem is that no valid kinematic groups are found. What am I doing wrong?

Thanks in advance.

clear;close all;clc



%-----------------
% END-EFFECTOR   |
%-----------------

% EE Coordinates      % Base coordinates
x_EE = 9;             x_0 = 0; 
y_EE = 8;             y_0 = 0;  
z_EE = 3;             z_0 = 0;

% Angles (Euler)
ang_EE = [-6*pi/5 -3*pi/4 pi/6];

% Pose
d_0EE = [x_EE - x_0, y_EE - y_0, z_EE - z_0];
H_0EE = trvec2tform(d_0EE)*eul2tform(ang_EE, 'ZYX');



%-------------------
% ROBOT STRUCTURE  |
%-------------------

% Structure initializing
robot = rigidBodyTree('MaxNumBodies',7);

% Links 
% Lengths         % Bodies 
l_1  = 2.5;       link_1  = rigidBody('link1');
l_2  = 5;         link_2  = rigidBody('link2');
l_3  = 5;         link_3  = rigidBody('link3');
l_4  = 3.5;       link_4  = rigidBody('link4');
l_5  = 1.5;       link_5  = rigidBody('link5');
l_6  = 1.5;       link_6  = rigidBody('link6');
l_EE = 1;         link_EE = rigidBody('linkEE');

% Joints
jnt_0 = rigidBodyJoint('joint_0', 'revolute');
jnt_1 = rigidBodyJoint('joint_1', 'revolute');
jnt_2 = rigidBodyJoint('joint_2', 'revolute');
jnt_3 = rigidBodyJoint('joint_3', 'revolute');
jnt_4 = rigidBodyJoint('joint_4', 'revolute');
jnt_5 = rigidBodyJoint('joint_5', 'revolute');
jnt_6 = rigidBodyJoint('joint_6', 'revolute');

% Home configuration
setFixedTransform(jnt_0, trvec2tform([0 0 0]));
setFixedTransform(jnt_1, trvec2tform([0 0 l_1]));
setFixedTransform(jnt_2, trvec2tform([l_2 0 0]));
setFixedTransform(jnt_3, trvec2tform([0 0 -l_3]));
setFixedTransform(jnt_4, trvec2tform([l_4 0 0]));
setFixedTransform(jnt_5, trvec2tform([l_5 0 0]));
setFixedTransform(jnt_6, trvec2tform([l_6 0 0]));

% Robot assembly 
link_1.Joint  = jnt_0;
link_2.Joint  = jnt_1;
link_3.Joint  = jnt_2;
link_4.Joint  = jnt_3;
link_5.Joint  = jnt_4;
link_6.Joint  = jnt_5;
link_EE.Joint = jnt_6;

addBody(robot, link_1, 'base');
addBody(robot, link_2, 'link1');
addBody(robot, link_3, 'link2');
addBody(robot, link_4, 'link3');
addBody(robot, link_5, 'link4');
addBody(robot, link_6, 'link5');
addBody(robot, link_EE, 'link6');

show(robot);showdetails(robot)



%----------------------
% INVERSE KINEMATICS  |
%----------------------

ee_coord  = d_0EE;
ee_pose   = H_0EE;
aik       = analyticalInverseKinematics(robot);
opts      = showdetails(aik)
aik.KinematicGroup = opts(1).KinematicGroup;
disp(aik.KinematicGroup)
generateIKFunction(aik,'robotIK');
ik_config = robotIK(ee_pose);



%----------------------------
% GRAPHICAL REPRESENTATION  |
%----------------------------

show(robot, ik_config(1,:));
hold on
plotTransforms(ee_coord, ee_pose)
hold off
figure;
num_sol = size(ik_config, 1);

for i = 1:size(ik_config, 1)
    subplot(1, num_sol,i)
    show(robot, ik_config(i,:));
end

Answer 1

[Varun]

Hi,

I understand you are trying to apply the "analyticalInverseKinematics " to the assembled robot but you get an error, no valid kinematic groups are found.

You can refer to similar question that got answered on MATLAB Answers: https://in.mathworks.com/matlabcentral/answers/688879-no-valid-kinematic-groups-were-found?s_tid=srchtitle