Can I do a kinematics redundancy by using inverse kinematics?

Question

Ranatchai Laosiripong 2020-12-9

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/689034-can-i-do-a-kinematics-redundancy-by-using-inverse-kinematics

评论： Yiping Liu 2020-12-17

在 MATLAB Online 中打开

Are there any ways to do Inverse kinematic and get something like this?

https://www.youtube.com/watch?v=sZYBC8Lrmdo&ab_channel=KUKA-Robots%26Automation

what constrait do I need to add?

I tried to do something like this, but it doesn't well succeed

lbr = importrobot('iiwa14.urdf'); 
lbr.DataFormat = 'row';
initialguess = lbr.homeConfiguration;
gripper = 'iiwa_link_ee_kuka';
link1 = 'iiwa_link_1';
count = 1;
gik = generalizedInverseKinematics('RigidBodyTree',lbr,'ConstraintInputs',{'pose','orientation','joint'});
poseConst = constraintPoseTarget(gripper);
poseConst.TargetTransform = trvec2tform([0.5 0.5 0.4])*eul2tform([0 0 -pi]);
jointConst = constraintJointBounds(lbr);
maxJointChange = deg2rad(10);
orientationConst = constraintOrientationTarget(link1);
min = -70;
max = 70;
for i = min:10:max
   if i == min
       jointConst.Weights = zeros(size(jointConst.Weights));
       orientationConst.TargetOrientation = eul2quat([deg2rad(i) 0 0]);
       qs(count,:) = gik(initialguess,poseConst,orientationConst,jointConst);
       initialguess = qs(count,:);
       count = count+1;
   else
       jointConst.Weights = ones(size(jointConst.Weights))*0.25;
       jointConst.Bounds = [qs(count-1,:)' - maxJointChange, qs(count-1,:)' + maxJointChange];
       
       orientationConst.TargetOrientation = eul2quat([deg2rad(i) 0 0]);
       orientation.Weights = ones(size(orientationConst.Weights))*0.25;
       
       qs(count,:) = gik(initialguess,poseConst,orientationConst,jointConst);
       initialguess = qs(count,:);
       count = count+1;
   end
end
framesPerSecond = 5;
r = rateControl(framesPerSecond);
for i = 1:count-1
    show(lbr,qs(i,:),'PreservePlot',false);
%     show(lbr,qs(i,:));
    drawnow
    waitfor(r);
end

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Answer 1

Yiping Liu 2020-12-10

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/689034-can-i-do-a-kinematics-redundancy-by-using-inverse-kinematics#answer_570999

在 MATLAB Online 中打开

You sould not use orientationTarget for link1.

Try something like below (You only need pose and joint constraints)

lbr = importrobot('iiwa14.urdf'); 
lbr.DataFormat = 'row';
initialguess = lbr.homeConfiguration;
gripper = 'iiwa_link_ee_kuka';
link1 = 'iiwa_link_1';
count = 1;
gik = generalizedInverseKinematics('RigidBodyTree',lbr,'ConstraintInputs',{'pose','joint'});
poseConst = constraintPoseTarget(gripper);
poseConst.TargetTransform = trvec2tform([0.5 0.5 0.4])*eul2tform([0 0 -pi]);
jointConst = constraintJointBounds(lbr);
maxJointChange = deg2rad(10);
min = -70;
max = 70;
for i = min:5:max
   if i == min
       
       qs(count,:) = gik(initialguess,poseConst,jointConst);
       initialguess = qs(count,:);
       count = count+1;
   else
       bounds = jointConst.Bounds;
       bounds(1,:) = [initialguess(1) + 0.025, bounds(1,2)];
       jointConst.Bounds = bounds;
       
       qs(count,:) = gik(initialguess,poseConst,jointConst);
       initialguess = qs(count,:);
       count = count+1;
   end
end
for i = 1:count-1
    if i == 1
        ax = show(lbr,qs(i,:),'PreservePlot',false);
        view(ax, 80, 36);
    else
        show(lbr,qs(i,:),'PreservePlot',false, 'Parent', ax);
    end
    drawnow
    hold on
end

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Yiping Liu 2020-12-15

编辑：Yiping Liu 2020-12-15

在 MATLAB Online 中打开

I got the same qs when I run the script above, and you can try to visualize that, it should look pretty smooth.

>> qs
qs =
4331    0.9973    0.8355   -0.9656   -0.6823    1.4155   -2.0431
4581    0.9758    0.7628   -0.9656   -0.6200    1.3964   -2.0684
4831    0.9575    0.6943   -0.9656   -0.5620    1.3803   -2.0929
5081    0.9416    0.6290   -0.9656   -0.5073    1.3665   -2.1166
5331    0.9280    0.5663   -0.9656   -0.4552    1.3547   -2.1398
5581    0.9161    0.5056   -0.9656   -0.4052    1.3445   -2.1624
5831    0.9059    0.4465   -0.9656   -0.3570    1.3358   -2.1847
6081    0.8972    0.3887   -0.9656   -0.3101    1.3285   -2.2066
6331    0.8899    0.3321   -0.9656   -0.2644    1.3223   -2.2282
6581    0.8838    0.2763   -0.9656   -0.2196    1.3172   -2.2496
6831    0.8789    0.2212   -0.9656   -0.1756    1.3131   -2.2707
7081    0.8751    0.1667   -0.9656   -0.1322    1.3099   -2.2918
7331    0.8724    0.1125   -0.9656   -0.0892    1.3077   -2.3127
7581    0.8708    0.0586   -0.9656   -0.0464    1.3063   -2.3335
7831    0.8702    0.0048   -0.9656   -0.0038    1.3058   -2.3543
8081    0.8706   -0.0489   -0.9656    0.0387    1.3061   -2.3751
8331    0.8721   -0.1028   -0.9656    0.0814    1.3074   -2.3959
8581    0.8746   -0.1569   -0.9656    0.1244    1.3094   -2.4168
8831    0.8782   -0.2113   -0.9656    0.1678    1.3124   -2.4378
9081    0.8828   -0.2663   -0.9656    0.2117    1.3164   -2.4590
9331    0.8887   -0.3220   -0.9656    0.2563    1.3213   -2.4803
9581    0.8958   -0.3785   -0.9656    0.3018    1.3273   -2.5019
9831    0.9043   -0.4360   -0.9656    0.3484    1.3344   -2.5237
0081    0.9142   -0.4948   -0.9656    0.3964    1.3429   -2.5459
0331    0.9257   -0.5552   -0.9656    0.4460    1.3527   -2.5685
0581    0.9390   -0.6175   -0.9656    0.4977    1.3642   -2.5916
0831    0.9545   -0.6823   -0.9656    0.5519    1.3776   -2.6152
1081    0.9723   -0.7502   -0.9656    0.6093    1.3933   -2.6395
1331    0.9932   -0.8220   -0.9656    0.6707    1.4118   -2.6647

If you check the solver parameter,

>> gik.SolverParameters
ans = 
  struct with fields:
         MaxIterations: 1500
               MaxTime: 10
     GradientTolerance: 1.0000e-07
     SolutionTolerance: 1.0000e-06
    EnforceJointLimits: 1
    AllowRandomRestart: 1
         StepTolerance: 1.0000e-14

You can see the AllowRandomRestart is turned on by default. You can turn it off - that will guarantee repeatable results, however, in this case, for the given problem, the solver should always be able to comfortably find a solution before it needs to do a random restart.

Which version of MATLAB do you use?

Ranatchai Laosiripong 2020-12-17

Your qs is running quite smooth like you said.

I use 2020b version. It's really weird that I get different result from you.

Yiping Liu 2020-12-17

I just tested the script in 2020b release and I get exactly the same result shown above. Maybe some internal files in your MATLAB installation got corrupted? I would suggest you start a tech support case regarding this issue.

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