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Inverse Kinematic Solver solutions

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Hello, I am using the robotic toolbox inverse kinematic solver as shown below.
My main question is why do I get different results everytime this script is ran? There are small differneces in the outputs but then every few iterations the values seem to almost double.
Thank you for any advice you can offer!
robot = importrobot('appleRobot.urdf');
homeConfig = robot.homeConfiguration;
ik = robotics.InverseKinematics('RigidBodyTree', robot);
ik.SolverParameters.AllowRandomRestarts = true;
ik.SolverParameters.MaxIterations = 1500;
x = 24;
y = 25;
z = 26;
%inches to meters
x = x / 39.37; y = y / 39.37; z = z / 39.37;
pos = [x y z];
pose = eye(4);
pose(1:3, 4) = pos';
weights = [0.25 0.25 0.25 1 1 1];
[configSoln,solnInfo] = ik('end', pose, weights,...
dis = 0; theta = 0; phi = 0;
dis = configSoln(1).JointPosition;
theta = configSoln(2).JointPosition;
phi = configSoln(3).JointPosition;
[dis theta phi];


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Accepted Answer

Cam Salzberger
Cam Salzberger on 6 Sep 2019
Hello Kyle,
The inverse kinematics solver parameter AllowRandomRestarts is likely the culprit here. If you check the documentation:
AllowRandomRestarts — Indicator if random restarts are allowed. Random restarts are triggered when the algorithm approaches a solution that does not satisfy the constraints. A randomly generated initial guess is used. MaxIteration and MaxTime are still obeyed. By default, random restarts are enabled.
Since there is some randomness in the solver process, the results may differ every time. Especially if there are multiple solutions for the same position.


Kyle Lammers
Kyle Lammers on 11 Sep 2019
Thank you for the response, its solved the issue of huge jumps in solutions.
Mosen shk
Mosen shk on 13 Nov 2020
How did you turned "AllowRandomRestarts" disabled?
Cam Salzberger
Cam Salzberger on 13 Nov 2020
Mosen, if you check out the examples attached to the inverseKinematics documentation, this example shows precisely how to do this.
ik = inverseKinematics('RigidBodyTree', pr2);
ik.SolverParameters.AllowRandomRestart = false;

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