How to convert polynomial trajectory block out to a 4×4 homogeneous transformation matrix

I created 7 waypoints using inverse kinematics designer app and exported the configuration into a matrix (7×6 matrix) containg xyz position and respective euler angles. From this matrix i input only the xyz position data(3×7 matrix) as waypoints to a polynomial trajectory block with time. But when i run the simulink an error is showing up, saying that polynomial trajectory output should be 4x4 homogeneous matrix inorder to connect to the inverse kinematics block input (pose). How could I resolve this issue

Answer 1

[Zinea]

Hi @Kannan,

The documentation of "Inverse Kinematics" block specifies that it expects a 4x4 homogeneous transform as input, which is the cause of the error. You can refer the documentation link given below:

https://www.mathworks.com/help/robotics/ref/inversekinematics.html

To resolve the error as stated in the question, you need to follow these steps:

1) Create a function that converts XYZ positions into 4x4 homogeneous matrices.

function H = xyz2homogeneous(xyz)
    H = eye(4);  % Create 4x4 identity matrix
    H(1:3,4) = xyz(:);  % Set translation component
end

2) Add a "MATLAB Function" block after your "Polynomial Trajectory" block with the following code inside it:

function H = fcn(xyz)
    H = eye(4);
    H(1:3,4) = xyz;
    H(1:3,1:3) = eye(3);  % Identity rotation matrix
end

In this way you can get the correct 4x4 matrix format for the "Inverse Kinematics" block, while using the existing XYZ trajectory generation.

Best!

[Kannan]

Thank you Zinea