This function does not fully set the dimensions of output port 2 error in matlab?

hi. I simulated impedance control for ur10.but there is an error:

Error in default port dimensions function of S-function 'impedance2/impedance controller'. This function does not fully set the dimensions of output port 2

I guess it the problem is with x signal. x is 1 if this is wrong. the signal should be 6,1 in ur10forwardkinematic block. I don't know where is output port2 exactly and how can I fix this problem? The Simulink file is attached.

Answer 1

[Sebastian Castro]

Hi Najmeh Eskandari,

I would highly recommend running this code in MATLAB and debugging it yourself. I just did the same and your line 153 seems to have incorrect MATLAB code that causes an error.

C(k,j)= C(k,j)+0.5*(diff(D(k,j),q(i,1))+diff(D(i,k),q(j,1))-diff(D(i,j),q(k,1)))*dq(i,1);

Error using diff
Difference order N must be a positive integer scalar.

Try starting by fixing that. The second input to the diff function is actually just the number of differences to compute (so it should be an integer), but you are passing in values like q(j,1) and q(j,2) which are noninteger joint angle values, so this is incorrect.

https://www.mathworks.com/help/matlab/ref/diff.html

- Sebastian

[Najmeh Eskandari]

yes you are right and I knew the error relates to C matrix so I calculated C in mfile and I wanted to use it in Simulink to fix this error but it is too long (ur10C.txt) and in symbolic form and I don't know how to import it to Simulink(from file block did not work for symbolic data)

[Najmeh Eskandari]

-diff(D(k,j),q(I,1)) is D(k,j) derivative to q(I,1) variable while for example diff(D(k,j),2) is second order derivative of D(k,j).

[Sebastian Castro]

Hi Najmeh,

I wanted to clarify, the diff function does not calculate an analytical derivative with response to a variable -- rather, it approximates the numerical derivative of an array of values.

What you're basically trying to do is get the Jacobian of the robot dynamics at a specific configuration (set of angles), which you'd have to do in another way. You can either:

• Derive the Jacobian from symbolic equations using Symbolic Math Toolbox
• Use the Get Jacobian block from Robotics System Toolbox

If you said you already derived it symbolically, there is a matlabFunction function that will automatically generate MATLAB code from that "long, ugly expression".

https://www.mathworks.com/help/symbolic/matlabfunction.html

You can definitely use that inside a MATLAB Function block. I've done this recently for a simple 2DOF inverse kinematics calculation.

- Sebastian

[Najmeh Eskandari]

Thank you Sebastian.I'll try your suggestion.

Answer 2

[Nicolas Schmit]

Simulink is having a hard time determining the dimension of the outputs of the MATLAB Function blocks. The root cause is that you have many undefined variables in the code of the MATLAB function blocks. Because of those undefined variables, MATLAB cannot execute the code of the blocks and thus cannot determine the dimension of the outputs.