The response curve of this system doesn't seem to change (at all) even when the load of the slider is increased while keeping the PID gains constant , Why is that ??

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Response Curve (not changing)- </matlabcentral/answers/uploaded_files/108759/Screenshot%20(54).png>

Changing mass of slider by changing the density of material- </matlabcentral/answers/uploaded_files/108760/Screenshot%20(53).png>

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I have added the model and a few screenshots here for reference. Please help me understand why the response curve ( actual position vs desired position ) to my given pulse input is not changing at all even when I'm changing my slider mass ( by modifying the body inertia properties of my 3D simscape slider block) while keeping the same PID gains to control it. My project is centered around improving the response and minimizing error due to the variation in the load acting on the slider, hence getting this part right is crucial and any help on this is greatly appreciated. P.S - Please don't worry about the extremely high values of density as I've modeled the slider at small dimensions and hence needed it to obtain realistic values of mass for analysis purpose.