You don't have any damper in your system, I tried this mathematically and gives me the same result (Oscillation). You must add damper if you want your system to stay at a specific position.
Here is the mathematical model for your system with and without damper.
>> n = [1] ;
>> d = [1 0 1];
>> fn = tf(n,d)
fn =
1
-------
s^2 + 1
Continuous-time transfer function.
>> t = 0:0.1:10;
>> wref = zeros(1,length(t));
>> wref(1:length(t)) = 1;
>> [y,t] = lsim(wref,fn,t);
>> plot(t,y)
After adding damper
d = [1 1 1]; % rest of the code remain the same
Here is the modified Simscape model (Damper value is kept 1,rest of the parameters are exactly the same as provided by you)
