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I'm working on a pantograph device, which is not a linear plant, and implemented 2 different control schemes. First one is computed torque;
For this control technique, I modeled nonlinear terms in the equation of motion and canceled them by injecting their model within the control input, which is torque for two motors. This way I achieved a very fast response but since the controller was PD, there is always a steady state error, which gets smaller as the P gain increases though.
The second method was the classic PID method. Again I used PD controller for each motor and what I observed is a very slow response, like 3-5 seconds to catch the reference. Furthermore, the gains I used was extremely high even to be able to get this response, like Kp = 15000, Kd = 15000
My question is;
Is the reason why PD controller performs too slow, due to non-linear plant ?
And one more question for the Computed torque technique;
I used the following control input;
Torque = M(q)*[qd'' + Kv*e' + Kp*e] - H(q,u) - Bf(q)*Fext
Where H and Bf terms are the non-linear parts I cancel.
qd = desired joint angle;
qactual = actual joint angle;
e = qd-qactual
e' = derivative of error
qd'' = desired acceleration
M(q) = mass matrix
So, this model is the PD controller. Is it possible to build a PID controller with Computed torque technique ?
For this control technique, I modeled nonlinear terms in the equation of motion and canceled them by injecting their model within the control input, which is torque for two motors. This way I achieved a very fast response but since the controller was PD, there is always a steady state error, which gets smaller as the P gain increases though.
The second method was the classic PID method. Again I used PD controller for each motor and what I observed is a very slow response, like 3-5 seconds to catch the reference. Furthermore, the gains I used was extremely high even to be able to get this response, like Kp = 15000, Kd = 15000
My question is;
Is the reason why PD controller performs too slow, due to non-linear plant ?
And one more question for the Computed torque technique;
I used the following control input;
Torque = M(q)*[qd'' + Kv*e' + Kp*e] - H(q,u) - Bf(q)*Fext
Where H and Bf terms are the non-linear parts I cancel.
qd = desired joint angle;
qactual = actual joint angle;
e = qd-qactual
e' = derivative of error
qd'' = desired acceleration
M(q) = mass matrix
So, this model is the PD controller. Is it possible to build a PID controller with Computed torque technique ?