I'm working on a pantograph device, which is not a linear plant, and implemented 2 different control schemes. First one is computed torque;(adsbygoogle = window.adsbygoogle || []).push({});

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 ?

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# Computed Torque Control vs. PID

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