I'm currently taking classical control theory and have some questions regarding basic concepts related to closed loop systems.
Let's say I have a simple servo motor controlled by an electric current. Using a PID controller, my block diagram is as follows:
Now, I'm still struggling to understand some things:
- At what point is my loop actually producing a signal that my servo can use? And how would I extract it from my control loop?
- Why can I simply take my PID'ed error signal and plug it into a plant requiring current as an input? If I had a set current I could calculate the torque on my motor, from which I could then determine the accerleration and thus get the position by integrating that value twice. How do I do such a calculation if I only have a value that tells me to either increase or decrease my current by some factor?
- Why is the positional output calculated by my plant reconnected to my sensor in the feedback loop? Why is there an output in the first place? Shouldn't the sensor simply deliver continous data and the loop respond according to my error term?
I would be very glad if somebody could answer these basics questions for me, I just can't quiet wrap my head around the basic mechanics of a control loop like this.
Thanks in advance!