The Basis of Feedback Control
This class uses a CD player's pickup to explain focus servo with feedback control. Please find physical image of the servo!!
The following is an example of linear movement of the pickup.
The block diagram becomes like this after some calculation from specification of a pickup (See this in detail, sorry, in Japanese). "Fv" is a constant of Voltage-Force transform.
This block diagram tells you that it detects "position" and "velocity" then feedbacks them with constants "K/m" and "C/m". i.e. This pickup has servo-loop itself.
See the frequency response!!