What is a servo system?

A servo system is an electro mechanical or hydraulic system that can follow a desired position, speed or time in a closed loop fashion.  A servo system consists of a motive apparatus, a feedback sensor and and logic, usually electronic but can be mechanical, that commands the motive apparatus to a desired set point.  For example, In the case of a electric motor with an encoder and a motion controller, the servo loop creates a desired set point or even a motion profile, and the motion controller takes the position information from the encoder and compares it to the desired set point.  If the desired and actual position is the same, it does nothing.  If it is not, it drives the motor until it's position matches the the desired posiiton. The algorithim most commonly used is the PID (see http://en.wikipedia.org/wiki/PID_controller)

A servo system is a control system that converts a small mechanical motion into something that requires much greater power. This transfer can be achieved by using many different electro mechanical devices such as servo motors and servo valves. If you are interested in any further information on servo systems, check out the learning center at http://www.repairzone.com/learningcenter/home?kmas=328, which has articles and videos on servo system components.