[HuFlungDung]

Benny,
In an "intelligent system", not only does the controller have to issue a movement command, it also needs to receive verification that the position was reached as commanded. This is the so called servo "loop".

In a typical stepper system, the movement commands are issued, but no check is carried out to see if the movement succeeded in execution. This is "open loop".

In a servo system, the controller monitors the encoder position. There is logic built in that compares the current commanded position to the actual position of the encoder. As soon as there is a discrepancy, this generates an error signal in the controller. This error signal is amplified by the servo amps into a useful voltage and current to drive the servo motor. The motor turns, and all the while the controller is looking at the feedback from the encoder.

As the current encoder position is fed back and compared to the commanded position, the controller decreases the error signal, because the positional error is decreasing as the motor moves the machine. The servo amp also cuts back on the voltage applied to the motor. So an equilibrium is reached when the encoder shows zero error between the present and the commanded position. Then motion stops.

So if there is a large inertial load on the servo motor during the movement, the controller is still looking at the encoder feedback, the error signal still exists for as long as it takes for the encoder to reach the equilibrium position. If the motor turns, the encoder counts, and thus there is some "intelligence" to the circuit because the feedback loop is always reporting, and the motor will receive voltage until such time as the fuse blows, or it reaches position.