Encoder Query

[bean7795]

Alright my genius brothers could any one explain in idiot terms the principle of an encoder and could a servo be made out of a stepper with the aid of an encoder

[Al_The_Man]

I will take a crack.. Actually you don't need an encoder to create a 'servo' . Originally a servo resembled a stepper motor or more exactly a resolver, which has an energized winding and two output windings with an angular displacement as regards output.
where two identical devices were hooked up and when the primary device was rotated the secondary device would faithfully follow the first, this had uses as in Radio antenna rotaters etc. In some cases the output was amplified so a larger recieve unit could be used.
But today the servo comes to mean any device that faithfully follows an input command and can be an open loop, like a stepper or closed loop like a DC or AC motor with some kind of encoder attached, and the reason for the encoder is to provide feedback to the control system to indicate the exact position of the motor, whatever the type maybe. So to sum up adding an encoder to a stepper is just a way of confirming that the stepper motor actually rotated the degree of steps it was fed.
If you want a detailed description of an encoder, absolute or incremental, you should find plenty by search.
Al.

[ger21]

An encoder just keeps track of where the motor is. A servo needs an encoder, because you can't just tell a servo to move a certain distance. It moves while power is applied to it. When the encoder tells the drive or controller that the servo has moved to where it's supposed to be, power is removed from the motor. If the encoder detects the motor moving when it shouldn't be, the drive will apply power to move it back to where it was.

A stepper, on the other hand, doesn't just spin. It moves in discrete steps which are sent from the drive. No encoder is needed, because you can tell a stepperr to move a certain distance and it can. There are closed loop stepper systems that use encoders to make sure the stepper actually moves to where it is supposed to. But this does not make it the same as a servo.
Steppers lose torque as rpm's increase. Servos do not.

I see Al is here, and he'll probably give you a better answer. Oops, he already did.