How Servo motor functioning.

Any one tell me how servomotor functioing.i have AC.Servomotor.is any difference between AC servo and DC servomotor.Can we use induction motor instead of AC servomotor if not what is reason behind this.
Thanks,
Naeem Ahmed

There are many answers to your questions, but one of the most obvious answers is that

DC Motor Servo systems have VERY HIGH TORQUE/VELOCITY PROFILES.

This is the primary difference between the two.

you don't explain what kind of functionality you want to understand. AC or DC or hydraulic or whatever is just what powers the axis.

I would like to hear more about this also.

Servo has been defined for me as anything that has position feedback. This appears to be necessarily vague since it can nearly apply to anything.

In the case of linear actuators there would be some sensing that could vary from simple limit switches at each end of travel to very fine. Also would be some kind of controller ie valve etc whose precision of control would have to be proportional to the degree of position sensor precision.

Same kind of thinking wouuld apply to motors whether AC or DC. Sensors again could vary from simple ie limit switches to a encoder where the precision of movement could vary from coarse ie multiple motor revolutions to one or a fraction of a revolution.

The level of desired precision would dictate the motor and the controller selection.

Rough position control ie 1/4" for a carriage could be done with limit switches and almost any motor.

Very fine ie precise position control ie 0.001" would require very precise position sensing and very fine controller and a motor that allows for very fine control of shaft position ie synchronous (either a wound rotor or a rotor with magnets)

Dan Bentler

For me "servo" also implies active position maintainence at zero speed.

By "active position maintenance", do you mean that all servos are "stepper" motors and work on a "pulse count" control system?

By "active position maintenance", do you mean that all servos are "stepper" motors and work on a "pulse count" control system?

Click to expand...

I simply meant that a positioning system does not release control once in position. It monitors the feedback and provides correction if the desired point is changed by external forces. The method of applying correction is specific to each system. This is the more generic definition I use and could apply to a PID control of temperature as well as a positioning system (though PID is just a control algorithm).

I see your point now Bernie. I guess this is more what I was after: (copied from another site)

Stepper motors can lock into a fixed postion, while servo motors can not. It's that simple. A servo will compare the output (position converted to voltage) to the input (the desired position converted to voltage) and make them the same by changing the output. This is a balancing act. Any external event that changes the position of the motor will be corrected by an opposing torque produced from this balancing act. This correction takes time to settle. It will either be a slow position correction or a series of overshoots that will oscillate back and forth until a midpoint is found relatively quickly. Stepper motors have a much higher holding torque and will remain in a fixed position until overpowered. DC servo motors, however, have a higher torque *during rotation* than steppers and a much higher RPM. To match a stepper motor's holding torque, you would need an expensive high torque servo motor. Deciding wether to use a servo motor or stepper motor is based on the needed holding torque (steppers) versus torque while in motion (servo). And don't forget that servo motors have a higher RPM.

I mean someone explain its function through block diagrame.

what kind of difference in winding of AC servo and Stepper motor

http://en.wikipedia.org/wiki/Stepper_motor
http://en.wikipedia.org/wiki/Servo

Thanks panic more for link.