Explain AC vs DC Servo Motors

[tintruder]

Can anybody explain the difference between AC and DC Servo motors?

When I look at the vendors of drivers, it appears that the same drivers for 3-phase AC Servo Motors also support single-phase DC Servos and that the AC Drivers actually output a DC Bus voltage, not really AC.

For instance, http://www.aerotech.com/products/amps/amplifiers.html shows the BA series of drivers to do exactly this.

I bought some of the 400W Sanyo Denki AC Servos from Surplus Center and don't really know how to tell what sort of driver they need. I am hoping the driver design project in this forum category will yield results, but I am still very short of information.

Also wondering if any of the inexpensive/shareware CNC control applications that give step and direction commands for many stepper systems are usable in the servo world? Do any of these apps allow the encoder feedback or would I have to upgrade to some different package? If so, what packages exist that a hobbyist might be interested in?

Thanks much,

Tom

[H500]

The quick answer is that dc servos typically consist of a single coil that need to be energized with dc to make it turn.

Ac servos consist of several coils (phases) that need to be energized with sine waves having very specific timing relationships.

The low cost servo drives emulate a stepper driver, so they are compatible with programs like mach and turbocnc.

The driver takes care of the encoder feedback. The cnc program simply think its controlling steppers.

[Al_The_Man]

Originally Posted by tintruder Can anybody explain the difference between AC and DC Servo motors? When I look at the vendors of drivers, it appears that the same drivers for 3-phase AC Servo Motors also support single-phase DC Servos and that the AC Drivers actually output a DC Bus voltage, not really AC.

I think you are refering here to the fact that most DC Brushless amps, the motors of which resemble AC servo's, will also drive a DC brushed motor, They both however use PWM switching so it a high frequency switched DC voltage.
The DC Brushless motor and the AC servo motor appear identical, but the latter is controlled by a sine wave type voltage.
Al.

[unterhaus]

The controls that will do both brushed and brushless motors have controls that will recognize the lack of commutation signals and do the right thing. I think I even have some MTS drives that are made to do commutation with a resolver that can handle brushed motors. Most drives made in the last 20 years have a microcontroller on them, thus it's trivial to have this functionality if the manufacturer wants to go through the expense and bother.