need information about AC servo systems

Wow! What a question. To answer those requires a university degree. I suggest a library and 6 mos. of research as a start. Steve

maybe i didn't explain myself... i'm an electronice engineer with specialization of robotics and control. i'm looking for books or website with theoretical information and calculation. thank you eli

maybe i didn't explain myself... i'm an electronice engineer with specialization of robotics and control. i'm looking for books or website with theoretical information and calculation. thank you eli

Great answer, steve. Maybe you've sent a troll on his way.

Potential new RCM troll sez: "> maybe i didn't explain myself... i'm an electronice engineer with

Oh! OK, sorry! If you have qualifications as ""electronice engineer"" then you should already have access to the information you seek and you could tell us all about it.

Bob (on troll patrol this week) Swinney

"elitkh" wrote in news:1139737772.529327.23790 @o13g2000cwo.googlegroups.com:

Probably better to post this question over on sci.engr.control.

Those are excellent questions. They are also rather comprehensive questions of scope far broader than newsgroup responses can begin to deal with. You need to visit a library or a bookstore. If the latter, bring about $300 with you. You have some studying to do.

OK...OK

lets start again and focused the questions:

1) When should I prefer using AC motor and when brushless motors? 2) What are the benefits of each system?

i hope answers for those questions will give me somthing to start with. thank you for your geniality :) eli

What do you mean by "AC motor?" Most motors that you'll see referred to as AC servos are the same thing that other mfrs will call brushless motors. Most brushless motors are essentially permanent magnet synchronous 3 phase motors. Baldor uses the terms interchangeably...

Or by AC servo do you mean a system that uses an induction motor and, for example, a vector drive to control the motor?

Ned Simmons

AC-induction motor-controling by frequency inverter for example-is it possible to use such motor in position close loop? thank you eli

Yes, it is. If you go to the SEW web site above, you will find that they can supply the entire system including motor with attached position feedback encoder built into the housing ( it fits behind the fan) and frequency inverter. I've used them in the past with good results. One of their machines that they display at trade shows is a conveyor driven by this set up. It spends all day moving back and forth between two set positions.Accuracy is pretty good but I can't give you actual numbers on it.

Tom

Yes, this machine I built about a year ago uses an induction motor, a Yaskawa V/Hz (not vector) VFD, and a PLC to position the gantry. The commanded position and the encoder are the inputs to a PID function in the PLC, which in turn generates a pulse train that the VFD reads as a velocity command. The tradeoff is that the system is not as stiff and does not respond as quickly as a more conventional servo, but it does settle to within about .015" of commanded position from 20 inches/second with very little overshoot, with is more than adequate in this application.

Ned Simmons

Let me guess ... it's an automatic car wash for R/C model cars?

Pretty close. It degreases a small medical component. Two ultrasonic baths and four cascading rinse baths of DI water, all heated. The gripper that handles the parts baskets could easily be adapted to pick up model cars .

Ned Simmons

can you pls tell me why you decide to use induction motor and not permanent magnet brushless motor? thank you eli

Wow. Why did you go with an induction motor rather than, say, a stepper motor? I can see that your approach could give a lot of power and a pretty high slew rate though.

Jim

Money. The PLC, which was required to run the rest of the machine in any case, was capable of controlling the VFD/induction motor, but a separate motion controller would also have been needed for a servo amp/brushless motor system.

In this case the drive was small enough that the difference in cost between a servo amp/brushless motor and the VFD/induction motor probably wouldn't have been that great - perhaps $200-$300. In a larger system the induction motor would have a much greater economic advantage, if the reduced performance is acceptable.

I have noticed recently that some drives manufacturers are putting specs on the response time of even their lower end VFDs in the data sheets, which leads me to believe that more folks are using them in closed loop applications.

Also see my reply to Jim Rozen.

Ned Simmons

Before I actually tried it, I wasn't sure how well the control scheme would work. Using an induction motor, the fallback was to have the PLC control the VFD with three set speeds - slew, slow and creep - that would allow zeroing in on the desired position. I've done that before and it can work surprisingly well, but the programming is much messier than just plugging in a predefined PID function. The fallback wouldn't have been practical with a stepper.

A few other things drove the choice:

The load is constant and almost purely inertial.

The motor was available off the shelf inexpensively with a right angle hollow shaft reducer, which made the interface to the linear slide very easy and clean.

It's very quiet. The only perceptible noise is that of the linear bearings.

I don't usually like steppers, though save for the gear reducer, this would have been an OK app for a stepper. My usual objection to steppers is that servos are only marginally more expensive and offer better performance.

Ned Simmons

Thank you. We've been using a lot of stepper motors at work in precision control applications, where a servo setup would not work. But yours is a nice approach to controlling what could potentially be a lot of hp in a very precise way.

Jim