Hello Guest it is January 18, 2020, 06:26:32 PM

Author Topic: AC Servo's and Mach 3!  (Read 16217 times)

0 Members and 1 Guest are viewing this topic.

AC Servo's and Mach 3!
« on: January 12, 2011, 04:11:33 PM »
Alright, I've got an old hot wire cutting machine that is 2-axis movement with a 3rd axis turntable that's currently not in use, used for shaping styrofoam through the use of high resistance wire.  The computer that was controlling this machine had an ISA control board from Delta Tau Universal PMAC Dashlite that was running through a program called Vectorworks. The motors on the machine are Baldor brushless servos with resolvers and the drives are Baldor FlexDrives. Now, before anyone jumps on the fact that the motors have resolvers, the Baldor Flexdrives convert the resolver input into a digital ppr encoder output for the signal back to the computer.

I've done a great deal of reading and searching as well as pinning out this box so that I know what's hooked to what and I've definitely raised a few questions.The Flexdrives have a Pulse and Direction input on a Master Encoder in (http://www.baldor.com/support/literature_load.asp?ManNumber=MN1902 , page 66 of the PDF or 4-14), however it appears to use RS-422 as a communication protocol which involves +/- 5v instead of 0-5v. The digital inputs on the drive are all 24v controlled and currently the machine is hooked up to run an analog signal out to the drive for control, so it would have to be changed to pulse and direction. The digital inputs would have to be wired into isolation relays to talk back to Mach3 in a safe manner as well I assume.

So, my first question is flat out can Mach 3 work with these drives? The follow up question to that is what drives (servo or stepper) *does* Mach 3 work with as I cannot find drives that seem to play nice with 0-5v signals at all. It would be incredibly nice if there was a solid list of compatible drives so that if people were looking to retrofit then more of the information was readily available. If anyone can provide any help or direction I would appreciate it a great deal.

Ryan Schaffer
Fin Pan, Inc.

Offline Hood

*
  •  25,856 25,856
  • Carnoustie, Scotland
    • View Profile
Re: AC Servo's and Mach 3!
« Reply #1 on: January 12, 2011, 04:21:06 PM »
Mach sends out Step pulses and Dir signals and any drive that can accept 5v Step/Dir signals can be used.
Mach does not take encoder feedback as the loop is closed in the drives.
I have not looked at the pdf yet but if your drives can accept 5v step/dir signals then they will be fine.

Hood
Re: AC Servo's and Mach 3!
« Reply #2 on: January 12, 2011, 04:28:17 PM »
Well, I think that's the problem is that they want the RS-422 differential line driver, which is +/- 5v not 0-5v and in the mach 3 manual it says that's a definite bad idea. But I'll let you look it over if you'd be so kind. CNC control hardware is relatively new to me so I may also be making a mistake in my assumptions as well.

Offline Hood

*
  •  25,856 25,856
  • Carnoustie, Scotland
    • View Profile
Re: AC Servo's and Mach 3!
« Reply #3 on: January 12, 2011, 04:31:25 PM »
Ok just had a quick look and it seems like you should be fine. The signals it is talking about is differential Step/Dir signals and Mach only puts oiut single ended step/dir signals.
This however is not a problem as it is easy enough to make up a small circuit to change the single ended outputs into differential outputs, all that is needed is a line driver. You can also buy line drivers from the likes of US Digital.

I use Allen Bradley DSD drives and have made up a line driver circuit for myself, see attached pic,

Hood
Re: AC Servo's and Mach 3!
« Reply #4 on: January 12, 2011, 04:37:40 PM »
Excellent! Now if we were looking to replace the drives, is there something more easily plug and play with Mach 3? I have 2 other machines I'm looking at retrofitting as well and need to have an idea of the types of drives I can get for them that will  make integration a little easier.

Offline Hood

*
  •  25,856 25,856
  • Carnoustie, Scotland
    • View Profile
Re: AC Servo's and Mach 3!
« Reply #5 on: January 12, 2011, 04:47:17 PM »
I would stick with the AC Servos, integration is fairly straightforward, I use a PLC (via Modbus) to send/receive the 24v signals from the drives and using 24v is much superior to using 5v. Other 24v signals from things such as limits/home switches are best sent direct to Mach and can be converted to 5v with a simple relay or elictronically but afraid I am no electronics whiz so just use the relays. A lot of breakout boards are now starting to utelise 24v inputs so might be looking at that route, I think PMDX do one.

As for other drives, there are plenty industrial drives but the price is also industrial ;) Automation Direct do the Sure Servo range which are a bit cheaper and also there are the Chinese drives/motors that are coming on the market which are reasonable in price.
One thing however is it is not as easy to mix and match AC motors and drives as it is with DC motors so best to stick to matched sets.
Hood
Re: AC Servo's and Mach 3!
« Reply #6 on: January 12, 2011, 11:38:12 PM »
Yeah I'm no electronics whiz myself and most of my experience is with industrial control software and hardware, which believe it or not I find a lot easier to integrate than I do PC based solutions. So you're using 24vdc relays to transfer the limit switches back to the computer, and modbus out to the plc for communicating pulse and direction? Industrial price doesn't bother me because I'm in an industrial situation and a lot of the DIY stuff isn't a robust enough solution for the environment I'm in. I'm incredibly familiar with Automation Direct as we have been going through a progressive process of eliminating AB PLCs and replacing them with various series from AD. And I'm also familiar with AC servo drives for more classic industrial solutions, so matched sets are my friend anyways.

Do you happen to have any good resources for breakout boards that you like and make integrating relatively easy? And other than that do you have drives and motors that you particularly like?
Re: AC Servo's and Mach 3!
« Reply #7 on: January 13, 2011, 12:31:02 AM »
Oh and as a side note, you use the PLC to communicate to the 24vdc to the drive, but your pulse and direction runs through your line driver into the master encoder input?

Offline Hood

*
  •  25,856 25,856
  • Carnoustie, Scotland
    • View Profile
Re: AC Servo's and Mach 3!
« Reply #8 on: January 13, 2011, 10:16:12 AM »
So you're using 24vdc relays to transfer the limit switches back to the computer

Yes, I have 24v coils and have 5v on the contacts.


and modbus out to the plc for communicating pulse and direction?

No, the Step/Dir are from either the parallel port if you use one or I use a SmoothStepper as it allows me to have a higher pulserate which means I dont have to use electronic gearing in my servo drive.

I'm incredibly familiar with Automation Direct as we have been going through a progressive process of eliminating AB PLCs and replacing them with various series from AD. And I'm also familiar with AC servo drives for more classic industrial solutions, so matched sets are my friend anyways.

I use the D0-06DR PLC from Automation Direct on my lathe and mill. I use it for signals such as enables and reset to drives and also signals from drives such as fault etc I also use it for FRO and SRO pots and all the switches I have on my panels.

Do you happen to have any good resources for breakout boards that you like and make integrating relatively easy?

I use the PMDX 122 but if doing another I think I would look at the PMDX 126 as its a dual port board and the SmoothStepper fits onto it and also I think it can handle 24v inputs, so 24v limits could go direct instead of through relays.

And other than that do you have drives and motors that you particularly like?

I have only ever used Allen Bradley DSD or Giddings and Lewis DSA drives, they are identical just a different name. As for motors I use Allen Bradley/G&L H series, F series, N series and MPL series. I have bought them all seconhand the most I have paid was £180 for a 22KW drive and £250 for a 12.5KW motor



Oh and as a side note, you use the PLC to communicate to the 24vdc to the drive, but your pulse and direction runs through your line driver into the master encoder input?
Step/Dir goes from computer to SmoothStepper (Via USB) to PMDX 122 breakout then line drivers then drive.

Hood
« Last Edit: January 13, 2011, 10:18:06 AM by Hood »
Re: AC Servo's and Mach 3!
« Reply #9 on: January 13, 2011, 10:44:20 AM »
Thank you Hood! I appreciate it a great deal. I spent a little bit of time on the phone with the PMDX guys as well and they're helping me out with some of the finer points. If this works well and reliably I will definitely be looking at retrofitting all 3 of my current systems so that I've got a standard interface for my operators.