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Closed loop options?
« on: February 15, 2011, 03:48:35 AM »
Hello,
    I have a purchased a Milltronics Partner 4 Milling machine and it has been stripped of the electronics all except the spindle motor. I already had some Allen Bradley AC servo amps and .73Kw motors for the axis that accept Step/dir and also +/- 10v for control.
I want to be able to have closed loop control and I was wondering what are my options I have seen the Ajax and the dspMC/IP control boards and I like them but I want to look at all my options before I descide.
Also like I said the machine had no servos so do you think the 1hp servos have enough power for this mill?
I will look into all suggestions and thanks in advance for the info.

Offline Hood

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Re: Closed loop options?
« Reply #1 on: February 15, 2011, 07:04:03 AM »
If you have DDM or DSD drives then using Step/Dir will  give you closed loop between the motors and drives, so no need for Ajax or DSPMC.
One issue you may have is if using the parallel port then you will likely have to use electronic gearing in the drives as you will be unlikely to get the pulserate required from the parallel port. I use the SmoothStepper which allowed me to get my lathe from 3m/min with 2:1 electronic gearing to 15m/min with 1:1 electronic gearing.

Not sure the size of your mill but I tried H-3016 motors on my Beaver mill at 1:1 gearing between motors and screws and they were not enough, I ended up with 4030  and 4050 motors, but its a heavy mill so they might be fine for you at 1:1 connection if thats what you are doing.
I am however about to redo my Bridgeport as a test machine for different hardware and I am going to use the 3016 motors on it but I will be keeping the original 2.5:1 gearing that the Bridgeport had and it is fine in the initial tests I have done.

Hood
Re: Closed loop options?
« Reply #2 on: February 15, 2011, 05:36:23 PM »
Thanks hood for the info
   I knew that I would have closed loop between the drive to the motor but I will not have feed back into Mach like the Ajax would have and I though that would be better to have to guarantee the steps sent where steps received or am I not understanding the Ajax system completely?
I have some 2098-DSD-005 drives and MPL-A310P-MK motors that have .73kw(1hp) of power at 5000 RPM max.
The Partner 4 mill is close to size of a Bridgeport Series 2 that I had a few years back.
I will look into the smooth stepper but I want closed loop back to Mach in case of missed steps.

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Re: Closed loop options?
« Reply #3 on: February 15, 2011, 06:00:36 PM »
I dont think the Ajax will be true closed loop to Mach, it may have encoder feedback which if an error is more than a pre determined count then it will fault but not really closed loop.

I have the following error on my drives set to 20 counts   and if it ever goes outwith that it will fault my drives and signal to Mach to halt. That means if my motors are ever out of position by (5mm/8000)*20 = 0.0125mm  and I have never had that happen yet except when I was initially setting up the machines or I have crashed them.
The only advantage I would see from the Ajax system, if it is like I suspect, is you would not need to rehome after a fault as the DROs would get updated from the encoder.


On to your motors, I think you would need to gear 3:1 to have a chance of  using them with a mill the size of a Bridgeport series 2, my other mill, Beaver NC5 is about that size and the 3016 motors I tried were supposed to be 1Hp with continuous Torque of 2.2Nm and they were not good enough at 1:1 gearing. Your motors are only 1.58Nm cont torque.

Hood
Re: Closed loop options?
« Reply #4 on: February 15, 2011, 06:53:55 PM »
Hood
The 3:1 would allow what kind of speed with the smooth stepper would you say I would get with the Motors I have on hand?
I don't mind it being a little slower sense this is going to be used in my home shop and I could always upgrade the motors and amps later.
What do you think would be the best torque/power motor for the Mill size I have with 1:1 gearing?

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Re: Closed loop options?
« Reply #5 on: February 15, 2011, 07:00:17 PM »
I have just had a quick word with Brian as he was on his way out and he said Ajax and Galil are closed loop but not had a chance to querie him further as he was heading out.

Ok regards the motors, you will obviously get 5000rpm out of them so ballscrew would be going at 5000/3 = 1666 rpm so if you have the standard 0.2pitch screws that would be 333IPM you would get. Not sure what count your encoders are, think they are probably smart encoders but as the SS can pulse at up to 4MHz you should not have an issue there.
Hood

Offline Hood

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Re: Closed loop options?
« Reply #6 on: February 15, 2011, 08:01:47 PM »
Ok talked to Brian a bit more and from my understanding it seems how it works is Mach still plans the trajectory and passes that to the Galil (Ajax likely the same) and the Galil controlls the motors to keep them on track. The encoders are fed Back to Mach and the DROs are updated from that feedback but Mach does not actually update the trajectrory with that feedback.
So in other words it is the same as you would have with using the Step/Dir on the DSD's with the exception that there is no DRO update in Mach from the encoders. There will likely be encoder feedback at some point with the SmoothStepper but its not likely to be in this revision of it.

I can see a few benefits from the encoder feedback but in real terms it will not make your machine any more closed loop than it would be without them, well as far as the actual machining is concerned.
Where the feedback would be of benefit is if you had the drives disabled and the axis was moved then Mach would know, also if you E-Stopped then as long as your feedback was still active Mach would know the axis position, so it saves you homing but really that seems to be about it.

Of course this is just my understanding of my talk with Brian so it may be slightly different.
Hood
Re: Closed loop options?
« Reply #7 on: February 15, 2011, 09:53:08 PM »
You might want to look at EMC instead of Mach3 as your controller software.  It closes the loop in the PC, and there are pretty inexpensive interface boards available to connect directly to +/-10V drives.

Regards,
Ray L.
Regards,
Ray L.
Re: Closed loop options?
« Reply #8 on: February 16, 2011, 03:09:23 AM »
I do like the Smooth Stepper's output rate does it need an opto isolated breakout card between the Limit switches?
 My drive manual states the drives have opto isolation on the Step/Dir inputs so I should be good their. 
Also the motor data sheet states they have Multi-turn High Resolution Encoders but does not states pulses per revolution in the manual.
Would I loose position resolution if I setup say a 4:1 gear ratio on my Mill with the encoders of the motors that would be around 250IPM ?
Thanks for the help as usual

Offline Hood

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Re: Closed loop options?
« Reply #9 on: February 16, 2011, 03:47:50 AM »
I use a breakout board with my SS on my machines, more for the convenience of connection but also as a bit of added safety. I use the PMDX 122.
One thing I will recommend is that you convert the single ended step/dir outputs of Mach to differential, it makes them much more immune to noise issues.
Increasing the gearing mechanically will give you better resolution, think of it like this, if your encoder was 10,000 steps per rev and was direct coupled you would have 10,000 steps per screw revolution but if your gearing was 4:1 then it would be 40,000 per screw rev so a 4 fold increase in resolution.

Ok your encoders are sine/cosine and the default is 1024 counts per rev, you can  multiply this in the drive to get over 1 million counts per rev if you wish but no need for anything like that ;)
I have these kind of encoders on my lathe and mills spindles and I just have them set for 1024 but if it was an axis I would probably be looking at multiplying by 8. If I recall you can multiply by  2, 4 , 8,  16, 32, 64, ...... up to 1024

Hood