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Hi All,
Currently I run a 24vdc 6amp linear power supply to my steppers. I also have my frequency set at 35K. My Ballscrews are 5TPI and step set at 1/16th micro step. I can only do 3amps max to the stepper as this is the limit of my steppers per phase and I have that set on my drivers. Currently my max Rapids are 200IPM. I would like to increase this. I can get more but go into mid band resonance problems over 200IPM. I do have Dampners for each stepper on the rear shaft. Rattler type, as well as rubber isolation from the frame on all steppers ( this has eliminated 99% of all resonance problems below 200IPM.

By changing to say a 40VDC power supply I know I will increase speed that's a given.
My question for you is this. Do you think I will still experience the mid band resonance over 200 IPM? maybe changing my freq to 25K with the added Voltage may increase the speed and minimize the resonance? I cannot go to 45K freq with my steppers as that is the next Freq in Mach3 and my steppers and drivers will only handle up to 40k freq
BTW these are nema23 frame type.
Maybe changing the step pulse from 5us to lower? what do ya'll think?

Anyone with food for thought on this, I would appreciate our input.

Mike

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I'm outside looking in, just farther from the window than most.

Well I guess no one has any thoughts on this?
mk

_________________
I'm outside looking in, just farther from the window than most.

Mike,
When I built my router I used servo's but I am thinking back to some of the issues I had to figure out when I considered steppers. If my math is correct (please check me on this). You are going (200 ipm x 5 TPI x 200 steps/rev)/16 micro steps = 12,500 pps. This is good and within the limits of Mach 3. What is concerning is you are running your Stepper at 1000 RPM which sounds high since they are best run at lower speed for peak torque. I believe steppers are best run less than 100 rpm range for peak torque (depending on the torque curve of the motor). Do you know if your motors have enough torque to move your machine at the higher rapids given the torque drop at the higher RPM's?

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Brad
Avon, OH

First I rechecked my setting and I forgot I had reset my resolution to 1/8 microstep not 1/16th. This puts me in the 8000pps range where the torque drops from 3nm at 200rpm 500PPS, down to about 1.2nm at 1000rpm at around 8000pps. I should be able to get 350 to 400 IPM with the 40vdc supply and my torque would still be exceptable for the mass I have to move. I could change from unipolar to bipolar parallel wiring and gain some torque but I don't see that advantage at this point. I'm more concerned about the Resonance issue. I just hate to waste the money when I'm thinking that the resonance issues won't change. I can get 300IPM now but again I get resonance issues at anything over 200IPM usually from direction changes only. These most likely are caused by mass/acceleration at that High of feedrate/rapid. Nema 23s are notorious for these problems. I can dial out some of it by lowering the acceleration but that defeats the purpose. I need the small rapid moves to be at max in order to see any gain. I really don't want to redo the entire machine to go to nema 35s. I would be better off selling this one and building a new one from scratch using servos.

Don't get me wrong 200 IPM rapids are fine but faster rapids would speed things up for me. My milliing feedrates would most likely not change anyway as I have found the optimum Feeds and speeds for most that I do. But I do cut a lot of small parts and there are many rapid moves made when milling multiple hundreds of the same part out of a single sheet. By speeding that up to say 300 IPM, would increase my productivity by 15%, in an 8 hour day that's a 72 minutes saved in that 8 hour time frame. 72 minutes is approx 80 more parts a day. At $0.75 each that adds up to dollars.

Brad, Thanks for the food for thought on this and you may have solved my issue as it does look to be more of a mass/torque problem. I just needed someone on the outside to look in from the other window to see it.

any suggestions or pitfalls are welcome for discussion please.

MK

_________________
I'm outside looking in, just farther from the window than most.

I am not real aware of Nema23's and resonance issues but it sounds like you have done your homework. If it is mass/torque related you could try setting your machine right to the edge where you are getting problem and then remove your router motor from the router (a fairly large mass) and run the tests again to see if the problem goes away? This may just be an indicator of the affects of mass on your specific setup.

You could also try your question at CNCzone.com since they have a fairly deep base of users that have built and probably had similar challenges.

Did you build this router from scratch? Do you have any pics?

Good luck.

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Brad
Avon, OH

Yes Brad I built it from scratch. I'll get some pics up. CNC zone is such a mess to ask questions in. I gave up on the Zone a long time back. I think your idea of removing the router may be a valid test. I'll give a it a go and see. I need to do some work on the rig anyway.
Thanks
MK

_________________
I'm outside looking in, just farther from the window than most.