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Author Topic: Setting new cnc router build to achieve max servo speed  (Read 1277 times)

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Re: Setting new cnc router build to achieve max servo speed
« Reply #10 on: April 14, 2018, 02:48:28 PM »
Hi ger21,
Quote
A 500 count encoder is usually 2000 pulses/rev with quadrature. Which gives you 400 steps/rev.
I don't understand. A 2000 count per rev encoder requires 2000 pulses to rotate one turn?????

Craig
My wife left with my best friend...
     and I miss him!
Re: Setting new cnc router build to achieve max servo speed
« Reply #11 on: April 15, 2018, 02:08:37 AM »
I'm using DG4S-160 35 servo drives and can vary the voltage between 65 and 90V DC. The encoders are fitted on the motors and so that gets me close to 100Khz, then I have to set Mach3 to that frequency and try these settings our as soon as I get the pulleys in place and see what happens.
Thanks guys for the support, I'll post the results later on next week.
Marting
Re: Setting new cnc router build to achieve max servo speed
« Reply #12 on: April 15, 2018, 02:20:50 AM »
Hi,

Quote
then I have to set Mach3 to that frequency

NO, this is incorrect. Your UC300 will have to be set to and capable of 100kHz but Mach does not. Mach3 is a Gcode interpreter and trajectory planner, it at no time produces pulses. Pulses are produced by
a MOTION CONTROLLER, in your case a UC300. In the old days everyone used 'Mach Parallel Port Driver' as a motion controller, but the Parallel Port Driver IS NOT MACH3. It happens to use the same
CPU in the same PC that the Windows application 'Mach3' runs but they are separate.

Setting the kernel speed in Mach when you have an external controller like a UC300 is redundant, having said that apparently the CNCDrive plugin runs best when Mach3 'runs' at 25kHz, despite the fact you will
have to set your UC300 to run at 100kHz.

Craig
My wife left with my best friend...
     and I miss him!
Re: Setting new cnc router build to achieve max servo speed
« Reply #13 on: April 15, 2018, 04:45:25 AM »
Ho, I see! Definately didn't know that and coming to think of it this makes sense. I'll have a look at UC300 literature then and see what i find. Thanks for the eye opener Craig! Dunno what novices like me do without guys like you on the forum!
Thanks
Marting
Re: Setting new cnc router build to achieve max servo speed
« Reply #14 on: April 15, 2018, 04:52:43 AM »
Hi,
the UC300 has a kernel speed, it can be 25kHz, 50 kHz or 100kHz. You set it in the UC300/Mach3 plugin.

An Ehternet SmoothStepper from Warp9 can go at 4Mhz, 40 times faster than a UC300 can!

Craig
My wife left with my best friend...
     and I miss him!
Re: Setting new cnc router build to achieve max servo speed
« Reply #15 on: April 15, 2018, 05:02:09 AM »
Yep, just had a look at the literature and understand what needs to be done, also I'll have alook at the Ehternet SmoothStepper from Warp9 you mentioned as an alternative in case I'm not happy with the results.
Marting
Re: Setting new cnc router build to achieve max servo speed
« Reply #16 on: April 15, 2018, 05:26:18 AM »
Hi,
the UC300 will be fine. The truth is that beyond 100kHz you need to be pretty damn good with your signaling electronics and cables otherwise the signals just don't arrive at the
servo drives.

I have an 1.8kW Allen Bradley AC servo and drive I bought second hand I bought to make a high torque low speed spindle for my mini-mill. I can signal it at 200kHz single ended, ie just a normal
hook-up, or up to 500kHz with differential signaling using the sort of electronics that computers signal each other. To run it at maximum speed , 3500rpm at maximum resolution, 8000 count per rev, requires a
pulse rate of 466kHz. Its doable but I use electronic gearing to knock that back to 93 kHz (divide by 5) and make the signaling situation that much easier.

The only real advantage of the ESS being able to go at 4MHz is if you wish to read a high resolution encoder at high speed.

I might point out that this Allen Bradley servo is the first AC servo I've ever had a chance to experiment with and they make DC servos look like absolute s*********t. They are just so much more controllable
and flexible, I'm not going to bore you with the details but when you get your hands on one you will ask yourself 'why didn't I get into these years ago?'.

Craig
My wife left with my best friend...
     and I miss him!
Re: Setting new cnc router build to achieve max servo speed
« Reply #17 on: April 15, 2018, 06:43:54 AM »
I know exactly what you mean but for now I've got plans for this cnc and need it to be up and running in the shortest time possible, so I suppose I have to do with what I have for now at least until it has generated enought to think about getting it Ac servos.
Thanks
Marting
Re: Setting new cnc router build to achieve max servo speed
« Reply #18 on: April 15, 2018, 07:35:34 AM »
Hi,
yes the flexibility of AC servos is amazing. They all have 'torque mode' for instance. Not really applicable to CNC but it means that you produce an analogue voltage (or PWM)
and the servo produces a matching torque irrespective of speed. You can imagine that would be just the thing in a printing press where you want a certain tension in the roll of paper no matter how
fast it is passing the roller.

Another useful feature in my Allen Bradley servo and I think its commonplace among AC servos is dual mode. It means for instance the primary control mode might be position control
via step direction pulses but changing on input to the driver and it will revert to secondary control which might be analogue voltage controlled speed mode. In fact this is what I'm working
on for my servo spindle in my mill. Mostly analogue voltage controlled speed mode is adequate but if I want to do rigid tapping I need position control. With this feature change one digital
input and I can have either.

All in all very impressive and I'm still finding out new wrinkles.

Craig
My wife left with my best friend...
     and I miss him!
Re: Setting new cnc router build to achieve max servo speed
« Reply #19 on: April 15, 2018, 07:47:51 AM »