Hello Albert,

Depending on what size is your machine, you have to check the ballscrew size, fixation system and lead, thus take care about critical speed and related vibrations (go to Hiwin or something to see tables).
According to your requirements, I would go to servo system, but to handle good accuracy at high speeds (12-15 m/min) as you suggest. A system with BS and 5mm lead + a 3000 rpm motor probably can't run at full speed due to bandwidth problems (it might be different with high end and auto tuning systems).
So you have to accord the lead and accept a lower resolution, it's still better than running a a short lead ballscrew that you can't control. (High speed machines often use 10 to 20 mm leads and AC/DC brushless servos dedicated to this market. They usually run at 1500 - 2000 rpm nominal speed and may use high resolution feedback systems)
It's all about torque and bandwidth...
Dynamic speed control is mainly limited by inertias and resonance problems. It's quite complicated to explain that by few words but depending on your objective it could be much more difficult than bolt and plug&play.
Don't think that claimed nominal values are applicable values to a particular system.
I.e. I had to limit my maximal speed way below nominal speed to keep low following error, but my system can run faster... I chose the best option for me.

As Tom suggested me when I had to choose between step/dir and DAC speed control, go to DAC speed control, your system will be more responsive.

I personally Use Kflop+Kanalog and Industrial grade AC servo system.
This gave me very good results but some limitations due to ballscrew size which is limited by available space.

I hope this help,

Jerome

--- In DynoMotion@yahoogroups.com, "albertplatek" <albertplatek86@...> wrote:
>
> Hi Jerome,
>
> Speed around 200-300mm/s
> Motor drive following error not more than: 0.05mm (i mean digital error not mechanic) if less ofc better.
> Acceleration around 30 in/s2
> Type of cuts: mostly raster relief carving in wood
>
> Transmission: ballscrew + precision grade
>
> I want buy cnc router from china without control box, and no motors.
> Add Kflop + SnapAmp or 2xSnapAmp but I dont know what motors will be better:
>
> Drive Stepper as servo
> or DC brush servo motors?
>
> I heard that SnapAmp can control stepper motors like as servo,
> will it work something like EZI-Servo system?
> http://www.fastech.pl/index2.php?menu=2&page=show
>
> I already have china 6090 cnc router with ballscrew, precision grade,
> Stepper motors 86/86 - 4,6 Nm 5,5A, Geckodrives G203V and KFlop.
> It works great with acceleration up to 40in/s2
> Speed 140mm/s
>
> I do a lot of relifs on it but I need bigger router, so thats why I consider SnapAmp + servos.
>
> Yes I know that china routers are not top quality but with good contol system they do good job in wood.
>
> Best Regards
> Albert Platek
>
>
> --- In DynoMotion@yahoogroups.com, "Fouijar" <fouijar@> wrote:
> >
> > Hello Albert,
> >
> > This is the eternal question, I'm not the transmissions specialist but will answer following my experiences.
> >
> > The first question to answer is: "what are the technical specifications you expect?". I mean speed, precision (dynamic precision => following error),acceleration, type of cuts, rigidity of the overall machine and transmission...
> >
> > If you want everything it's possible but expensive.
> > Do you already have built the frame? What kind of transmission you intend to use: ballscrew (+ precision grade and backlash)*, rack and pinion ()*, belt drive (tensioning system, belt type, etc.)
> >
> > You can size your actual motor needs following your expected specs. with this software: http://www.kollmorgen.com/uploadedFiles/kollmorgencom/Service_and_Support/Technical/maesetup620.zip
> >
> > Now I still not answered your question, but I'll do simply maybe too much...
> >
> > Simple and low cost: stepper + rotary encoder
> > Normal: DC Brush servo
> > Better: AC Brushless servo (from 500$/axis to much more...)
> >
> > If you need this system for hobby purposes and have the time, stick to simple. If it's for commercial you'll need a well rugged system to avoid downtimes and mistakes. It does not mean AC brushless...
> >
> > I think it could be good if you answer the questions above to give you better advice.
> >
> > Regards,
> >
> > Jerome
> >
> >
> > --- In DynoMotion@yahoogroups.com, "albertplatek" <albertplatek86@> wrote:
> > >
> > > Hi Tom,
> > >
> > > I am going to buy Kflop and SnapAmp in future for woodworking CNC router
> > > It will be used mainly for wood carving.
> > >
> > > What will be better?: Drive a stepper as a servo motor or DC brush servo?
> > > What are the differences in performance, response, overshooting and vibration of motion?
> > >
> > > Best Regards
> > > Albert Platek
> > >
> >
>