Re: Why is the push to such high step rates (Grex and Arc100)?

256 microstep drive at 3,000 RPM equals a 2.56 MHz step pulse
frequency.

4,000 line encoder on a 6,000 RPM servo equals a 1.6 MHz step pulse
frequency.

Not all applications are low speed, low resolution.

Mariss





--- In CAD_CAM_EDM_DRO@yahoogroups.com, "lcdpublishing"
<lcdpublishing@...> wrote:

>
> I can't tell if this is turning into a peeing contest of specs or

if

> there is some actual merrit to these high rates. Assuming that

these

> are for machine tool motion control (yes I am well aware of other
> types of motion control) I am failing to see the point.
>
> With a possible frequency in the range of around 2 Mhz or more,

this

> works out to a pretty fantastic velocity. Assuming a resolution
> of .0001"
>
> 2000000 * .0001 = 200 Inches per second
> 200 * 60 seconds = 12,000 Inches per minute
>
> 12,000 IPM is about 3 times faster than the fastest commercial CNC
> machines on the market, and those use linear motors.
>
> We know that stepper motors have a very finite, useful RPM range.

The

> steppers I have been toying with recently have a limit of 500 RPM,
> beyond that torque drops very quickly. Assuming 200 steps per rev,
> the maximum useful frequency is
>
> 200 X 500 RPM = 100000 / 60 = 1666 Steps per second
>
> Even when factoring in microstepping of say 16 microsteps
>
> 1666 * 16 = 26,666 steps per second
>
> Servo motors certianly can run at much higher RPM ranges - many

around

> 4000 RPM. Putting that into some form of perspective relative to
> motion, assuming a .2" pitch screw and a minimum resolution

of .0001"

>
> 4000 RPM X .2" = 800 IPM (very fast for most industrial machine)
>
> 800 IPM / .0001" resolution = 8000000 steps per minute
> 8000000 / 60 seconds = 133,333 steps per second
>
> So with the potential of stepping rates into the millions....
>
> A stepper motor doesn't have enough torque at speed nor can it

handle

> that rate of stepping frequency.
>
> A servo motor, driving a relatively fine pitch ball screw at a
> resolution of .0001" doesn't need a stepping frequency in the

millions.

>
> Why is there such emphasis put on that level of performance in
> stepping rates?
>
> Chris (Confused as usual)
>