Re: Does control s/w affect machine performance? max step rate

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<davemucha@j...> wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "ballendo" <ballendo@y...>
> wrote:
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
> > <davemucha@j...> wrote:
> > > I'm not sure if T-CNC or Mach are limited to a total of 45khz

of

> > all
> > > three(4?) axis combined on a move, or if each of 3(4?) can move
> > with
> > > each getting 45khz ?
> >
> > Dave, 45000 is the base step rate. At that rate(or a lesser

rate),

> > any or ALL axes can be stepped simultaneously.
>
> IIRC, Mariss posted a list of maximum stepper speeds based on frame
> size. It's not he end-all of charts, but I thought that only the
> NEMA23 exceeded 1,000 RPM with any practical energy left to move
> anything ?
>
> (couldn't find that post as yet)
>
> It that is the case, then the 45,000hz max step rate of the

software

> we have surpasses the max the motors can use.
>
> If that is the case, then the software we have available in almost
> all quarters has the ability to out-step the motors.
>
> Also, increasing stepper speed futher approches the area of
> dimminishing returns. To that end, I don't see the need to have
> faster pulse rates for steppers.

8X or 10X microstepping and higher speeds, like those used on CNC
routers can easily exceed the step rates available on the parallel
port.

.0001 resoulution with 8x microstepping, 100 inches per minute, and a
1/4-20 lead screw is:

.050= 20 pitch

100 ipm/.050 = 2000 RPM, /60 = 33.33 rev/second

.050 pitch/.00025 inch step resolution (1.8 degree stepper) = 200
steps per rev x 10 for micro stepping = 2000 steps per rev

100 ipm then is 2000 steps/rev * 33.33 rev/second =66,660 steps per
second

If you want to move this fast you have to drop back to 1/2 stepping
and settle for it's attendant cogging and resonance.

If you want a router moving at 200-300 inches per minute, multiply
this number by 2-3. 256,000 steps per second seems to be about the
limit for practical use. Most people don't want or need resolution
less than .00025, nor speeds greater than 500-600ipm, at least not at
the same time.

Remember that there are also step and direction controlled servo
systems available that handle much higher encoder counts per second
(up to 256,000 in the case of DeskCNC servo drivers). Unless the
step rates can match, the PC controller software will become the
bottleneck and will limit the max speed.

Fred Smith - IMService
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