Re: [CAD_CAM_EDM_DRO] RE: PC based CNC system architecture

John Beidl wrote:

> I think the use of USB is a reasonable solution. It is true that
> transactions occur at 1 msec. rates, however, that does not mean it takes
> one more millisecond to get a reply from a device.

The problem is that for the servo control loops to be stable, they need
a very predictable sampling interval. If the USB 1 ms. message dispatch
clock cn be synchronized to something at the PC, that should be OK.
If the CNC program can synchronize to a stable and predictable
1 ms clock from the USB, that might also work OK. But, if that
1 ms is not predictable, and/or can't be synchronized or sync'd to,
then it is a big problem. Everything will be fine, and then suddenly
a message gets delayed by a whole extra mS, that would cause a
sudden jerk in the servo.

Jon