RE: [CAD_CAM_EDM_DRO] CNC Controler Software

At 15:06 23/08/2004, you wrote:

>I realize that a RTOS or dedicated signal generator can produce stable
>pulse rates, but what I don't grasp is what is the result. That is to
>say, if I first machine a part using a CNC controller running under
>windows with no signal generator, and then secondly machine that same part
>using a CNC controller running under a RTOS or using a real-time signal
>generator, what will be the difference in the two parts?
>
>My initial thinking would be that the first part would be getting the
>exact same signals as the second part, just not with a consistant time
>interval between each signal. I understand complexity of the part
>dictates plenty, but I'd like to have my machine capable of a range of
>complexity.

Archie -

The difference will manifest itself in the speeds that the machine can
attain, and in the likelyhood (or otherwise) of the machine losing steps
when operated near to its max speed. In bad cases, you would see loss of
position (i.e., the part would not be the shape you want it to be), and
potentially poor surface finish as well.

You need a consistent pulse rate (i.e., a consistent time interval between
pulses) in order to achieve the best performance out of stepper motors. If
the pulse train exhibits a large amount of "jitter" (differing time
intervals between pulses) relative to the average time interval, then the
probability of mis-stepping will be large (and will indeed increase with
the motor speed). When the pulse rate is high enough that the "jitter"
component is likely to be comparable to the average time between pulses,
then the performance will suck bigtime (at least, I think that is the
technical term...)


Regards,
Tony