Re: Re: Old CNC controls

>
> From: Jon Elson <jmelson@...>
>
> "D.F.S." wrote:
>
> The threading does not use some fixed value for spindle speed, it
> measures
> spindle rotation with a spindle encoder, and each sampling interval it
> computes
> a new carriage position based on the spindle position.

Is this something EMC does "Out of the Box"?

I figured this would be the Best approach, but thought EMC could only
pre-calculate the positions of all the axis at any given instant, and
compensate to try and force everyting back into sync.
The only "Correction" is if things fall far enough out of sync, past
a defined parameter, was to simply stop with an error.

This is not the way EMC works?

Where is this compensation feature documented or is it a DIY kind of
function?

> There are 2 ways to go. The simplest is to get a variable speed drive,
> and hook
> it to the CNC controller for a speed command. This is open loop, but
> most
> of these units will keep the motor at very constant speed within the
> motor's and
> VSD's power ratings. (With a little more sophistication, the CNC could
> correct
> for load variations since it is reading the encoder already.)

I'll have to look into a control for my motor.
What is the usual speed variation that can be acheived had with one of
these controls?
I would presume there is only a limited frequency change that will
properly operate a motor designed for a fixed frequency.

> I built my own PWM servo amps, since I didn't know where to get them
> surplus at the time. It was a great education in control systems theory

I have a lot to learn, maybe it's time to pick my lessons.

I'll build one if necessary, or if the cost appears too high to me, but
I presume from that statement you NOW know of a source for surplus
servo amps?

Marc