Re: [CAD_CAM_EDM_DRO] Spindle RPM control

RichD wrote:

> CNC Idea!
> RPM control of a spindle motor (controller) with a frequency to voltage
> converter by using a spare axis CNC control program step output.
> The rate is set in any block with the F word as needed.
> The direction bit can control on/off/disable if wanted.
> The FVC output will substitute for the pot in a typical PWM full wave
> rectifier controller such as used in the Sherline machines.
> The KBE controllers can be used in this manner.
> This idea sort of is a poor mans constant velocity control or speed change
> for various reasons in special cases.
>
> Is this viable, plausible or practical?

The problem is that most CNC programs do coordinated motion on all axes
simultaneously, so the spindle would stop every time the other axes stopped,
and would be ramping up and down with every feedrate change as the axes
accelerated and slowed.

> I have not identified a VFC chip as yet. Do they exist?

Yes, but for this purpose, simple circuits might do just as good a job.
A pulse stretcher, made from a one-shot, followed by an integrating
op-amp to smooth out the pulses would do it.

Jon