Re: Bridgeport motor question

Another way for the software to directly control the spindle RPM is
to use the serial interface to the VFD and command the required
frequency directly. This also has the advantage of returning the
percent load on the spindle for display on the control.
Jeff

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> Tim Leech wrote:
>
> >How do you control the speed? I'm hoping to do it eventually via
the
> >software, & will be grateful for any pointers on that.
> >
> >
> Most of the newer VFDs have provision for a manual pot or a 0-10 V
> external signal to control speed. Check the specs, however, as the
analog
> input is an extra-cost option on some models.
>
> Once you have a VFD that accepts an analog voltage, then you need
software
> in the CNC program to handle Snnnn commands in the G-code and
> convert that to an analog voltage. Mach1 and Mach2 apparently do
this
> with software-generated PWM waveforms which you just average with
> a resistor and capacitor. You'd need an op amp circuit to raise
the maximum
> voltage level to 10 V. Using EMC with the Servo-to-Go card or my
> PPMC board set you can get a 0-10 V output from an unused DAC
channel
> to control spindle speed.
>
> Jon