Re: [CAD_CAM_EDM_DRO] EMC2 Servo Loop

Phil@Yahoo wrote:

> This is a question mainly for Jon Elson, being the EMC2 guru-
>
> You mentioned in a recent post that EMC2 can run the servo loop in the PC,
> which I presume means the PC is reading the encoder outputs. My question is:
> how can the PC read the encoder fast enough? I know there are some fairly
> significant delays in the parallel port speed, at least on output. Maybe
> that's not an issue on input? Also, where do you get enough inputs?
>

If you want to run the motors faster than the PC can handle with the
parallel port, then you need additional hardware.

EMC can use parallel ports (I think a maximum of 8 at a time) for PWM
(analog), step/dir, quadrature, and several other output types. It can
also read encoders, with or without index channels.

For faster machines, there are several companies that make hardware that
increases the maximum count rates. Jon's company is one of them (Pico
Systems). A basic servo interface kit can be had for around $200 to
$500, depending on how much additional I/O you want. For around $500,
you can get a PCI FPGA card plus interface daughtercards from Mesa
electronics which can generate control output (step/dir, up/down,
quadrature, PWM, PDM ...), count quadrature, and provide 72 I/O points
(some of which are taken up by the other functions if you enable them).
You can mix and match hardware as well - use a bare parallel port, a
Pico Systems parallel-connected card, a Mesa PCI card, and a Motenc
analog servo card all at once.

There are plenty of options, the hard part is deciding on which one to
use :)

- Steve