On Sun, 21 Mar 2010, Paul Keeton wrote:
> Date: Sun, 21 Mar 2010 11:39:57 -0400
> From: Paul Keeton <pkeet...@woh.rr.com>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <emc-users@lists.sourceforge.net>
> To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
> Subject: Re: [Emc-users] G52 and Fanuc conversion to EMC
>
> Peter,
>
> I have a question about the the 7i33. The machine we are discussing
> has three 25 HP spindle motors operating on 3 separate VFD's. We have a
> Italian control that was fitted onto a machine and it has a 100ma limit on
> its analog output. Each VFD requires a minimum of 70ma to run. We had to put
> a small phoenix contact amp on it to boost the analog signal to run all
> three drives on that machine. The problem comes when you turn one spindle
> off and only run on two. The RPM runs higher than it should due the
> decreased load on the circuit. In other words the analog VREF increases and
> the two drives have to be retuned. We get around this by putting a blank
> tool in the spindle and running all 3 wether they are cutting or not. Not
> only is this a waste of energy it also puts unnecessary wear on the unused
> spindles bearings. What is the limit of the analog out on the 7i33 channels?
> I can always use one out per spindle and that would completely solve the
> issue. What is your take on this? One output or three? Anyone else feel free
> to jump in!
>
> Paul
The 7I33 has limited output current capabilites so would need a buffer to
drive your VFDs. Since there is such high input current I would use one buffer
per VFD. Are these 0-10V + direction devices or +- 10V?
if 0-10V + dir, I may a have a solution coming (a single isolated output
spindle control with RS-422 PWM so it can be mounted near the VFD)
Peter Wallace
Mesa Electronics
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