Re: Low cost Servo Controller

Well, the difference seems to be that Jons amps and
the Analog amps from AMC are indeed PWM amps,
but not PWM controlled amps.

Steve

----------
From: Bertho Boman <boman@...>
To: CAD_CAM_EDM_DRO@onelist.com
Subject: Re: [CAD_CAM_EDM_DRO] Low cost Servo Controller
Date: Tuesday, September 14, 1999 11:36 PM

From: Bertho Boman <boman@...>

I do not know anything about the AMC amps but is there a chance that the
controller actually sends a velocity command as a
digital signal. One byte would give sign + 128 speed levels.

Actually, it makes sense to communicate digitally to the servo amp and then
put the D-A internally in the servo amp. Less noise
and less headaches in general. I have been thinking of using the parallel
port to send a byte per channel for the servo amp. I
have not checked if 128 levels are enough but I think it is.

Although, sticking to the +/- 10 VDC standard is very desirable as I
mentioned earlier.

One advantage with the digital link is that the servo amp can be either
analog all the way or with PWM or it can be DSP based
and all digital and read the tach for velocity feedback. The encoders
wires can continue and be connected to the PC as usual,
the DSP would just monitor the encoders too.

Bertho
==========================

> From: Jon Elson <jmelson@...>
>
> The STG card expects the servo amp to accept analog input.
> These AMC amps apparently expect the PWM waveform to
> be generated by the CNC control. They are totally incompatible
> with EMC anyway, as the PWM waveform controls motor current,
> but the EMC is sending a velocity command to the servo amp.
> So, the servo amp must take velocity in, compare to the tach
> signal, and compute internally what motor current is desired.
> (This is an easy computation, at least at the first order, well
> within the capability of an op-amp.)
> --------> snip
> Jon

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