RE: [CAD_CAM_EDM_DRO] Big Servo Drives

That’s the way CNC Teknix tried to do it, sort of.

They have a PID control card that outputs digital PWM signals, and receives
current overload signals from the FET card.

The FET card has opto isolators to keep the PID board safe, and there are
two PID boards one for low voltage hi current motors, one for hi voltage
lower current motors.

It would have given the opportunity to make very much bigger hi voltage
cards, but first the dynamic range issue needs sorting to make the pwm card
suitable for bigger motors.



Really unless we are going to play with digital compensation / fudge factors
we need a PID control cards, and an analogue torque mode card, but these are
readily available on the market, but we didn’t like the prices. However over
the past year the prices have dropped considerably. I think those of us with
bigger motors are just going to have to accept the fact that we will have to
pay a bit more for our cards.

We could build a big servo card, but with the Rutex cards the FET’s were
coming in at £48 each time they blew, if we try to make something cheaper to
sell there has to be a profit margin and it just may not be viable.



Dr. Mark Vaughan Ph'D. B.Eng. M0VAU

Managing Director

Vaughan Industries Ltd, reg in UK no 2561068

Water Care Technology Ltd, reg in UK no 4129351

Addr Unit3, Sydney House, Blackwater, Truro, Cornwall, TR4 8HH, UK.
Phone/Fax 44 1872 561288

RSGB DRM111(Cornwall)

_____

From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of roboticscnc
Sent: 28 May 2007 07:40
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Big Servo Drives



Hi Group,
Forgive my ignorance as I'm not an electrical engineer, but after
reading the comments on this subject I'm wondering if it would be
helpful to have an external power board with overkill mosfets and
anything else necessary to remove back emf, etc. This way you could
use any servo driver to do the positioning function with the output
only switching larger mosfets - keeping high voltage / current noise
away from the encoder signals. The external power board could then be
designed for the correct power without dictating which servo driver
you have to buy.
Regards,
Glen.



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