RE: [CAD_CAM_EDM_DRO] calculation of motor torque

Hi Boris

Ok... I will make a few comments for you.
One needs a good deal of overall design information
to do an exact motor sizing so I will be fairly general
at this point.

Accel in rapids can be fairly slow. It is much more critical
in cutting. I will just pick a typical value. Let's say you
want to stop or turn a corner in 1mm at cutting speed-perhaps
50 mm/sec. Accel will need to be about v^2/r or 2500/1=
2500mm/sec^2. Converting that will be 2.5m/sec or about
one quarter g. For different values you can figure your own numbers.

You certainly will need twin gantry screws to prevent racking.
You can use a single one with a moving table.

I have not calculated the EFFECTIVE inertia of the ballscrews, but
I can tell you it will be something like 150 kg!! So the flywheel
effect of those twin screws (even with the high lead) when converted
to linear inertia is 10 times that of the gantry- thus dominating the
dynamics.

For this I would strongly suggest using servos rather than steppers.
How big? 600 in oz or so peak for x. You can convert to nm. A somewhat
larger one would allow for direct drive. Extreme low rotor inertia
is not required for x. Matching the motor rotor inertia to the load
inertia is a good starting point but is not strictly required. That
and max speed defines the required screw pitch.

Les

Leslie M.Watts
L M Watts Furniture
Tiger Georgia USA
(706) 212-0242
http://www.lmwatts.com
Engineering page:
http://www.lmwatts.com/shop.html
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http://www.lmwatts.com/forsale.html
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http://www.lmwatts.com/signwp.html




-----Original Message-----
From: Boris Maraz [mailto:boris.maraz@...]
Sent: Monday, December 15, 2003 2:26 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] calculation of motor torque


Hi!

So I must tell a little more on my project. Basically this is cutting
router. It will cut some sort of polypropylene up to 1.5mm tick. So I guess
there is not much more force when you cut or not, either way 30cm/sec will
be G00. The router X axis is 1600mm and Y is 1200mm long. Z travel is 50mm.

The lead screw diameter will be KGS-1610 or KGS-2010 or KGS-2020 technical
information http://www.neffaa.de/eng/kgt.html. I think it will be necessary
to put two lead screws because of the wide of table 1200mm. Maybe also 2
steppers for X axis or just to connect it with timing belt.

The linear guides are ballbering. It runs very smooth.

So if I want 30cm/s the full move of X axis will last for 5.3333 seconds. If
the move will last 70% at full speed then acceleration and deceleration will
last for 1.6 seconds. So around 0.8 second for acceleration and same for
deceleration.

And about turn on corners is so that if the angle is change more than, lets
say, 50 degrees (for sure more than 90 degrees) it will stop and take out
cutting knife, turn it into new direction and put it down and start cutting
again. (tangential knife)

Thanks all for your time on my questions.

Boris




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