Re: [CAD_CAM_EDM_DRO] LARGE Gantry table

cutthroatplasmaco wrote:

>
> Can someone point me in the direction of suppliers for motors/drives
> for LARGE gantry machines... I'm talking 20'x40' cutting area. Off
> the top of my head, I'm guessing the gantry might way a half ton or
> more. I'm very familiar with smaller steppers/servos, I just don't
> quite understand where/what route you take when talking about large
> machines that need significant torque to make a 1000lb gantry change
> directions on a dime.

Chris:

Here is our experience (with a big 10,000 lb Jones & Lamson TNC 312 cnc lathe):
The stock servo motors (not to be confused with the 240VDC 100 Amp spindle motor!)
were 60 volt 90 amp max motors driving 2" dia 5 TPI ballscrews.

Using one of my 1500KW supplies (in a 60VDC output, single 47,000uF cap version),
we used Gecko G340's (I'd use the cheaper G320's next time). The carriage we
estimated at approx 1500+ pounds, and was set up for 2 inch/second max speed
(using DOS-based TurboCNC on a Pentium 350 emitting 40,000 steps/second).

The motor-mounted encoder was 1000 CPR (4000 counts in quadrature/revolution),
and thus each 'Z' step was 50 millionths. We could accelerate the whole mass
to top speed in 0.250 second. We could issue single steps and see the 50 millionths
(ie half a tenth) on the tenth reading dial indicator. Not only that, but we could
slam the carriage to a high speed (normal non-ESTOP) stop, and the 1500 lb carriage
stopped within a tenth (of a thou). Pretty impressive. BTW, the X (cross axis)
motor had a 2000 CPR encoder giving 25 millionths (of an inch) steps!

Summary: Even though the geckos could only emit 20 amps (compared to the motors
maximal rating of 90 amps), we could do a fine job of precisely moving the 1500 pound
carriage.

However, for a gantry router, because your desired speeds are probably double or
quadruple our 2 ips, your mechanical leverage will be less, and hence your accelerations
will be less (but perhaps still in the 'acceptable' range).

cheers
Doug Fortune
http://www.cncKITS.com