Re: [CAD_CAM_EDM_DRO] Servo Motor Selection

Jason Cox wrote:

>John Elson and All on the list,
>
>I solved the cogging problem with my Ametek servo, like you said it was a funny brush and the more I run it the better it gets. The other problem as you said was actually a dud encoder connection.
>
>

Great!

>I am in the process of selecting servo's for a full size machining center. I want to run the machine with 700ipm max rapids and 600ipm Max Feedrate. The wieght of the x axis table is 200kg (441lb) and the wieght on the yaxis with the saddle is 300kg (661lb)
>
>The xaxis travel is 500mm and on the y is 400mm, I am using 1" dia ballscrew with a .250 lead. I am designing for a cutting force of 2000lbs (8896N) max.
>
>My calculations say that for my ballscrew to reach 2000lbs thrust I require 9.06nm at the screw or 80lbin.
>
>That I need around 2900rpm at the screw.
>
>That the x axis given 2000lbs of thrust constant will accel at 45ms^2
>
>And will accel to 700ipm in .0067 seconds. I dont think this is right.
>
>By my calcs I require motor 2?
>
>

Why? Motor 1 will provide 23.3 Nm (peak), and you say you only need 9.
23 Nm
should provide your full acceleration PLUS cutting load simultaneously,
with direct drive! The Continuous stall torque is almost that high.
So, you
could deliver 7.8/9.06 * 2000 = 1721 Lbs continuously at stall, or 1640
Lbs continuously at 2000 RPM. Do you really expect to deliver cutting
loads exceeding 1600 Lbs continuously? Can your spindle motor take
this without burning up?

If still in doubt, try it with a 2:1 reduction ratio. Then, the motor
should
be able to deliver at least 10 Nm to the screw at full speed, continuously,
extrapolating the chart a bit. That will only demand 5 Nm from the motor,
at 5800 RPM.

>The motors I have to choose from are as follow, in order of price:
>
>These are all AC brushless servo's.
>
>Motor 1
>Cont. Stall Nm : 7.8 (69lbin)
>Peak Nm: 23.3 (206.2lbin)
>Rated Torque at 2000rpm: 7.46Nm (65.5Lbin)
>Rated Torque at 4000rpm: 6.8Nm (60.2lbin)
>Max revs: 6000rpm
>Vrms/Krpm: 45.9
>Nm/A:0.76
>
>Motor 2
>Cont. Stall Nm : 12 (106.2lbin)
>Peak Nm: 56 (495.6lbin)
>Rated Torque at 2000rpm: 11.42 (101lbin)
>Rated Torque at 4000rpm: 11(97.4lbin)
>Max revs: 3000rpm
>Vrms/Krpm: 45.6
>Nm/A:0.75
>
>

Jon