Hi,
my new build mill has axis beds of 75kg. Thus I would expect the Y axis partiularly to be required to accelerate the X axis bed, linear rails,
ballscrew and servo, vice and workpiece AND control cutting forces. I anticipate the mass alone will be about 110kg. I am planning
direct coupling the servo to the 32mm diameter 5mm pitch screw.
I am of the opinion, and have calculations to support it, that it will work. The ratio of the moments of inertia between the servo armature and the ballscrew
and attached beds/mass suggest that I may have some fun trying to tune the combination. A medium inertia servo would be better in this regard.
Follow this calculation:
750W servo, rated continuous torque =2.4Nm
Effective radius of a 32mm ballscrew= 16mm =0.016m
[email protected]=2.4/0.016
=150N
Mechanical advantage of a 32mm diameter screw or 5mm pitch is:
mechanical advantage=32 x pi / 5
=20
Thrust ( at rated torque)= 20 x 150
=3kN
Lets say that half of that thrust is available to accelerate the axis and the remainder overcomes friction and controls cutting forces:
Accelerating thrust= 3kN x 0.5
=1.5kN
F=M x A or A=F /M
acceleration =1500/110
=13.6 m/s
2
The acceleration of my 110kg axis could be as high as 1.3g.....and thats only rated torque, if I allow axis tuning to use the the overlaod torque
I could accelerate at close to 4g!!!, and that still assumes ONLY ONE HALF of the torque is available for axis movement. More likely
3/4 to 7/8 in actual practice.
In short a 750W direct coupled servo is way more power than I can really use, 400W would still be more than adequate, but 750W servos
were only another $30 each so I got them.
I can have G1's of 15m/min (3000 rpm) and G0's of 25m/min (5000rpm).
Yes you can get your 3000rpm Delta servo to do 5000 rpm, using a feature called feild weakening. It loses some of it top end
torque, but hey I've got swags to spare!
I think you'll have more power and speed that you can possibly believe with the servos you have listed.
Craig