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Acceleration calculations
« on: May 30, 2006, 12:18:19 PM »
Hello,
I dont know if it is pertinent to ask this on this forum, but here we go.
I am building an OEM machine which has a shuttle that weights 220lb. I want to size the servo to be used to move that shuttle as fast as possible and with as much acceleration as possible. This is to reduce cycle time as much as possible. The shuttle would make moves like the one at the end of the post (in INCREMENTAL MODE).

I am trying to come up with the max acceleration that a servo would be able to get me.
If I use a 3Kw ac servo, which has a constant torque of about 14Nm going trough a 4:1 reduction and a 2"sprocket (chain drive) gives about 2240N of force on that shuttle. Now If I want to find out the max acceleration I could get I would use F=ma, so 2240N=100Kg*a[m/s2] which solving for "a" gives a=22.4[m/s2] which converting to in/sec2 gives out 881 in/s2. Is that what I should use when tuning my servo? and should I expect that to be the acceleration i should get?

Hope I made sense.
thanks
Fernando

(shuttle movement test in incremental and inches)
G61
G91
F1500
G01 X10
G01 X1
G4 P.1
G01 X1
G4 P.1
G01 X3
G4 P.1
G01 X1
G4 P.1
G01 X1
G4 P.1
G01 X3
G4 P.1
G01 X1
G4 P.1
G01 X1
G4 P.1
G01 X3
G4 P.1
G01 X1
G4 P.1
G01 X1
G4 P.1
G01 X3
G4 P.1
G01 X1
G4 P.1
G01 X1
G4 P.1
G01 X3
G4 P.1
G01 X1
G4 P.1
G01 X1
G4 P.1
G01 X3
G4 P.1
G01 X1
G4 P.1
G01 X1
G4 P.1
G01 X3
G4 P.1
G01 X1
G4 P.1
G01 X1
G4 P.1
G01 X3
G4 P.1
G00 X-50
Re: Acceleration calculations
« Reply #1 on: May 30, 2006, 02:10:15 PM »
I would look to run it at a bit less than that :) Tune it in at about 500in/Sec^2 and I think you will be very happy...


Hope that helps
Brian
Fixing problems one post at a time ;)

www.newfangledsolutions.com
www.machsupport.com
Re: Acceleration calculations
« Reply #2 on: May 30, 2006, 03:18:07 PM »
ok, why set it to 500? when the continuous torque can get to 800? the max torque is far more than the 14Nm.
Are the calculations I made correct?
what acceleration do you have on the automation direct 1kw servos you have?
Another question off topic about your servos, is it possible to lower the encoder count on the driver electronically? If resolution is not an issue in this application, instead of having a 2500 ppr encoder that wouuld translate to 10,000 steps per recvolution, can the driver be programed to lower that count?
Regards and thanks for your comment
Fernando
Re: Acceleration calculations
« Reply #3 on: May 30, 2006, 08:22:52 PM »
There is a gearing setting that you can tell it for every step that you take in Move 10 pulses... That is going to be noproblem!

If you are going to do the 800in/sec^2 take great care in picking out the parts that it is going to be moving... you are going to be impact loading the chain and it is not going to take long to kill the chian...

This is going to be a cool machine  ;D
Fixing problems one post at a time ;)

www.newfangledsolutions.com
www.machsupport.com
Re: Acceleration calculations
« Reply #4 on: May 30, 2006, 08:28:46 PM »
correction... scary machine.
I kind of need the most acceleration possible, on the small moves it is going to make speed doesnt make much of a difference as acceleration would.
If the machine just tries to run off with the moves, or destroy itself, i will just have to lower the acceleration. But the goal is to lower the cylcle time as much as possible. trying to keep that gcode i posted under 20 seconds. If I can make it 15 or 10 seconds... WOWW!!!
Tell you how it comes out
Fernando
Re: Acceleration calculations
« Reply #5 on: June 02, 2006, 11:20:54 AM »
I am thinking that the slack of the chain (its a long chain, about 4m between sprocket centers) will make the shuttle move even when the servo is stopped, specially with those accelerations and impacts, any suggestions?
I was thinking maybe to use two servos, one on each side of the chain drive as to keep the top side of the chain as taut as possible.
Ill try it out anyways.
Regards
Fernando
Re: Acceleration calculations
« Reply #6 on: June 02, 2006, 11:35:34 AM »
Put a spring on the chain that is pulling at two times the force that is needed to accel that load and you should be okay (The spring could be an air cylinder ;) )
Fixing problems one post at a time ;)

www.newfangledsolutions.com
www.machsupport.com
Re: Acceleration calculations
« Reply #7 on: June 02, 2006, 11:52:34 AM »
Thanks Brian,
I had thought of putting a torsional, (rotational??) spring on the shaft of the not driven sprocket. Let see how it all goes.
In your expert opinion what would be better in terms of wear and tear, and design considerations?
A shuttle traveling at:
10,000 ipm and 300 in/s2 or
2,500 ipm and 800 in/s2?
Thanks again
Fernando
Re: Acceleration calculations
« Reply #8 on: June 02, 2006, 12:18:05 PM »
I didnt understand your suggestion of the spring at first, but now that I think of it, I beleive this is what you meant, and it makes sense.
Thanks, yet again
Re: Acceleration calculations
« Reply #9 on: June 02, 2006, 12:37:32 PM »
The cyliner needs push with at least 2X of the force that is going to be acting on the chain...  3X would be better ;)

Hope that helps
Brian
Fixing problems one post at a time ;)

www.newfangledsolutions.com
www.machsupport.com