Ballscrew Torque/Force

Hi guys.


I have a piece of kit that we can call a press. It's a piece of metal block moving up and down.


The setup is:
MPL-B420P
Kinetix6000
gearbox 4:1 + ballscrew 10mm lead/40mm Diameter



What I need to know is what force that is applied to a product when the block is in it's bottom position.


Atm all I'm reading is a torquefeedback. As I understand let's say 50% readeout equals to 50% of 4.74Nm (ref toruqe) on the shaft. Because I have the ballscrew I'm using equation.


F = T x 2 x Pi x gearbox ratio/ lead x eef


so 50% of torque [2.37Nm]

therfore:
F = (2.37*6.28*4) / (0.01 * 0.9) = 6320N

Does it sound about right, looks a lot to me ?



Cheers

Yah that formula is based on conservation of energy, so, assuming the units are self-consistent, it should be correct.


Numerator: 2.37 * 6.28 * 4 = (2.37 * 4) * 6.38 ~ 10 * 6.28 ~ 63


Denominator: 0.01 * 0.9 ~ 0.01 = 1/100.


63 / (1/100) = 63 * 100 = 6300, so anything near 6k (6,000) sounds reasonable.

Lower efficiency means more force?

L D[AR2 said:

Lower efficiency means more force?

Click to expand...

yeah, that is odd.


wiki has the efficiency in a product with torque.

Equation don't look right.


If effiencys is decreased also torque should decrease.


Thinking that equation should be

F(Nm) = Gearbox * T(Nm)*2*3,14* eff /lead







F = 4* 2,37*2*3,14 * 0,9 / 0.01m = 5358 Nm

Lare said:

Equation don't look right.

F(Nm) = Gearbox * T(Nm)*2*3,14* eff /lead

Click to expand...

Thanks, Force is in N though


This makes sense

Whether the efficiency exponent is +1 or-1 with respect to either torque or force depends which is driving the motion.

E.g. a ball screw raising an elevator/lift car would have efficiency multiplying torque or divided into linear force (weight plus any acceleration).

That same ball screw lowering the same car would have efficiency divided into torque or multiplying linear force ) weight etc.).

drbitboy said:

Whether the efficiency exponent is +1 or-1 with respect to either torque or force depends which is driving the motion.

E.g. a ball screw raising an elevator/lift car would have efficiency multiplying torque or divided into linear force (weight plus any acceleration).

That same ball screw lowering the same car would have efficiency divided into torque or multiplying linear force ) weight etc.).

Click to expand...

That is true.


But according OP this is press. If screw itself don't have much weight we can assume that it don't make much difference to effiency. (+ Kg (Or 10*N) to force on pressing down).


Effiency of gearbox isn't taked account either on equation.

If gearbox effiency is 0.9 then



F = 0,9*4 * 2,37*2*3,14 * 0,9 / 0.01m = 4822 N


Or googling gives a lot of different calculators for checking own calculation.

For force (Horizontal, but for up/down if no weight.)

https://www.lintechmotion.com/sizing1.cfm
https://www.lintechmotion.com/sizing/Thrust-Force/thrust-inputs.php

It gives before gearbox 1340 N
-> *4*0.90 = 4822 N

Lare said:

That is true.

But according OP this is press.

Click to expand...

Good point.


With the elevator, only as an example of where efficiency should be in the formula, I was assuming the ball screw is always supporting the weight of the car i.e. the ball screw force on the car is always upwards, and the car is never pulled down by the ball screw (or pushed down, as I suppose the motor could be above the car).


On the press, the ball screw would, I assume, do both i.e. exert force in both directions: exert downward force when the block is pressing onto the product; exert upward force when lifting the block away from the product.

gearbox efficiencies can be missleading. They are usulally quoted as a pecentage at full capacity in power. In reality, there is a staic friction and a dynamic component.

Do you also need to considder the inertia of the press acting on whatever it comes into contect with? Depending on the mass and velovity this could be significant.

Nick

https://www.engineeringtoolbox.com/screw-jack-d_1308.html

The torque on the screw will be the motor torque times the gear ratio times the efficiency.

Don't expect a dead-nuts correct answer. Friction and efficiency vary and are approximations. The ball screw efficiency is going to be around 90%.