torque calculation on a conveyor 1

[koum]

Hi!!
I have a roller type conveyor table consisting of 12 roller and i want to calculate the torque needed to move a europalet of 2000Kg weight. The conveyor's dimensions are: length=2500mm, width=1500mm. The roller dimensions are: length=2500mm, D=88.9mm. I want to calculate that torque, so as to compare it with the motor's torque and see if my motor is able to rotate the rollers or i have to get a bigger motor.
Can anyone help me??

 

[MintJulep]

T = Fr = Ma + friction

 

[STVV]

What type of rolls are you using? If they are heavy you may need to include the inertia torque to turn all the rolls. Looks like you have rolls about 98 inches long and 3.5 in Dia. If they are steel they will need to be considered. Also how are you driving the rolls. I am sure there are some configurations in your drive system that will need to be considered as well.

 

[koum]

The rolls are d=3,5 in, length= 98 in and they are made of steel tube with wall thickness 4mm. I am driving the rolls with a 5/8in chain. The motor has a 5/8in gear of 17teeth and each roll has the same gear as the motor at one end. I have a steady velocity, so a=0. Thus torque=friction=FcxMxg. Am i correct? And if so do i have to divide the torque calculated with the number of rolls? Because the torque that i calculate is much higher than the motor torgue.

 

[zekeman]

Two questions:
1) If you were doing this analytically, how did you arrive at a proper Fc coefficient? If this is existing then you can get it empirically.
2) Why do you put so much emphasis on motor torque? You pick a motor on the basis of power required, not torque. Torque is adjusted by gear ratios after you have satisfied the power requirement.

Here is what you do:
You decide the required steady state speed and the torque based on empirical data of the unit, adding the Ma effect of accellerating the unit to its ss speed ( usually not an issue unless you start-stop frequently) . Now, multiplying the torque required by the speed gives the the output power required of the motor. Then you divide by the efficiency of the gearing and chains ( I would use 65%) This gives you the required motor power, i.e. the motor size. Then you determine the gear ratio and then the gearbox or gears necessary to produce the torque with the aid of the torque/speed curve of the motor and finally the method of speed control if necessary.
An induction motor is the cheapest way if accuracy is not an issue or DC motor or servo motor with speed control if you need the speed accuracy.
If you have further question, please don't hessitate to ask.

 

[tygerdawg]

Websearch & download a PDF document called "Smart Motion Cheat Sheet". It has all the dynamics formulas for this kind of thing.

SEW Eurodrive has (used to have?) a very nice online calculator for sizing their gearmotors. One of the standard models was for a roller conveyor like your description. Select the model, plug in numbers, out pops a gearmotor selection. You can see what torque value was calculated to drive the load and the gearmotor torque selected by the program. Using this tool may require registration and download.

I imagine that most gearmotor manufacturers may have something similar these days.

You can go to most gearmotor manufacturers and download free catalogs and engineering documents for no cost. Most have your situation as one of the examples because it is so common.

In summary:
Your torque requirement will be a function of linear acceleration of mass, rotational acceleration of mass, and the torques required to overcome friction and stiction forces, gravity issues, plus some extra torque percentage for unknowns. All of that will give you a peak torque requirement.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[MintJulep]

a=0?

The conveyor will NEVER stop? When it does start, it will ALWAYS be unloaded (empty)? The power never goes out at your plant? Breakers never trip? Workers never hit the panic stop?

 

[Ross0684]

I build a lot of conveyors using 89 dia rollers,
for handling pallets various line speeds are used but just for example, with your load, say 7.5 metres per minute conveyor speed will only require about 0.3 kw to drive.
I agree with other respondents comments and notes but 30 years experience tells me that total load x 10% friction factor (for roller conveyor only) x line speed gives an accurate enough result for sizing a conveyor drive.
One always goes to the next size up anyway!!
Consider soft start equipment to take shock load out of chain, sprockets, drive etc
Ross

 

[koum]

MintJulep, i put a=0 cause is negligible. In 1 sec the motor does only 0.01m to get to ss speed.
tygerdawg, i searched on sew site but they dont have that software anymore. I called them and they said that is about 2Gigabyte and they have it only on dvdrom!! But thank you cause i found a similar program from Bonfiglioli group.
zekeman, i dont understan what you mean by torque speed curve. I calculated the power as it follows:
T=Fr=(Ma + friction)xr = (Ma + FcxMxg)xr= (2000x0 + 0.6x2000x9.81)x0.0889/2=523.26Nm (that load torque is actually the load torque at the gearhead drive shaft). So this value must be converted into load torque at the motor output shaft. So motor torque = T/i x efficiency. After i decided the required speed i found that i=35 and efficiency 0.65 as you advised me. So motor torque = 523.26/35x0.65=23Nm Taking a safety factor of 2 this torque becomes 46Nm. So the required motor power P=Txn/9550, where T=46Nm and n=N/i=1400/35=40RPM (speed at the gearhead output shaft) P=0.193Kw. I can not understand where i have to use the torque speed curve as you are advising me.

Ross0684 i think that i am close to what your experience says.

 

[dvd]

It may be worth it for you to buy a copy of:

CEMA STANDARD No. 404, "CHAIN DRIVEN LIVE ROLLER CONVEYORS"

http://www.cemanet.org/publications/index.html