Pulley System

[Kazuaki]

Hi, I am working on a rope drive system that threads sheets of paper through machines. I am trying to calculate how much horsepower the motor requires to do this. As of now I have a value of 300 hp for the motor and I think this is a bit too high. Can you guys give me some tips on how to solve this problem.

Thanks

 

[desertfox]

Hi Kazuaki

Can we have the technical details ie:- size of rollers, number of rollers, and details of the rope drive ie ratio's etc and then I may be able to help you.

regards
desertfox

 

[Kazuaki]

The ropes are driven by one big pulley guided by many smaller pulleys, powered by an electric motor. There are no rollers to speak of so the only thing the motor needs to spin are the pulleys (in addition to the weight of the pulp paper).

 

[gcaudill]

Two ways to approach this problem come to mind.

1.) Calculate the amount of work to be accomplished by determining how many pounds/minute of paper that must be moved. See if you can correlate this to a HP by some creative thinking.

2.) Consider tension or compression forces (which ever the case) required to pull or push the paper and convert that to HP based on speeds, forces, RPM's, etc.

 

[Anthonyr]

The HP equation in the form FORCE x VELOCITY/33000 may be the best one to use. FORCE is in pounds and VELOCITY is in feet per minute. If you can determine how much force is required and then the speed at which the paper is threaded, the HP can be determined with the above equation. I would also apply some type of service factor on top of the HP calculation to size the motor.

 

[Kazuaki]

This is what I did:

1)Calculate I=0.5mr^2 for each pulley
2)Added up all the I
3)Calculated acceleration for each pulley
4)Calculated required torque using I X acceleration =torque
5)Divided torque by the radius of the pulley (to get a force)
6)used hp=FV/33000 to get my horsepower

 

[ivymike]

Why are the pulleys accelerating?

 

[GregLocock]

Because they are in the Earth's gravity? Of course it depends which inertial reference frame you are in... Cheers

Greg Locock

 

[Kazuaki]

The pulleys are accelerating because the ropes are being guided by them.

 

[ivymike]

...and the ropes are accelerating because...? I must be missing something. Does this machine continually speed up and slow down?

 

[Kazuaki]

The ropes accelerate because two ropes pinch together to grab the sheet of paper. Where it then threads it through the entire machine.

 

[ivymike]

You don't happen to have a picture or sketch that you could post for us to take a look at, do you?

 

[ivymike]

Just to check that we're using the same terminology, when you say that the pulleys are accelerating, you mean that each one is spinning faster and faster about its own axis, right?

 

[Kazuaki]

I do not have a picture of the system, but to answer your question, yes the pulleys are spinning faster and faster.

 

[boo1]

I though Acceleration was for start up not steadt state condition!