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Belt and Pulley

Belt and Pulley

Belt and Pulley

(OP)
Hello,

Suppose this pulley is latched to a motor's shaft residing on the floor. On the ceiling there is a similar pulley hanged on a hook. At the center of the belt's height there is an object carried by the belt. When I ran the motor sometimes the belt's teeth does not lay on the pulley's groove which causes the object's position to not be coherent with the motor's rotation. I tightened the belt and the problem still comes from time to time? The motor is moving forward and backward.

is there any idea how to solve this problem?

Thanks

RE: Belt and Pulley

You need to provide a better description, perhaps with pictures/drawings of the overall set-up before anyone could give you any idea what to look for.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

RE: Belt and Pulley

(OP)
Hi John,
Here is a drawing.

RE: Belt and Pulley

What is keeping the belt in contact with the "object". What is the object? We cannot guess.

STF

RE: Belt and Pulley

how about using outer idlers to keep prevent oscilations in the belt causing it to jump a tooth.

RE: Belt and Pulley

(OP)
Hi Byrdj,
Thanks it's a good idea.

I added the bottom roller only, where the motor pulley. But I did not add the top one. By the way the upper pulley
has no teeth, it's a roller. But the motor pulley still skips the belt teeth sometimes and as soon as start skipping it stays doing it.

RE: Belt and Pulley

(OP)
Hi SparWeb,

The object is a trolley. Both belt ends are fasten on the trolley. The trolley carries 10-20 lb rod.



RE: Belt and Pulley

You need to guide the carriage; you can't rely on the belt to do that.
Unless you need the carriage to move _very_ fast,
you need a gearmotor, and/or a variable speed drive.

If there's any risk of anyone getting hurt, and it sounds like there is,
you need to get an actual engineer involved.





Mike Halloran
Pembroke Pines, FL, USA

RE: Belt and Pulley

(OP)
Hello MikeHalloran,

Yes I'm using a gear with a variable speed. The speed plays role in the problem occurrence. It takes more than 3 hours ,continuous running, before the problem occurs. As soon as it occurs it keeps continuous occurring. The trolley out of sync with the motor rotation.

Thanks.

RE: Belt and Pulley

Perhaps you need two outside idlers at the bottom - one each side of the motor pulley. There are really only two possibilities for your failures:
1. Belt oscillation during rapid travel is allowing a "slack" wave to ride around the motor pulley.
2. The belt is under-rated for the loading applied.

Either way, two idlers at the drive pulley will help by increasing wrap angle on the drive and isolating it from oscillations.

je suis charlie

RE: Belt and Pulley

(OP)
Thanks gruntguru , I will consider it.

RE: Belt and Pulley

Sounds like it might be a heat problem which could cause the belt to stretch to the point where the lugs on the belt no longer match the grooves in the pulley. Have you considered replacing the belt/pulley combination with a chain/sprocket scheme?

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

RE: Belt and Pulley

(OP)
Thanks JohnRBaker. I'm getting ideas to solve it. I'll consider it.

RE: Belt and Pulley

If the belt is tensioned properly, and if the object's weight isn't enough to cause the belt to slip, the next most likely condition is that you have mismatched tooth profiles. There are numerous different tooth profiles in use around the world for different purposes and it is a very common problem to end up with a belt of one profile and a pulley of a different (but very similar looking) profile. Google "synchronous belt tooth profiles". Mismatched profiles will eventually jump. I have seen it many times. Carefully double check the exact profiles you are using.

RE: Belt and Pulley

(OP)
Thanks Jboggs, I'll look at that.

RE: Belt and Pulley

Omar,

Adding onto the excellent suggestions posted above, have you run through the process of sizing the belt - selecting the profile and width? Some of the newer profiles such as the GT2 etc. are better at resisting slippage than the trapezoid types. What is the distance between the drive pulley and the idler pulley? How many teeth do you have in contact on the drive pulley? What are your torque and power requirements?

I would recommend contacting some of belt and pulley manufacturers to get their input as well - Gates and York Industries are a couple that come to mind. I would also recommend using a timing pulley at the top idler position since there are teeth riding on it. It will be quieter and is more appropriate. If you do use a timing pulley at the top, make sure your are spaced an integral tooth count apart. You can use smooth rollers as tensioners since they are running on the back side of the belt.

Kyle

RE: Belt and Pulley

Tooth jumping is a common problem on long belts. You have to use idler pulleys on the back side of the belt near to the toothed sprocket.

RE: Belt and Pulley

The unloaded section of belt in this arrangement is the bit that sits between the load and the driving pulley. The logistics of constraining that section to stop it flopping about and feeding oscillations onto the pulley are complicated by the fact that the load is moving through the space you're trying to control. Moving the motor to the top would avoid that issue by moving the slack to the back of the belt - a section which is constant in length and amenable to the addition of idlers - you are better able to judge than us whether that's a viable change.

Do you know whereabouts in the stroke of the system it starts to skip? If it happens at the bottom, it could just be the stretch in the belt feeding too much slack into the drive pulley. If you think this is happening, you might add a tensioning spring to the belt attachment on the bottom of the platform.

A.

RE: Belt and Pulley

(OP)
Thanks very much for all participants. I hope all thoughts would help me overcome the problem.

RE: Belt and Pulley

(OP)
Hi all,
I have to add this.
The post that carries the trolley between point A and B is not perfect, straight. The distance between A and B is 300 cm.
When I put a laser light at point A to pint at the wall, by the time the trolley at point B, the laser light deviated by 15 cm.
The light should remain vertical " perpendicular " , at right angle.
Distance from A to B = 300 cm; deviation ~= 15 cm.


RE: Belt and Pulley

What is your question?

RE: Belt and Pulley

(OP)
The belt between the two pulleys is not perpendicular. We used two rollers at the bottom end of the post to line up the belt before entering the pulley's groove. Since the belt is not perpendicular, would this situation cause a problem after a while of service?.
By the way, I'm an electronic engineer working with a mechanical engineer.
Thanks

RE: Belt and Pulley

Does anyone there have a phone with a decent camera in it?

Mike Halloran
Pembroke Pines, FL, USA

RE: Belt and Pulley

(OP)


Hi All,

We tightened the belt but from time to time the belt slips and causes a displacement to the trolley.
The pulley is on the motor shaft . On the other end of the belt is a roller. The two rollers near the
pulley to guide the belt and forbid the belt vibration. Any idea how to stop completely the belt slipping.
I attached a picture for the material.

Thanks
-Omar

RE: Belt and Pulley

We need a picture of the installation, not the loose parts.

RE: Belt and Pulley

(OP)
Hi 3DDave,
The installation looks like the picture in the previous post.

Thanks

RE: Belt and Pulley

Quote:

The belt between the two pulleys is not perpendicular.

That alone bodes ill.

Did you read the engineering section of the belt supplier's thickest catalog? You should.

Or search for 'mule drives' or 'Corvair fan belt problems'.

Mike Halloran
Pembroke Pines, FL, USA

RE: Belt and Pulley

A diagram isn't the same as a photo of the installation.

RE: Belt and Pulley

What kind of accelerations is the belt seeing in starting and stopping? Is it a steady even accel/decal or is it jerking? Sudden starts and stops can cause belt slippage.

RE: Belt and Pulley

(OP)
Thanks for all participants.
We are looking for the cause, sometimes the pulley skips the belt during motion.

@MikeHalloran
Your idea perpendicular and looking at belt supplier's thickest catalog are good thoughts.

@Jboggs:
Same accel & decel.~0.43 rev/sec^2. & velocity is 40 rev/min. However, the belt sometimes skips
during motion.

RE: Belt and Pulley

I would, as suggested above, use a stiff spring under tension to mount the top pulley. Or alternatively use a torsional spring forcing an idler pulley against the back of the belt at the top to keep the belt tensioned during the accelerations.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Belt and Pulley

As suggested above, it is time to post some actual photographs or at least semi-accurate drawing. You have invested a lot of typing here when a few good pictures would answer a lot of questions.

Can you provide the actual spec on the belt (not just some generic description)?

RE: Belt and Pulley

Hello,

I would suggest changing from a trapezoidal tooth shape to one of the GT2 type belt configurations. I recently redesigned a belt drive somewhat similar to your application that used an L profile timing belt that skipped teeth under load. I switched to a 5mm GT2 design and also revised the tensioner idler to increase the wrap angle around the driving pulley. The increased number of teeth in contact dramatically reduced the tooth slippage problem. I agree with the other posts regarding idlers. You could be experiencing slippage on the slack side of the belt and as you mention, once slippage starts, it continues.

Regarding the post you mention, how are you guiding the trolley? Do you have shafts to maintain orientation of the trolley?

We really need to see some pictures of the assembly.

Kyle

RE: Belt and Pulley

(OP)
Thanks for all,

@itsmoked

Similar to your suggestion, we tighten the belt. Great idea.

@kjoiner
What you suggested were done except changing from a trapezoidal tooth shape. We are planning to change to MTD (Metric Round Tooth).
how are you guiding the trolley? wheels on the corners.
Do you have shafts to maintain orientation of the trolley? Yes

For now we are using a trapezoidal tooth shape, with high tension on the belt. More than 36 hours passed and still working without
any slipping.

RE: Belt and Pulley

Hi Omar,

"What you suggested were done except changing from a trapezoidal tooth shape. We are planning to change to MTD (Metric Round Tooth)."

I've seen the MTD belt profile. Just make sure you are staying within the allowable specs for the belt. Also, make sure the tension in the belt is not going to cause excessive overhung loads on your drive train components, especially the plastic idler pulley at the top. Have you run through the design process for sizing the belt based on your loads. If not, York industries has a good design guide.

http://www.york-ind.com/

http://www.york-ind.com/York_ify_3.pdf

"How are you guiding the trolley? wheels on the corners. Do you have shafts to maintain orientation of the trolley? Yes"

Yes, we have two shafts running vertically along side the "box" we are moving up and down. The box has sets of rollers at each corner. At each corner there are two rollers. On the left side, the rollers are machined in sort of a spindle shape to surround the shaft and locate the box. On the right side, the rollers are similar but don't surround the shaft. They just keep the box located. I would show pictures but this is a part of a patented product. We originally tried using self aligning plastic bearings (like Igus) but the rubbing motion set up vibrations and made noise.

Kyle

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