Eliminating backlash of rotating mechanism with unbalanced load 1

[AS_HCS]

Hi Everyone,

We are designing a machine which has a rotating load that is rotated by hand wheel. The shaft has 250kgs on 1 side and then 300kgs on the other side as shown below.

It will be rotated by hand wheel 180degrees and then the load changes so that the extra 50 kgs is on the other side and then the loads is rotated back.

We have tried a gear box and this works when the rotation of the load is working against gravity but when we go past the Center of gravity and the load is working with gravity - we get what I believe is backlash in the gearbox (the load bounces around).

We need to eliminate this backlash - we dont have to have a gear box if there is another method but is there a way to eliminate the backlash?

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[3DDave]

Buy a better quality gearbox?

The main problem is that in the case you don't like you have an overrunning load - the load is trying to drive the gearbox ahead of you turning the hand wheel, so it is sticking and then slipping. You can help by making the rest of the device much stiffer or maybe by using a better lubricant or by using a better gearbox that doesn't have as much force gap between stick and slip or as much backlash.

This article suggests using a gear with a higher helix; this is a lower reduction ratio.

https://www.imousacorp.com/2021/07/15/stick-slip-effect

Assuming the rotation would move very freely rather than hanging up - if it can hang up then the worm moves the wheel until enough force builds to make it come loose - it then moves forward to contact the other face and stops. Friction in the rotation bearing then holds it in place. The crank then moves until all the backlash is gone again until the force is enough to pop it loose again. Unlikely, but it is also a cause.

It may also be a badly made gearbox.

 

[TugboatEng]

In the marine industry industry I have seen "detuners". They are a spring loaded feast installed at one end of the pinion to pin it against the bull gear. Motorcycles Doo something similar.

Do you need to eliminate backlash or simply maintain a maximum amount? Angular contact thrust bearings are a first step as they allow operation without bearing backlash.

 

[desertfox]

Hi

Take a look at this webpage

https://www.newequipment.com/plant-operations/article/21276537/achieving-zerobacklash-wormgear-pairs

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[MintJulep]

This is not backlash.

More likely, you are operating right on the border of the worm-gear being locking vs. non-locking. Once it starts, the bouncing causes a transition between static and dynamic friction, and whatever elasticity is in your system keeps the cycle going.

https://www.motioncontroltips.com/when-are-worm-gears-self-locking-and-where-is-this-useful/

If you can get a gear box that is clearly in the self-locking range for you load, this probably won't happen.

Anyway, you probably shouldn't rely on self-locking as a brake, so a separate brake would be better, and that would allow you to use other types of gearboxes.

 

[dvd]

What is the bearing arrangement? There may be other issues than gear reducer. Give some better background, please.

 

[BrianE22]

Is this continuous rotation or "back and forth"? If "back an forth", then I think preloading with a spring would do the job. Mount the torsional spring on the output of the gearbox and preload it so torque won't change sign.

 

[CWB1]

Not to nitpick but its critical to understand that in reality you cant eliminate lash, only minimize it, and to do so you must understand part tolerances and where gaps exist between parts. Some gearboxes are fully adjustable so you can change the gear mesh depth and other variables that affect lash.