Zero backlash worm gear idea.

[ynneb]

Afters Andys request, It has made me think about how to make a zero backlash worm drive.

As I have found in the past, you think you have a good idea only to find that it has already been done.
B4 I spend time drawing up this idea, does any one know of a zero backlash worm drive? Do they already exist?

The beauty of my idea is that it does not rely on fine tolerance machining.

[Torsten]

Well lets hear about it, I have some dought that this is possible.
There are two kinds of frictions in a power transmission rolling and
sliding friction where rolling is clearly the lower and better.
A wormdrive is the worst of all with the sliding friction been the
dominant part of transmission.
Reduceing clearance or even preloading would significantly increase
the friction produced.
One way could see this happening is with the large wheel having
roller bearings with radiused running surface mounted perpendicular
to the shaft instead of the teeth.
Each Tooth would be replaced by two bearings slightly offset one making
contact with front the other back side.
The bearings would need to be very small in order to be able to have
tree teeth of the worm engaded at all times.
The precision involved in making this would be outside of the abilitys
of most hobby shops and likely be expensive as a industial product.
Unless its mass produced of course.

[sbrpollock]

Benny:

I remember reading an article somewhere about a type of zero backlash worm drive that uses the same principal as a ball screw. It's not that both gears have grooves. The two gears have teeth that mesh with a ton of backlash, then several sets of captive balls are run between the contact points of the teeth.

I know I read about this (The article had pictures) long, long ago; even before the World Wide Web. To be honest I think it was in the same article where I first heard of ball screws. It was in a "Popular Mechanics" or "Popular Science" type of magazine. I know when I read it I thought "This will never take off", but then again, I also said "This will never take off" the first time I saw a color computer!

[ynneb]

I will do a drawing of what I am thinking about, but in the mean time I will try to verbally desribe it.

Image you the worm wheel is split in half. The split is vertical, so esentally you have two thin wheels when they are taken apart. when the wheels are put together they form a working worm wheel. There is a spring inserted in the assembled wheel that forces the two halves to be rotated a few degrees out of sync from each other.

When the whole assembly is put together, it will put a load on both sides of the screw. This will illiminate any backlash. I guess the comprimise is that the pressure put on the screw would be increased a lot. The other thing is if you have and exsessive load to drive the spring load must be greater than the load the assembly is driving.

One advantage is when either the wheel or screw wears down, the slack is taken up by the springs.

I dont know if this description is clear. I know it will be hard to draw, but I will give it a go.

[HuFlungDung]

Benny, there is a manufacturer who has stolen your idea and put up a website about it already

http://www.logan-mmk.com/zero_backlash.htm

Somewhere, sometime, I also read about another design that incorporated sort of a cam-roller stud design for the worm wheel (like a starfish) and a special worm thread that accepted these roller tips.

[ynneb]

Thats a bummer.
One of these days I will invent something that is completely new.

These days I have stopped getting excited about my ideas, 4 point something billion people in this world, someone surely must have had the same thoughts.

[lerman]

Years (actually decades) ago, I saw zero backlash worm gears used in radio tuners. They consisted of two thin gears mounted on the same shaft with a spring causing them to be forced to rotate in opposite directions relative to each other (just a few degrees). They meshed with a single worm.

One of the gears was screwed to the shaft. The other just applied pressure against the worm.

Ken

[WayneHill]

Originally Posted by lerman Years (actually decades) ago, I saw zero backlash worm gears used in radio tuners. They consisted of two thin gears mounted on the same shaft with a spring causing them to be forced to rotate in opposite directions relative to each other (just a few degrees). They meshed with a single worm. One of the gears was screwed to the shaft. The other just applied pressure against the worm. Ken

http://www.antibacklashgear.com/

[Torsten]

Originally Posted by ynneb I will do a drawing of what I am thinking about, but in the mean time I will try to verbally desribe it. Image you the worm wheel is split in half. The split is vertical, so esentally you have two thin wheels when they are taken apart. when the wheels are put together they form a working worm wheel. There is a spring inserted in the assembled wheel that forces the two halves to be rotated a few degrees out of sync from each other. When the whole assembly is put together, it will put a load on both sides of the screw. This will illiminate any backlash. I guess the comprimise is that the pressure put on the screw would be increased a lot. The other thing is if you have and exsessive load to drive the spring load must be greater than the load the assembly is driving. One advantage is when either the wheel or screw wears down, the slack is taken up by the springs. I dont know if this description is clear. I know it will be hard to draw, but I will give it a go.

Yes that is how it is done on regular gears too.
Another option would be to split the driving screw.
Instead of been one long thread it could be split with
a slight gap just over the center portion of the wheel.
If this gap could be adjusted you could take out the lash.
Because it is further away in the gearing transmission the
spring load could be less then what would be required when
splitting the worm wheel.
Ether way you will reduce the active surface area used for
the driving pressure by half.
This should be considered in the design of the wheel and its
contact areas.
Just simply modefying a existing wormdrive would lead to much
reduced loadratings.
I would love to hear from somebody that has actualy done it and
can tell about the results obtained / is it worth it?
Good Luck

[Clementvs]

Hello Torsten,

It seems this product exist for decade already. it's made in germany. I know rotary table manufacturer that are using it to get the highest precision possible.

You may find information and drawbar on Allytech's website (it's a ".eu")

http://www.allytech.eu/index_fichier...dwormwheel.htm

to have better accuracy and power transfer they do make high teeth. there for the line of action seems to be very good.

Hope this helps

[handlewanker]

Hi, time to think outside the box......why use a worm drive?........to get the low ratio or as for a dividing head or rotary table the division ability.

You can also use a compounded set of gears meshing together that provided they are meshed tightly will give practically backlash free drive.

I once toyed with a design for a friction free worm drive that had a series of ball races place around the periphery of a worm wheel in place of the teeth, and these engaged with the worm shaft between the flanks of the worm.

The faces of the bearings were to be curved to allow the meshing with the worm shaft, much like the involute curve of spur gears.

That is as far as it went, paper engineering....LOL.
Ian.

[Clementvs]

Hi handlewanker,

I think the advantage of the wormgear is also to drive a high torque with précision.

However, in some case you may need high speed rotation then precise move or position. This is supposed to be torque motors specificity, how ever on the same system the system I talk in my latest post it's possible to make speed variation with a worm gear (actually it's dynamic backlash variation to allow important shaft rotation change.

you can visite http://www.allytech.eu/index_fichiers/OTTMATIC.htm