Eliminating backlash in gear drives 3
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- Опубликовано: 9 сен 2024
- Input: yellow gear.
The blue gear is idly pivoted on the red gear shaft.
The pink spring loaded wedge pushes the two pins of the red and blue gears apart thereby eliminating tooth backlash between the three gears.
Wedge action keeps the zero tooth backlash very stable.
This video was made based on picture 3, page 1-48 of the book:
Illustrated Sourcebook of Mechanical Components
archive.org/de...
this also works for rack and pinion. you should publish a variant just so the channel has absolutely everything searchable
This is a similar mechanism to the double ball nuts we see on ball screws now: one nut (or gear) for each direction. So obvious once you see it. Very nice.
double ball nuts
Back lash is good or bad for gears?
In some mechanisms the backlash is necessary for them to work properly or to prevent jamming.
In some mechanisms the backlash may not be desirable, for example in dividing devices.
For more see: en.wikipedia.org/wiki/Backlash_(engineering)
Kasowanie luzu, ok. A jak z pełnym przeniesieniem mocy?
Wedge action keeps the zero tooth backlash very stable under heavy load..
The wedge is better on the driven gear?
I think the wedge can be placed on the driving or driven gear.
Usually, it is placed on the driven gear because it is larger the the driving one.
Why do two shifting gears need to be used to eliminate backlash? Why can’t one gear be made with perfect spacing?
The reason why backlash exists is due to tolerances between mating surfaces. It's impossible to have perfection; this is why backlash exists.
Probably due to the cost of high precision engineering where this is a cheaper fix, also makes up for teeth wear
There is no substance that can move against another surface without wearing out unevenly. There is also no perfect manufacturing process that does not produce minor variations.
You would be trying to hit a moving target due to wear.
Backlash for gears is generally compensated 2 ways, meshing the teeth deeper into each other or using 2 pinions in tandem.
Both will increase wear/friction in the system.
In long linear travel applications or dirty conditions, gear rack and pinion is much better than a ball screw. No whip, less pitch error, essentially no stretch, less moving parts, cheaper, simpler, obvious when dirty, etc.
Suppose we laboriously manufactured such a perfect gear: it wouldn’t run for very long before natural wear between the surfaces caused minor deformations on the mating surfaces that either introduce backlash or, more likely, cause the gears to seize up and stop moving. For this reason we do the much cheaper thing and just engineer in some allowances between the surfaces that create a tiny bit of backlash. That backlash can be eliminated by introducing controlled compliance (springs/elastics) elsewhere in the system.
This is great for high torque, but under high speed this feels like a bad idea
The vibrations would get rough due to the mechanism being on oneside of the shaft. If instead of one big wedge, there were five smaller ones equally spaced around the shaft, it would probably work in high speed sictuations. Could set it up like an iris mechanism.
@@Superwoodputtie ooh, easy fix and minor difficulty
Now I'm going this video is remade and we get a v2 with that design
Re it being good for high torque: If the force on the sprung gear exceeds the spring, then wouldn't it start to be much less effective?
Someone said this setup is used in radios where precision is important but load is very light.
@@lctsi So a wedge works like a lever. The load that gets transmitted from the pin to the wedge is divided in two parts. One acts on the side of the wedge, the other part tries to push the wedge back down.
If a wedge has an angle of 45 degrees these two force (side and down) are equal. If the angle is 22.5 the down force is 1/2 of the side force. 11 degree, the force down is 1/4. 5 degree wedge the force pushing the wedge down is 1/8 of the torque. (I dont think wedges under 5 degrees are very effective, so we'll stop here)
So whatever your torque, the spring only has to hold 1/8 of that force. Which helps a good bit.
It's not included in this demonstration, but if there were a locking nut that held preasure again the spring, you could set a "preload" on the spring. So it only takes 5N of force to remove the backlash, but you add another 25N of preload.
On a 10cm (5in) gear this would allow you to have 200N-M of torque (150 ft-lbs)