Alignment of drive pinion to internal gear: antibacklash pinion? 1

[BirdmanofVT]

Greetings. I need to maintain a proper mesh of a drive pinion to an internal gear. The drive is low speed, high torque, and to give you an idea of size, the pinion pitch diameter is ~100mm with ~20 teeth, and the internal gear pitch diameter of ~1600mm with ~325 teeth. The drive system is stationary, meaning it does not travel with the internal gear. I am worried about the tolerance stackup and thus keeping a proper mesh. I think I have to use an antibacklash pinion. Its going to be a challenge to align the pinion even with an antibacklash pinion. I foresee needing to slot my mounting holes and using shims. Let me know if more info is needed to understand my problem. Any advice or a push towards good resources is much appreciated.

Ed

 

[diamondjim]

Can you use a 19 tooth pinion
and 323 teeth internal gear so that
the pinion teeth and gear teeth are
always at the same tooth mesh points?
You would have to use modified teeth
forms on both gear and pinion to
achieve the same center distance.
The difference in center distance is
only 2.5mm ie 762.5 vs 760mm.

You could have a second tracking pinion
with 20 teeth in your system to keep the
relative position. I assume that the
system rotates in one direction only?
How accurate does the system need to be?

 

[BirdmanofVT]

Thanks for the reply Jim.

I think I can use a 19 tooth pinion with a 323 tooth internal gear... is the advantage of this just in regard to wear, meaning, the same pinion teeth will be contacting the same internal gear teeth to limit wear? I can't imagine how that helps my tolerance stack up for initial meshing, and these gears are steel so wear isn't really an issue over time. Please clarify.

This system rotates in both directions. I meant to include that little tid-bit in my initial post. That's where the antibacklash concern comes in. From what I understand, backlash is needed to accommodate lube. An adjustable, positively locked (clamped or pinned) antibacklash gear may be an option, although it would be a pain... a spring loaded one probably isn't, as it would require a very stiff spring to resist the inertial load of this system.

This internal gear is integral to the inner race of a bearing. The backlash designed into the internal bearing is between 0.127 and 0.254 mm, and the runout with the roller path is 0.178 mm.

 

[BirdmanofVT]

From what I have read, the only issue with backlash is noise... I guess my concern should be preventing gear tooth interference, maintaining a proper contact ratio, and prevent breaking a tooth (in bending). But what I am thinking is if I stay within a backlash standard and I have a proper geometry for teeth in bending then I should be ok. I see there is a Japanese standard for backlash, JIS B. 1703-76 (for spur gears).

 

[diamondjim]

The only advantage of having the pinion
number of teeth be one of the primes for
the gear teeth is that tooth will always
be at the same place during rotation.
I think the errors in the pinion may be
insignificant to the total mesh so it may
not be a problem. I know some use a
tape around the perifery and an encoder
to track the position of the gear.
How are you tracking the position?
When the system reverses, there will be
errors if backlash is in the system and
if the tracking is based on the rotation
of the pinion.

 

[BirdmanofVT]

I will use a resolver to track the position of the pinion. I will do the tolerance study and see what my backlash is, and see how misaligned the system is, worst case. I may be all set. If not, I will repost. Thanks Jim.

 

[sg20]

In order to prevent interference you can use reduced pinion and enlarged suns. The ring gear need to shortened to be cleared of interference. I think you can find information on this subject from some of the classic gear mannuals.

 

[sg20]

In order to prevent interference you can use reduced pinion and enlarged suns. The ring gear needs to shortened to be cleared of interference. I think you can find information on this subject from some of the classic gear mannuals.

 

[sreid]

Could you consider using a Harmonic drive or a Cyclo Converter in place of gears. The backlash in these reducers is virtually zero.

 

[plasgears]

I designed a twin pinion spur gear drive that reduced the load on the alternative single pinion. I was able to justify polymer gears vs metal. These were external gears, but the same could apply to internal. Proceed with caution and attention to detail, and the twin pinions could help with backlash and alignment. Loads are shared between the pinions. Of course, the twin pinions are the result of one additional stage. A long worm drove two gears whose pinions drove the output gear.