All,

Cyclo speed reducer is different kind of animal as far as failures are concerned. For example, sometimes they fail to transmit torque with no obvious visible failures once opened or any symptoms in vibration data.
Here is cyclo drive operation concept

I, and possibly others, will be interested in the experience you guys may have and willing to share as far as failure modes, vibration signature, etc. are concerned.

Thanks,
Dave

Morning Dave
We have quite few of these units anf for the most part they are fairly bullet proof. We monitor mostly with oil analysis. The problems that have occured on the vibe end have been entirely with the high speed end (input) of the unit and that being the a bearing failure with typical bearing fault signatures.Also to note this failure was caused by a seal that went bad and allowed the oil level to drop to the point the high speed unit was not receiving the correct amount of lubrication.The seal in this case was replaced and the oil level topped up and about a month later the bearing went into failure modewith about a one week life span before the input unit had to be changed.

Dave,

I have rebuilt and monitored many of these drives and can second Lee's assessment that they are fairly bullet proof. I have seen a few failures on the high speed end like Lee describes and they have all been due to seal failure, usually as a result of misalignment and/or coupling damage. Other failures have been in the eccentric bearing and they will produce a high 2 x running speed. I have had another where most of the oil had been displaced by water. Other than some corroded pins and rollers, there was really nothing wrong and it went back into service for another several years.

I cannot imagine a situation where they would not transmit torque without some obvious damage. Can you explain further?

I agree, cyclo reducers are pretty robust and if bearings are holding up, the whole thing works fine.

I am not sure that they in fact fail to transmit torque. That is what night shift mechanics report in the morning. Checked by hand the "failed" cyclo appears to be working, at least with small load. As I said above, nothing obvious is found when the box is opened up. In other cases the VFD trips out intermittently and once cyclo is replaced, the problem won't come back.

Of course, this approach is not a solid prove of a failed cyclo but that is how troubleshooting process works probably in many places.

Sometimes there is a troubling symptom in the vibration data but it is hard to assess its severety. Attached is an example I would like to share.

Note, overall reduction is 21:1 ( likely, it is a single reduction cyclo). PeakVue spectrum shows clean high magnitude orders of 21 x output shaft speed, which obviously is speed of the input shaft.

Likely, it is a result of improper cam action: friction or impacting should not occur if the cam is well lubricated and not worn out.

Dave

This message has been edited. Last edited by: David_G,

Cyclo_reducer.doc (54 Kb, 40 downloads)

Dave,

I'll look back and see if I can find a spectrum of a one that was taken out of service and called bad. I never got to see it first hand but it sounds like you have the same night shift mechanics.

It's not really a cam but an eccentric roller bearing with the center of the disc being the outer race unless they have changed the design since their 3000 series.

21:1 is a single reduction unit. Double reductions are really just two single stages bolted together.

Here is one that I pulled out of service, and there was no visible damage anywhere to be found. This is a 6:1 double reduction.

Edger_Outfeed_Belt_w_Picker.doc (346 Kb, 59 downloads)

Wsegrav,

Data certainly suggests a fault inside the cyclo. Impacting and modulation warrants this assessment. I assume that bearing fault was ruled out. Not naving a cursor makes is hard to narrow down the problem, but it has been apparently done. The hard piece to me is to assess any problems which have been developed in the cam (ring). I believe the problem is in there, it is just hard to see it with a naked eye.

Were there any other operational symptoms suggesting a fault?

David

Growling noise.

There should be a problem with this cyclo!

What does this series of harmonics, family of sidebands points to? I guess modulation occurs at the running speed.

My first guess would lean toward torque oscillation that loads/unloads the Cyclo gear causing gear chatter. This might occur at low load with friction issues with the conveyor or whatever is being driven by the Cyclo. My second guess would be poor lubrication possibly combined with overload. Both of these guesses could be confirmed by discussion, inspection, or further measurements such as vibrations, torsional vibrations, motor current analysis and temperature.

Some say the obvious can be right in front of you!

Walt

wsegrav
what we found to confirm what Walt said was when the lube level was low this starves the input side first and does cause a lot of noise in this location so it is possible that is could be a lube issue.

quote:

Originally posted by Danny Harvey:
It's not really a cam but an eccentric roller bearing with the center of the disc being the outer race unless they have changed the design since their 3000 series.

Thats one of the main nitpicks I have with the cyclo - their use of OEM special bearings, etc which cost a fortune (comparatively) when you go for rebuild. In my experience, the Rexnord Planetgears have been an exceptionally robust drive with virtually no issues at all, even when undersized for the application. The bearings/seals are generally so common that many mills that run them might even have them in stock for other applications and not even know it.

The only special bearing is the eccentric. I don't know of any other place to get them except from Sumitomo and they are right proud of them.

I doubt if gear chatter is a problem, since there are no gears though.

I forgot that I promised to post some data on this subject. I'll try to remember next time I have my laptop set up which will be this pm.

Danny,

I consider that the Cyclo has a "gear-like" mechanism and therefore could be susceptible to backlash from torque reversals. I don't have a Cyclo case history to substantiate this hypothesis. It would simply be on my check list for evaluating a "growling" sound in a gearbox, since I have encountered it on other gearboxes.

Walt

I am attaching a PeakVue spectrum and time waveform from a Cyclo reducer that was "shot". Unfortunately I got no more information on the nature of the failure than that.

Walt,

I would guess that gear chatter due to backlash is created by the teeth bouncing back and forth from one tooth to the next. Since there is no such "capture" in the cycloidal disc I don't see any mechanism that could create chatter. I would suspect that a growl would be due to corrosion or wear in the pins and rollers on the output shaft. Like you, though, I only suspect this because I don't really have anything to confirm it.

I have disassembled and repaired quite a few of these things and found that most failures are in the eccentric bearing and most often due to corrosion. That may be because most of the ones that I repaired came from papermills but they are also widely used in manufacturing of oriented strand board and the eccentric was usually the cause of those failures too.

Maintain the integrity of the shaft seals, use the recommended oil and change it per recommendations, and use a washdown duty breather in wet areas and they will last a long, long time.

Also, this type of drive is inherently very low in backlash by design without modification and only requires minor modification to make it 0 backlash which makes them very popular in robotics. They do, however have minor oscillations in speed. I can't remember whether this is due to the eccentric bearing or the cam action or the waves on the disc as they pass over the rollers but if they are used on paint lines, there will be a resultant wave in the paint thickness.

cyclo.doc (59 Kb, 31 downloads)

quote:

Originally posted by wsegrav:
Growling noise.

What i've seen is they tend to get a general raised noise floor similar to cavitation when they start to wear out. Otherwise oil is the best monitoring method i've found.