I'm working on a project where I need a gear with the advantages of the
harmonic drive gear. However, I understand that these are fairly expensive.
I need 1000 gears, and I consider how it can be made cheap. Can they be made
in plastic? The original harmonic drive patent is from the 1955, are there
any new patents protecting it?
What other kind of gears are typically used for industrial robots?
There are less sophistocated versions which would be far easier to tool up
for those numbers, see:
Yes plastic is OK, depends on load and allowable design clearances, I have
made a huge rotary table drive using waterjet cut 50mm sheet acetyl using
similar geometry. In my case the low tip (contact point) load of this
general design made plastic workable for the torque required. Waterjet
cutting tolerances (about 0.2mm if I remember correctly) was good enough, I
think we had the parts assembled and running the day after the parts
Thank you Mark.
This is indeed a very interesting gear. What was your motivation to use this
type of gear? If you have any pictures or cad files of your gear, I would be
very interested in seing them.
that was many years and several computers ago, I do remember drawing the
cut curves for the rolling element in Acad but I no longer have the file.
Shouldn't take too much work to draw, even if you have to manually
translate/rotate the elements to define the "ring gear". The turntable
itself no longer exists, although I would have liked to recover the gearbox.
Reason to use this design was firstly because it met load requirements
within a reasonably narrow available space (the case was about 800mm dia x
about 120mm high). Second (very attractive) reason was it's easy to make one
off, we used off the shelf needle roller cam followers and a heavy ball
bearing for the eccentric on the input shaft. The rolling element (ring
gear) was from 50mm sheet acrylic like I said, and the case was fabricated
from plate stainless steel (the environment was mildly corosive).The case
incorperated a large slew ring bearing, there was no output shaft, just a
flange which carried the driven rollers. I think the ratio was 30:1.
The only worry I had at the time was lubrication, the ring gear doesn't need
it but the cam followers and main bearings did, but I didn't want oil around
the acetyl ring gear. The speed was quite low so we found a reasonably
compatible grease for the needle roller cam followers and used fully sealed
deep grove ball bearings for the shafts.
Hope that helps,
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