Gear for articulated robot, harmonic drive?

Hi, 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?
Kristian Kassow
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hi Kristian, There are less sophistocated versions which would be far easier to tool up for those numbers, see: http://cyclo.shi.co.jp/eng/product/gmoter/saikuro6000/index.html 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 arrived.
Luck,
Mark.

expensive.
made
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
Best Regards
Kristian

there
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hi Kristian, 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,
Mark.

the
be
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.