Plastic Harmonic Drive Gearing?

[jstewart]

Hey all,

I'm looking at an idea for a step-up transmission with a ratio around 30:1 - 50:1. The input speed (the low-speed side) is slow, about 100 RPM. The torque required is about 500 inch-pounds, fluctuating (and reversing). Because of the reversing torque, the transmission would need to have minimal backlash, so that brought harmonic drive gearing to mind. There isn't really a requirement for tight positioning, so the "squishy" on-center stiffness probably isn't a big concern.

My company would build about 40,000-60,000 units a year, in a highly cost-competitive market, so I was thinking that custom molded plastic components might be the way to go. I don't have any tight packaging requirements, so the size advantage of metal gears wouldn't really be needed.

My preliminary search for manufacturers of harmonic drive gearsets didn't turn up anything except for the metal versions used in robotics. There is a German startup that supposedly makes polymer versions (Harmonic Drive Polymer GmbH,

http://www.hd-polymer.com)

but I haven't heard back from them yet.

My question is, does anyone on this forum have any experiences with harmonic drive gearing in a speed-up application? Or with plastic HD gearsets?

Thanks in advance!

 

[MikeHalloran]

I don't think a harmonic drive with that ratio is reversible.

You have to make the planet assembly spin by revolving the wave member, and the pressure angle between the planet rollers and the wave member surface is very unfavorable.




Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

jstewart,

These guys might be able to give you your desired ratio and low backlash. The components could possibly be made of a high performance thermoplastic resin, if you really need a non-metallic device. But most high performance resins (Torlon, Vespel, etc.) are much more expensive than metals.

http://www.ikona.ca/technologies_advantages.shtml

Good luck,
Terry

 

[jstewart]

Thanks for the valuable input!

I've heard back from the harmonic drive people, and it appears that polymer-based harmonic drives exhibit some torque ripple when used in a speed-increasing configuration, and the life isn't very good yet.

It looks like perhaps Ikona might be a better solution; thanks for the link!

FYI, the application is a user-powered exercise machine. These are very cost-competitive, and although the performance isn't very high (500 in-lb at 150 rpm max), it does need to hold up for a while. (100 million cycles, lifetime lubricated.)