Harmonic drive vs Ferguson's Mechanical paradox

[BrianGar]

Is/was the harmonic drive a descendant of Fergusons idea?

Harmonic drive>

http://en.wikipedia.org/wiki/Harmonic_drive

Skip to 6.50 in the video below for what I think is Fergusons doing, but Im not sure if Ferguson ever had an outer gear ring in his plans. But, looking at the drawing below, gears f + h could be the outer rings but just in a different form.

Video,

http://www.youtube.com/watch?v=ttfPo773HEU&feature=related

Original plans/idea

http://chestofbooks.com/crafts/popular-mechanics/Amateur-Work-4/Ferguson-s-Mechanical-Paradox.html

Both the above are 'similar', in that they use 1 or more teeth less for operation.

Could the harmonic drive invention have been a copy of Ferguson's idea?

Another example of Fergusons idea

http://www.youtube.com/watch?v=vWNLDgU6Xl4&feature=related

The reason I ask all this is because Im currently designing a servo powered 4th rotary axis for a cnc machine table and Im getting confused as to where one design starts, and the other stops.

Granted, the harmonic drive due to its design is '0' backlash, but with Fergusons example in the last video posted above, you could fit heavy springs between both gears similar to a scissor gear?

With that In mind, Im thinking torque losses would be similar for both designs, since the harmonic drive 'basket' has to deform while rotated.

Harmonic drives fetch around 3keuro which is why I ask all this.
Perhaps I should just scrap all my thinking, and go with a worm.
That has its downfalls too though.

Interesting stuff for sure,

Thanks in advance for any pointers,

Brian,

 

[MikeHalloran]

Take a look also at doing epicyclic drives with timing belts.



Mike Halloran
Pembroke Pines, FL, USA

 

[BrianGar]

Mike, looked into that.

Do you mean just a 'basic' stepped down pulley drive setup, or is there a way to use the timing belt as a form of ring gear around the planets that Im not seeing?

Thanks,

Brian,

 

[drawoh]

BrianGar,

Harmonic drives are efficient, at least when transmitting maximum power, and worm gears are cheap, and they mostly are self locking at harmonic drive ratios. Which do you want?

The harmonic drives are zero backlash because the wave generators are springy. There are harmonic drive like systems that do have backlash. There is elastic wind-up in a harmonic drive. When I asked them, they told me they could ship their system with a chart showing gear tooth error on that particular one.

On the system I designed, I did not order a gear reducer. I ordered a gear-set, and I integrated this with bearings and a motor to get a very compact drive. Overall, I may even have saved the company money, by eliminating extra bearings, stub shafts and couplings and structure to mount them. Harmonic drive sets are now available integrated with crossed roller bearings.

Again, what do you want to accomplish?

JHG

 

[MikeHalloran]

I was thinking of the sort of drive where the input is an eccentric that causes an external gear or pulley to orbit, and a loose pin or link keeps it from actually rotating. The classical output is an internal gear driven by the orbiting gear. Toothed belts or multirow roller chains allow some variations on that.



Mike Halloran
Pembroke Pines, FL, USA