ABT Mechanisms For Motions In Microns

How about a lever? with a 1000:1 ratio arms you move the longer arm 1 mm and the shorter arm moves 1 micron!!

John.

ya lever is good one and had thought abt it.. mechanical advantage.. anything else? i needed continuous motion.. thanks anyways..

Look up piezoelectric actuators on Google or Globalspec.

have read about piezoactuators, i wanted to know anything only in mechanical.. something like lever as already mentioned.. isnt there any mechanism like that..

There's something called a differential screw mechanism, but I'm not aware of a linear device utilizing a similar principle. I found a patent document for a "double differential screw" mechanism here.

Looks like an elaborate micrometer tumble mechanism.

It says it is used for the control of precise adjustments to optics and such. I would have thought the focusser mechanisms of large telescopes could utilise something like this as well, several turns for a very small linear offset to move the eyepiece or even the secondary mirror. Interesting stuff.

Hi,

Reduction gear mechanism.

Stud

I had a very cool micrometer that was connected to a box by a wire. When you got the micrometer set, the box would allow you to adjust it to within ±40nm - Yes, I said nanometers!!! It didn't use piezoelectrics - they have trouble with hysteresis.

If I remember correctly, it was made by Newport Optics.

Hi,

there is a ready to buy mechanism that is using a stepper motor input, an excentric ballbearing to convert rotary to linear motion and a flexible mechanism to further reduce the linear travel per motor step.

Resolution is near 10nm so if you really need only 1µm we would have to make a redesign.

This is made for high accuracy optical adjustments.

They make the motor and drive and market the whole, I designed the flex mechanism.

I have to search for the manufacturer an a picture.

Please provide your email adress or tell me how to download a drawing into this text.

RHABE

to put a pic, use insert icon in the toolbar above the text box(the green camera icon) or my email id is ravindramallya@gmail.com

Check www.prior.com

They manufacture microscope stages that are driven with a stepper motor via ball screw to within nanometer accuracy. This is obtained by accurate motors, controler and ballscrew but then measured under a microscope and corrected with error corection values in an eprom.

Pink,

I don't know how harmonic drives have advanced. But there are no adjustment on these systems (at least on Denso 6-axis robots). There is ZERO backlash in this system over it's life. The eliptical spline is pre-stressed against the outer gear. As the the teeth wear the backlash is taken up.

OK, I went too far in saying they would last forever. No mechanical system will last forever. However, I have seen 6-axis robot used and abused and they have never given trouble. The one that did fail was the due to a worn keyway, not the harmonic system. When I removed the drive I could not detect any backlas. These robots have been running trouble free for the last 5 years.

Of course one has to spec. correctly for a specific application. If this is done correctly you will not be replacing "hundreds" every year.

I could go on about how it is not point contact or there fact there is far more then 3 or 4 teeth engaged at any one time, but I must go back to work.

Looking forward to a good arguement.

Regards

Jon

Which one is Pink?

No argument needed as we both are right. Did some looking up and the harmonic drives principle is used in several different configurations. The one you refer to is fixed and the pre adjusted teeth mesh is therefor zero backlash. In my printing machines they were not fixed. you could "undo" the outer rim and turn the race so that it turned the grip point of the flexi inner ring which in turn rotates one of the inner collars. This was done so that you could offset the driven cylinder from the driving shaft which gives you the final adjustment needed to position the print in the up and down direction.

Same device but mechanically slightly different. Due to the adjustments ours did wear.

Still a very interesting mechanical device and never failed to amaze other engineers with explanation of how it realy works. When asked they would always think there has to be loads of tiny gears inside to get the ratio of the drive.

Case491,

I have also tried to explain this system to others. No one has ever fully grasps the concept until I show the amination link in my 1st reply.

You got to admire the guy that invented it.

See you on the dark side of the moon.

Jon

http://www.harmonicdrive.net/reference/operatingprinciples/

A harmonic drive is a relatively inexpensive, highly precise reduction gearbox with zero backlash. It give a 100:1 reduction. It only contains 3 moving parts, and will last forever (within reason).

They are used in mutiple axis robots. I've only ever seen one of the give trouble and that was from miss-use.

If your input is in meters 2 will have to be used in series. I don't know if this is possible, but if it is, it is the cheapest solution and very realible

Jon

I worked with harmonic drives extensively as they were used on printing machines to register the colours and give them adjust-ability both stationary and on the fly.

These harmonic drives are not zero backlash when they are not tightened up and when tightened up, they will not last forever due to the ever action of teeth crushing and screw wear and tear.

These 3 parts you mentioned is correct but the principle they work on is the offset of one tooth between the 2 inner collars. The outer ring will have a few more teeth on its inner circumference and by squeezing it into an oval outer race, you create 2 opposing points of contact between the inner collars and the inner sleeve. The sleeve will only have 3 or 4 teeth meshed with the inner collars on 2 opposing points. This means that if it is not tightened up, the load capacity is drastically reduced and you will wear those teeth a lot more then when you would tighten it up.

Tightening is done with the outer race and simply by clamping it down on one end. This creates forces on the teeth that are out of normal spec which also causes wear.

To state it bluntly, you cannot expect this part to perform either way or the other without taking the complete mode of usage into account. We used to replace harmonic drives by the hundreds globally. Each machine would be different depending on maintenance procedures in the factory but generally speaking the shortest life expectancy was 1 year and the maximum was 5 years with the average roughly between the 1.5 and the 2.5 years.

thank you very much for all the important info.. i am very happy as u can see..

thanks for the link.. i'll go thru it..

Some 15 years back I ran ito a mechanism which was a sort of 3-D pantograph where large movements of the input link would be accurately mimicked at a much smaller scale by the output end. This was for manupulating objects at sub-millimeter level if not at micron level. I think it was made by Singer. I don't know if the same mechanism can be re-designed to handle micron level adjustments.

ohh is it? 15 yrs back..long time.. i think technology wud have advanced by now.. and am sure some new and efficient mechanisms might b available.. anyways i'll do a google on it and c if i can find anythiing..

Be sure to let us know how many angels can fit on the head of a pin!