For home made engraving machines and some lighter weight machine tools,
bushed round rod ways are practical. Sometimes ball bearings are used
on such ways to reduce the backlash-type of error caused by static and
dynamic coefficients of friction. (Siction)

In assembly and disassembly work, I frequently make use of a stiction
overcoming method, specifically, to keep one axis moving while
postitioning another.

I am thinking now that the bushed round rod ways of a machine tool
could be driven, overcoming stiction.

Let me know if this would be more complicated than ball bearings riding
on the round rod ways.

Remember, bushed ways are self-wiping, while bearings rolling on rods
are very sensitive to "lint" (chips and sward).

Yours,

Doug Goncz
Replikon Research
Seven Corners, VA 22044-0394

You might also try plastic bushings. Something like teflon impregnated
bushings.

Dan

wrote:
For home made engraving machines and some lighter weight machine tools,
bushed round rod ways are practical. Sometimes ball bearings are used
on such ways to reduce the backlash-type of error caused by static and
dynamic coefficients of friction. (Siction)

In assembly and disassembly work, I frequently make use of a stiction
overcoming method, specifically, to keep one axis moving while
postitioning another.

I am thinking now that the bushed round rod ways of a machine tool
could be driven, overcoming stiction.

Let me know if this would be more complicated than ball bearings riding
on the round rod ways.

Remember, bushed ways are self-wiping, while bearings rolling on rods
are very sensitive to "lint" (chips and sward).

Yours,

Doug Goncz
Replikon Research
Seven Corners, VA 22044-0394


You're speaking of turning the rod while a small adjustment is being
made? Should work well.. What about vibrating it? Like when you tap a
piece with a hammer as you're moving it? AC coil set at the end of the rod?

John

wrote:

I am thinking now that the bushed round rod ways of a machine tool
could be driven, overcoming stiction.

This sounds like a good idea!
Be aware that you are probably trading in for a new disadvantage: if the
rod has lengthwise backlash.

Nick
--
WDR Fernsehen:
"Ein Computer arbeitet so lange Befehle ab,
bis keine mehr vorhanden sind."
Muss ich die dann irgendwie nachfüllen?

I like JohnM's suggestion. A piezo crystal mounted at every station
near the end of a rod could provide just the right amount, about a
tenth of a degree, of *rotation* (perpendicular to way travel), to
break stiction once per travel clockwise and counterclockwise. Not
quite as perfect as a rotating rod, but sooo much simpler. I think to
move the rod axially would just introduce random errors into way
travel.

Whadda say, is this one patentable? You could sell premade shafting
with piezo ends, in modular lengths. You would lose the infinite
flexibility in design of having yard long shafting that can be cut to
any length, but gain in the fight for smoothness. A simple controller
could be patched to every rod. A controller with capacity for sixteen
rods would be cover pretty much any machine tool situation. Various
other drives are possible, such as an electromagnetic rod end that
merely needs to be hooked to 110 VAC.

--Doug

On 23 May 2005 02:14:45 -0700, wrote:

I like JohnM's suggestion. A piezo crystal mounted at every station
near the end of a rod could provide just the right amount, about a
tenth of a degree, of *rotation* (perpendicular to way travel), to
break stiction once per travel clockwise and counterclockwise. Not
quite as perfect as a rotating rod, but sooo much simpler. I think to
move the rod axially would just introduce random errors into way
travel.

Whadda say, is this one patentable? You could sell premade shafting
with piezo ends, in modular lengths. You would lose the infinite
flexibility in design of having yard long shafting that can be cut to
any length, but gain in the fight for smoothness. A simple controller
could be patched to every rod. A controller with capacity for sixteen
rods would be cover pretty much any machine tool situation. Various
other drives are possible, such as an electromagnetic rod end that
merely needs to be hooked to 110 VAC.

--Doug

Interesting! When I was using servo hydraulics on an experimental
rig, it was normal to use "dither" to prevent stiction of the spool
valve with its o-rings. I drove it without the usual driver board,
and had to add dither back into the signal. Of course, the servo
spool dither wasn't directly related to the final position of the
cylinder, so you probably couldn't tolerate the magnitude of dither I
used, ~5%. On the other hand, your bushings shouldn't be as sticky as
o-rings.

Pete Keillor

On 23 May 2005 02:14:45 -0700, wrote:

I like JohnM's suggestion. A piezo crystal mounted at every station
near the end of a rod could provide just the right amount, about a
tenth of a degree, of *rotation* (perpendicular to way travel), to

SNIP

A controller with capacity for sixteen
rods would be cover pretty much any machine tool situation. Various
other drives are possible, such as an electromagnetic rod end that
merely needs to be hooked to 110 VAC.

--Doug

Hey Doug,

Geez, I'd have to give that idea a big "Hummmmmm". Maybe some female
operators would like it though?!?

Take care.

Brian Lawson,
Bothwell, Ontario.

On Mon, 23 May 2005 06:58:31 -0400, Pete Keillor
wrote:

On 23 May 2005 02:14:45 -0700, wrote:

I like JohnM's suggestion. A piezo crystal mounted at every station
near the end of a rod could provide just the right amount, about a
tenth of a degree, of *rotation* (perpendicular to way travel), to
break stiction once per travel clockwise and counterclockwise. Not
quite as perfect as a rotating rod, but sooo much simpler. I think to
move the rod axially would just introduce random errors into way
travel.

Whadda say, is this one patentable? You could sell premade shafting
with piezo ends, in modular lengths. You would lose the infinite
flexibility in design of having yard long shafting that can be cut to
any length, but gain in the fight for smoothness. A simple controller
could be patched to every rod. A controller with capacity for sixteen
rods would be cover pretty much any machine tool situation. Various
other drives are possible, such as an electromagnetic rod end that
merely needs to be hooked to 110 VAC.

--Doug

Interesting! When I was using servo hydraulics on an experimental
rig, it was normal to use "dither" to prevent stiction of the spool
valve with its o-rings. I drove it without the usual driver board,
and had to add dither back into the signal. Of course, the servo
spool dither wasn't directly related to the final position of the
cylinder, so you probably couldn't tolerate the magnitude of dither I
used, ~5%. On the other hand, your bushings shouldn't be as sticky as
o-rings.

Pete Keillor
I Dunno if it's still done this way but two of my old CNC lathes have
dither built in to the servo drives. And you can hear it in one
machine when all else is quiet. The repair guy who adjusted the dither
on one machine said it was left over from the hydraulic driven days
and when used in the servo driven machines helped prevent stiction in
the ballscrews.
ERS

A piezo rod end wouldn't have backlash, it'd be of unitary
construction. An electromagnetic rod end might have some. I'll check.
There's a magnetostrictive alloy that could be used.

Can anyone here name any machine tools that use rod ways. I'll start:
Unimat SL.

Doug

wrote:

A piezo rod end wouldn't have backlash, it'd be of unitary
construction.

I understand. But do machines exist that use piezos for that purpose?
And is the travel big enough? And if your way is stiff, the piezo will
have a lot of work. I really don't think that this is an elegant
solution. But you can try to convince me.


Can anyone here name any machine tools that use rod ways. I'll start:
Unimat SL.

Many wabeco's http://http://www.wabeco-remscheid.de/

What? That doesn't count? It's too exotic? Man, the Unimat is from
Austria, so Germany counts! :-P


Greetings,
Nick

--
WDR Fernsehen:
"Ein Computer arbeitet so lange Befehle ab,
bis keine mehr vorhanden sind."
Muss ich die dann irgendwie nachfüllen?

I have an email out to Channel Industries asking if piezos can be
supplied with OD and ID electrodes, poled or patterned to create rotary
motion when energized. It sounds like Nick is thinking of axial motion.
That would certainly be simpler, to have piezos coordinated at both
ends driving axial motion rather than rotary, but it seemed to me that
since the rotary motion would be across the way's motion, that this
would provide more continuous relief from stiction. Ideally, the rod
way would rotate completely continuously, eliminating stiction.

I didn't see any rod ways on the wabeco website. Note doubled http://
in Nick's post.

http://www.wabeco-remscheid.de/

Doug

How about a rod way composed of two lead screws chain driven together,
or two rods as ways with a central lead screw, chain driven so the rods
would break stiction whenever the lead screw turned?

This does seem unnecessarily complicated, with lots of bearings and
chains.

I think I need to come up with something a little less kinematically
redundant.

Doug

On 23 May 2005 02:14:45 -0700, wrote:

I like JohnM's suggestion. A piezo crystal mounted at every station
near the end of a rod could provide just the right amount, about a
tenth of a degree, of *rotation* (perpendicular to way travel), to
break stiction once per travel clockwise and counterclockwise. Not
quite as perfect as a rotating rod, but sooo much simpler. I think to
move the rod axially would just introduce random errors into way
travel.

Whadda say, is this one patentable? You could sell premade shafting
with piezo ends, in modular lengths. You would lose the infinite
flexibility in design of having yard long shafting that can be cut to
any length, but gain in the fight for smoothness. A simple controller
could be patched to every rod. A controller with capacity for sixteen
rods would be cover pretty much any machine tool situation. Various
other drives are possible, such as an electromagnetic rod end that
merely needs to be hooked to 110 VAC.

Interesting idea.

You wouldn't need to lose the flexibility of yard long shafting cut to
length. Just make rotational dither mounts that accept stock
shafting.

Giant magnetrostrictive devices (as Terfenol D) might work better
than piezo here because they exhibit greater strain, hence more motion
per unit length. However, there are more sources for piezoceramic
materials and structures than for giant magnetostrictive materials.

Google searches on "magnetostrictive" and "piezoceramic" will find
lots of material for you.

Piezo and/or magnetostriction aren't the only possible approaches
here. One might also devise a structure that is constrained against
displacement while compliant rotationally, actuated by an alternating
magnetic field. It could be a variable reluctance structure or one
with a permanent magnet. Resonance could be used to magnify rotation.
The SoniCare toothbrush uses these principles: two supermagnets, a
coil actuated by AC, and a resonant beam.

wrote:

It sounds like Nick is thinking of axial motion.

Yes, I did.


That would certainly be simpler, to have piezos coordinated at both
ends driving axial motion rather than rotary, but it seemed to me that
since the rotary motion would be across the way's motion,

Rotary motion would be better in my eyes too.
But still I think that a piezo would not make enough travel to break the
bushing loose. Or the hole thing is vibrating like a ****** (censored).
A continous (that is not back and forth) rotary movement is the best you
can have (at least thats my _oppinion_).

I didn't see any rod ways on the wabeco website. Note doubled http://
in Nick's post.

That's what you get when I think & type & copy & paste. :-)) Sorry.

But here they a
http://www.wabeco-remscheid.de/02_pr...onvdrehen/grun
dausstattung_d2000e.php?rub=2.1.1.1.1
http://www.wabeco-remscheid.de/02_pr...onvdrehen/grun
dausstattung_d2400e.php?rub=2.1.1.2.1
http://www.wabeco-remscheid.de/02_pr...onvdrehen/grun
dausstattung_d3000e.php?rub=2.1.1.3.1

Don't blame me for the long URLs


Greetings,
Nick

--
WDR Fernsehen:
"Ein Computer arbeitet so lange Befehle ab,
bis keine mehr vorhanden sind."
Muss ich die dann irgendwie nachfüllen?

This is interesting, Doug.

No, I'm not going to steal your idea. I'm (mostly) retired!!!

It might be important to learn some about stiction: specifically, how
much relative motion is necessary to overcome it in a given situation
of materials, transverse load, surface finishes and lubrication.
The 0.1 degree you mention seems like a reasonable guess, but I'll bet
it is only a guess. The "answer" may be more one of displacement
rather than degrees; e.g., a 1/2" dia shaft might need more angular
rotation than a 1" dia shaft to achieve the same effect.

You might have to do that by instrumented experimentation. Doing that
might give you proprietary knowledge and a "leg up" toward selecting
the best method of achieving sufficient motion to do the job.

It might be an error to fixate on any given method (piezo,
magnetostriction, etc) this early. Better to understand what needs
doing before selecting a way to do it, even if your instrumentation
uses one of these methods.

Dither has been used for decades in gyroscopes, particularly laser
gyros, to overcome stiction -- or "lockup" in the case of a laser
gyro. Some of them use random noise rather than a fixed frequency.
Random noise (sort of a hiss, like escaping air) might be less
onerous in a shop than a whine or single tone.