Suspend those pesky physics laws!

On Fri, 05 Mar 2010 23:40:26 -0600, the infamous Don Foreman scrawled the following:

That brings a thought to mind: Has anyone sued the AGWK "pushers" for pushing bad data on the world, costing it needless billions of dollars? I haven't read of anyone trying to recoup their costs yet, but stay tuned!

-- The blind are not good trailblazers.

-- federal judge Frank Easterbrook

If the problem is too much oil and crap on the wire.... Solve it! Don't raise the drawbridge, lower the river.

Howzabout putting a cleaning station on the unspooling device?

Give the machine the despooled wire after you run it over a series of counter-rotating cleaning rollers (short-nap paint roller covers, cheap in bulk and easily replaceable) that are charged (and flushed) with a small pump and a recycled mild solvent.

Think a wire straightener rig with the rollers staggered over-under, and a gear drive to spin the rollers at maybe 5 to 10 RPM. With a catch-pan under the whole thing.

The last few rollers can have a stripper wiper or a spring loaded rubber brayer roller pressing on them to extract the solvent from the roller cover, then the paint rollers absorb the excess solvent from the wire as it goes over them.

You'll need an oscillator motor and eccentric to move the wire route sideways through the rollers during the day to even out the wear.

(You're welcome. ;-P Run with it and see if you can get anywhere. If it works, I'll give you an address for a little "Care Package".)

-->--

And a right decent income is made by a fair number of folks doing independent testing to develop unbiased data. Unfortunately this usually happens after someone's died or been injured. A good friend worked for Failure Analysis for several years. Much of his work is still covered by NDA, but there's some cases he can talk about. He's got some interesting stories...

Jon

Regardless of approach, this would be a good idea. I've seen very few automated machines feeding any material from coil or roll that doesn't utilize this principle in some fashion or other.

Jon

In my opinion, if this thing is always feeding the same length of wire, a servo is the Rube Goldberg option. 300ms is an eternity to feed and cut a short length of wire for a cam operated device, as long as reasonable care is taken specifying the cam profiles. I've built several wire feed, form and place machines over the past 25 years, including one that operated at 1500 pieces/minute, though that one was a continuous motion device and was servo driven to allow for quick product changes.

But -- not quickly enough. The tape typically ran through a vacuum column one each side to provide a very low inertia, buffer. The The capstan can be pretty quick, but there is a lot of rotational inertia in a full tape reel.

Sometimes, the capstan pinch roller would be engaged/disengaged to start and top the tape, and the servos on the reels would be used to keep the proper amount of tape in the buffers.

Of course, there were densities of up to 5600 BPI, so the tape motion needed to be controlled to about 0.0002" to stop on a bit, (normally, the stops were in an IRG (Inter Record Gap) whose length would have to be determined by the worst case drive. :-)

For the slower ones -- the buffer would be a cats-cradle of tape spooled between the fingers of a "dancing arm".

However, given the likely stiffness of the flat wire being fed, I somehow doubt whether the air column would do anything useful, and even the dancing arms would have to have pretty widely spaced rollers to avoid too sharp a bend.

Yes -- how much precision is needed in the feed again? Were we told, or did I just forget it?

The "dancing arms" -- which with the wire in question, would have to be rather large and at the same time rather low inertia themselves.

I'm sure that he has -- or other "dancing arm" mechanisms.

:-)

Enjoy, DoN.

Lots of good observations and suggestions so far on what appears to be a very interesting project.

Do you really need intermittent feed or is some sort of continuous wire feed with a "flying cutoff" possible, with the length adjustable when the extruded/extended wire trips a proximity or optical switch.

The start/stop inertia of the "flying cutoff" shouldn't be a problem as long as it is consistent and the cutoff trips/cuts at the right time, which could also be controlled by an adjustable switch/trigger.

Would an electric solenoid give faster response than an air cylinder to operate the cut-off? How about a double solenoid to give a push-pull action to avoid problems with spring return. How about a linear motor or push-pull solenoids [no springs] to cycle the flying cutoff back and forth?

Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).

Hmm ... I've thought of another possible approach.

Are you familiar with "Geneva gears"? Input is a constant rotational speed. Output is a precise 1/4 turn (or 1/5th turn or 1/6th turn depending on the particular gear set involved). There should be no overshoot on the output of this. Rotate the input gear with a constant velocity motor, trigger cutoff just a little after the output rotational position locks, and repeat until out of wire.

Here is an example of a Genevia Gear:

Never dealt with them -- and there are other makers of Genevia gears, they were just the first web search hit which looked fairly reasonable.

The Genevia gears even have the advantage that the output rotation accelerates for about half of its revolution, and decelerates for the other half.

Enjoy, DoN.

========= These work great at low speeds, but have high rotational inertia due to lots of moving parts. Max rpm is about 300 or so. With a

Another thought. Have you thought about buying the wires cut to length?

For people that don't know what we are talking about see

Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).

I used the example to keep my post simple, but I really did do the math here. I guessed at 4" dia capstan with a mass of 1 lb, accelerating and decelerating to have peripheral travel of 3" in 0.25 seconds starting and stopping at zero velocity. Peak torque was trivial compared to the capability of even a small servomotor driving direct -- no gears or anything. Torque required was 0.056 Newton-meters, trivial for even a very small coreless servomotor. Accurate design calculation? Of course not, it's a quick sanity check that clearly shows feasibility.

...

Was invented by a machinist at National Cash Register in Dayton, OH. Do not know how it came to be called a Geneva gear. Trivia mode off.

Maybe retain these guys as design consultants?

On 3/7/2010 6:17 PM, Bill McKee wrote: (...)

By convention, one assumes.

--Winston

============

Francis Moon 2005-00-00 Reference :

• Brown : Five Hundred and Seven Mechanical Movements (p. 54,

Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).

Here's a nice animation of a Geneva escapement:

If he'd Google around on "escapements," he'd probably find something suitable.

A 4-step Geneva mechanism has a part that looks like a "Swiss cross", the name must come from that. Of course, there are variants of the mechanism that have a different number of steps per full rev of the output shaft.

Jon

Well, those vacuum-column tape drives had capstans weighing around 10 grams, and accelerating at insane rates, so the gaps in recorded info on the tape could be kept short. To maintain a 0.6" gap, you had 0.3" to start, and 0.3" to stop. The acceleration had to be performed in a sub-millisecond interval. I've got some of the motors used. One is a Yaskawa minertia motor with an ironless rotor and ceramic shaft, the capstan was made of magnesium and fiber composite materials. Typical capstans are about 1.5" diameter.

Jon