Suspend those pesky physics laws!
Buerste
I have an air cylinder, 1.5" x 4" stroke, that pushes a crank on a shaft to
rotate the shaft about 90 deg. On the shaft is a gear with a one-way
clutch. The 4" x 1/2" gear turns about 3" at the perimeter per stroke of
the cylinder. By moving the link to the air cylinder up or down on the
crank the gear will rotate more or less per stroke. A second gear is meshed
into the first gear with pressure from another air cylinder. Wire is fed
between the gears in a grove cut in the face of each gear. The idea is to
feed wire 3" per stroke.
Is works perfectly and fast! By varying the pressure in the cylinder that
presses the gears together, the wire is gripped very well at 60 lbs air
pressure and will slip through the gears easily at no pressure.
The only problem I have is that the gears over-run and feed too much wire.
I've considered lightening the gears by drilling a bunch of holes. Also, a
drag brake on one or both gears with screws pressing brass pucks against it.
Another idea is an air limit switch that is struck at the end of the stroke
by the crank. This switch would unload the pressure on the clamping
cylinder and let the wire slip between the gears when they over-run.
Would the air limit switch work fast enough to unclamp the wire in time?
Would I be better off with an electric switch and valve? I might have to
lighten the gears, brake them and switch off the air clamp The feed has to
take place in <300ms.
Richard J Kinch
> Would I be better off with an electric switch and valve?
The flaw of your design is that you do not control acceleration and
deceleration, which not only is brutal, but prohibits precision control
such as you describe. Curing an excess deceleration problem by braking and
adding more deceleration is not a sound approach. You are controlling
position mechanically, and perhaps the second derivative of velocity via
air pressure, but not the second derivative. You are adding excess energy
that is mechanical noise showing up as precision error.
Figure out a way to decelerate evenly at the end of travel, so your
mechanism comes to a controlled, smooth stop. You will get better
precision, you will use less energy, and your mechanism will wear slower
and last longer.
Buerste
"Richard J Kinch" <ki...@truetex.com> wrote in message
news:Xns9D319698441...@216.196.97.131...
The obvious method would be to use a servo and program in the ramps. Too
expensive at this point, maybe in the future.
I have considered a hydraulic damper near the end of stroke to bleed off the
energy and not abruptly shock the system. But you see why if I unclamp the
wire, because it has so little mass it's momentum is negligible. The trick
I see is unclamping it at the right time so it coasts to a stop at the right
place against the steel block at the far end.
Tim Wescott
roller and by the steel block? Ooh, bad you.
If the wire's momentum is negligible, can you adjust the tension on the
clamping gears so that as soon as it hits the block it stops? Or do the
gears fly back a bit after they stop at full extent?
I think a shock absorber on the cylinder (not 'damper', not for this, in
the US at least -- believe me, I've been living the terminology for the
last few months on That Damned Gate Project) would work quite well,
particularly if you could arrange for it to have a bit of a progressive
action. You can get little screw-in shock absorbers that are spring
loaded, damp when something lands on them, then return to 'out' when you
retract whatever it is that is pushing on the thing.
I'll bet you could select one of those that would work quite well,
particularly if you put a spring on the end of it so that deceleration
force is progressive rather than getting applied suddenly.
Alternately you could valve the cylinder so that as it gets close to
full extent the feed gets choked off -- I couldn't tell without doing
the math, but it seems like there'd be a 'right' combination of cut off
position and residual valve opening that would start bleeding off the
speed while still providing enough flow to complete the stroke at an
appropriately slow rate. In theory this would act exactly like the
shock absorber I'm suggesting, just using the cylinder as the damper and
the air as the working fluid.
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Carl Ijames
cylinders?
-----
Regards,
Carl Ijames
"Richard J Kinch" <ki...@truetex.com> wrote in message
news:Xns9D319698441...@216.196.97.131...
Karl Townsend
If I understand your application correctly, this just screams for a servo
motor.
I used to work with Parker Compumotor products. They have unbelievably top
notch customer service. I'd at least give them a call. Programming one of
these compumotor units is very simple.
Karl
technomaNge
> Damn inertia!
>
> I have an air cylinder, 1.5" x 4" stroke, that pushes a crank on a shaft to
> rotate the shaft about 90 deg. On the shaft is a gear with a one-way
> clutch. The 4" x 1/2" gear turns about 3" at the perimeter per stroke of
> the cylinder. By moving the link to the air cylinder up or down on the
> crank the gear will rotate more or less per stroke. A second gear is meshed
> into the first gear with pressure from another air cylinder. Wire is fed
> between the gears in a grove cut in the face of each gear. The idea is to
> feed wire 3" per stroke.
If these are 3" cuts, separate the operations.
Cut, pieces fall into sorting/stacking bin, a different machine feeds
the cuts to your existing machine.
technomaNge
--
Due to anticipated high turnout in 2010's election,
the Electorial College has scheduled:
Nov. 1, 2010 All Independents vote.
Nov. 2, 2010 All Republicans vote.
Nov. 3, 2010 All Democrats vote.
Denis G.
Bimba makes air cylinders with adjustable internal air cushions.
Maybe if you used one of those to cushion the end of the 1.5 x 4"
cylinder's stroke, it might be enough to slow the wire feed gears
enough (with the one-way clutch still engaged) so they don't
freewheel.
http://www.bimba.com/Products/OriginalLineCylinders/AirCylinderswithAdjustableCushions/
The largest diameter cylinder in the above link is 3", but you might
ask a rep if he can supply one similar to the air cylinder you're
using.
Don Foreman
wrote:
I'd say you need to do better at defining your objective without
trying to preserve ego invested in design thus far. The only
objective I see stated here is to move wire 3" in <300 milliseconds. I
suspect that there are further unstated constraints or strong wants.
Buerste
"Carl Ijames" <x...@yyy.zzz> wrote in message
news:hmpio...@news6.newsguy.com...
> Can you just slow it down a little by restricting the airflow into the
> cylinders?
>
> -----
> Regards,
> Carl Ijames
Both cylinders have speed controls on both ends. On the bench, at slow
speed, there is no over-run. But I have a 300ms window to feed.
Buerste
"Karl Townsend" <karltown...@embarqmail.com> wrote in message
news:4b9055ff$0$5835$892e...@auth.newsreader.octanews.com...
I figure about $2500-$3,000. The guys at Carlson Tool (they make brush
machines) do a lot of feeds with servos and mechanical methods and they have
servo set-ups that could work. You'd be surprized how beefy it has to be.
My original design uses a servo, but why stop there...the "X" and "Y" axis
on the table might as well be servo driven too. That works great for brush
machines that change set-ups often but this machine never will, so cam
actuation works just fine and is oh so simple.
I don't mind spending the money but I'll explore the mechanical first.
Buerste
"technomaNge" <pir...@microsoft.com> wrote in message
news:hmpn2s$1n3$1...@news.eternal-september.org...
> Buerste wrote:
>> Damn inertia!
>>
>> I have an air cylinder, 1.5" x 4" stroke, that pushes a crank on a shaft
>> to rotate the shaft about 90 deg. On the shaft is a gear with a one-way
>> clutch. The 4" x 1/2" gear turns about 3" at the perimeter per stroke of
>> the cylinder. By moving the link to the air cylinder up or down on the
>> crank the gear will rotate more or less per stroke. A second gear is
>> meshed into the first gear with pressure from another air cylinder. Wire
>> is fed between the gears in a grove cut in the face of each gear. The
>> idea is to feed wire 3" per stroke.
>
>
>
> If these are 3" cuts, separate the operations.
> Cut, pieces fall into sorting/stacking bin, a different machine feeds
> the cuts to your existing machine.
>
>
> technomaNge
> --
That's how it's done with round wire. With this flat wire, you can never
lose control of it.
Buerste
"Don Foreman" <dfor...@NOSPAMgoldengate.net> wrote in message
news:d481p59cpm7vtmju8...@4ax.com...
Hmmm, the wire needs to be in place and in control to be cut in the 300ms
window, that's all. This is the third wire feeder design in ten years.
We've had to use different wire manufacturers over the years as some plants
have closed and the qualities of the wire change...this or that feed doesn't
work on this or that wire too well...etc. This feeder is trying to address
the wire that has too much oil, too much scale, lead drag, ect. The wire
manufacturer can't fine-tune their quality any better and they are the only
domestic supplier. We also use a Taiwanese supplier but their QC and
lead-time is worse. Those are the only suppliers in the entire world! And,
there are only 4 customers in the world and we are by far the largest user.
Karl Townsend
The stops and starts are killing ya. So, don't stop. Put your cutoff
mechanism and clamp on a turntable. Spindle diameter determines length.
You'll probably need multiple stations to get the layout to work, say do
four stations and use a twelve inch circumference spindle. You can use cams,
air or electric solenoids to move devices.
I used to work for a company that made a million rolls of adhesive tape a
day. We had a few of this idea machine for cut to length tape. Of course,
the first machine we made this way was a total POS. We rebuilt it and it was
only crappy. Then we built one from scratch and it would run 24 hours
straight without a stop. Quite a few more operations than you have. The
turntable was eight feet in diameter.
Karl
Larry Jaques
<bue...@buerste.com> scrawled the following:
>Damn inertia!
>
>I have an air cylinder, 1.5" x 4" stroke, that pushes a crank on a shaft to
>rotate the shaft about 90 deg. On the shaft is a gear with a one-way
>clutch. The 4" x 1/2" gear turns about 3" at the perimeter per stroke of
>the cylinder. By moving the link to the air cylinder up or down on the
>crank the gear will rotate more or less per stroke. A second gear is meshed
>into the first gear with pressure from another air cylinder. Wire is fed
>between the gears in a grove cut in the face of each gear. The idea is to
>feed wire 3" per stroke.
What kind? Mangrove? Orange grove?
>Is works perfectly and fast! By varying the pressure in the cylinder that
>presses the gears together, the wire is gripped very well at 60 lbs air
>pressure and will slip through the gears easily at no pressure.
>
>The only problem I have is that the gears over-run and feed too much wire.
That doesn't sound quite like "perfectly" to me. <g>
>I've considered lightening the gears by drilling a bunch of holes. Also, a
>drag brake on one or both gears with screws pressing brass pucks against it.
>Another idea is an air limit switch that is struck at the end of the stroke
>by the crank. This switch would unload the pressure on the clamping
>cylinder and let the wire slip between the gears when they over-run.
>
>Would the air limit switch work fast enough to unclamp the wire in time?
>Would I be better off with an electric switch and valve? I might have to
>lighten the gears, brake them and switch off the air clamp The feed has to
>take place in <300ms.
Why not feed 'em with stepper motors turning the gears, Tawm? That
would be much more precise than having to maintain exact feed tension
and maintain split-second air timing unless you're actually ratcheting
the gears. That design would make for a high-maintenance situ, tho.
--
An author spends months writing a book, and maybe puts his
heart's blood into it, and then it lies about unread till
the reader has nothing else in the world to do.
-- W. Somerset Maugham, The Razor's Edge, 1943
Jon Anderson
> That's how it's done with round wire. With this flat wire, you can never
> lose control of it.
Are you sure about that? I've seen some pretty clever mechanical means
for feeding and orienting small parts. I'm guessing there's something
proprietary about the process, but if you could reveal a bit more
detail, that might be helpful.
One thought I had would be to feed through rollers with one way clutches
to prevent the wire from slipping backward. Then feed through a set of
jaws that work like those on strapping tape tension tools. These jaws
would be on a linear slide, to be reciprocated by a crank. The mechanics
of the crank will provide deceleration at both ends of travel. Stroke
length easily adjustable in the same fashion used by shapers.
Either an electromagnetic clutch or a servo motor to drive the crank, if
there is need for dwell between each feed cycle.
Jon
pyotr filipivich
Thu, 4 Mar 2010 14:31:33 -0500 did write/type or cause to appear in
rec.crafts.metalworking the following:
>
>Is works perfectly and fast! By varying the pressure in the cylinder that
>presses the gears together, the wire is gripped very well at 60 lbs air
>pressure and will slip through the gears easily at no pressure.
>
>The only problem I have is that the gears over-run and feed too much wire.
>I've considered lightening the gears by drilling a bunch of holes. Also, a
>drag brake on one or both gears with screws pressing brass pucks against it.
>Another idea is an air limit switch that is struck at the end of the stroke
>by the crank. This switch would unload the pressure on the clamping
>cylinder and let the wire slip between the gears when they over-run.
Sounds like a "delay" between when you say "stop" and it does
actually stop. Reminds me of a story about teaching a bunch of
farmers to use small boats. They were used to tractors, which only
turn when the steering wheel turned. Turn the wheel hard over, make a
90 degree turn, then straighten the wheel, "plow on". Small boats,
otoh, keep turning. One needs to stop 'turning' before completing the
turn, so that the boat is going "straight" when it gets to the new
heading.
So "re-calibrate". That is, if X amount of time produces Y amount
of wire, shorten X. Seems to me the air limit switch is an idea for
doing just that. Cut off the air so that the "overrun" produces the
last amount of travel needed to get the right amount of wire. That
"over travel" is not a bug, it is a feature.
pyotr
-
pyotr filipivich
We will drink no whiskey before its nine.
It's eight fifty eight. Close enough!
Tim Wescott
This is kinda sorta the absolutely worst sort of application for
steppers. High acceleration = high torque; steppers don't produce much
torque for their size or power input compared to DC motors, and when you
ask for more torque than they can deliver they lose their place
completely. So pushing a stepper for more torque leads to reliability
issues -- you can sacrifice great chunks of an otherwise enjoyable
engineering career to trying to make an undersized stepper reliably
accelerate and decelerate.
Besides, by the time you get a stepper and a stepper controller designed
in, you could well have designed in a brushless motor and a servo
controller -- and with careful design, the only thing that happens if
your brushless motor lacks oomph is that things slow down a bit.
There are applications for which you'd be crazy to use anything other
than a stepper, by the way -- if you've got space and power to burn, you
only need moderate precision for the speed, and tuning a servo motor may
be a questionable exercise, steppers are superlative little gems. But
"go from point A to point B damn fast and stop" is not a strength of a
stepper, in my experience.
pyotr filipivich
or about Fri, 05 Mar 2010 06:17:53 -0800 did write/type or cause to
appear in rec.crafts.metalworking the following:
>
>
>>presses the gears together, the wire is gripped very well at 60 lbs air
>>pressure and will slip through the gears easily at no pressure.
>>
>>The only problem I have is that the gears over-run and feed too much wire.
>
>That doesn't sound quite like "perfectly" to me. <g>
Oh it works perfectly, just as designed and built! But the
results aren't what he wanted.
I hate it when machines do what I tell them, not what I want. B-)
Gunner Asch
wrote:
Ball screws work very good at this if combined with a PLC and sensor
Gunner
Whenever a Liberal utters the term "Common Sense approach"....grab your
wallet, your ass, and your guns because the sombitch is about to do
something damned nasty to all three of them.
Tim Wescott
> On Thu, 04 Mar 2010 13:48:15 -0600, Richard J Kinch <ki...@truetex.com>
> wrote:
>
>> Buerste writes:
>>
>>> Would I be better off with an electric switch and valve?
>> The flaw of your design is that you do not control acceleration and
>> deceleration, which not only is brutal, but prohibits precision control
>> such as you describe. Curing an excess deceleration problem by braking and
>> adding more deceleration is not a sound approach. You are controlling
>> position mechanically, and perhaps the second derivative of velocity via
>> air pressure, but not the second derivative. You are adding excess energy
>> that is mechanical noise showing up as precision error.
>>
>> Figure out a way to decelerate evenly at the end of travel, so your
>> mechanism comes to a controlled, smooth stop. You will get better
>> precision, you will use less energy, and your mechanism will wear slower
>> and last longer.
>
> Ball screws work very good at this if combined with a PLC and sensor
>
But how to meet the 300ms travel time with just a PLC for control?
Buerste
"Jon Anderson" <jande...@comcast.net> wrote in message
news:9W9kn.23895$Vq1....@en-nntp-03.dc1.easynews.com...
That basically describes feeder #2 but it's driven by air not a motor. I'll
post pix of some of the feeders we still have along with the new one.
Buerste
I can visualize that!
Buerste
"pyotr filipivich" <ph...@mindspring.com> wrote in message
news:lng2p5t4mpaelopmu...@4ax.com...
My sediments exactly!
Buerste
Yep! But I hate these "Kentucky Windage" things!
Buerste
"Larry Jaques" <lja...@diversify.invalid> wrote in message
news:5642p5d1eult3s9d7...@4ax.com...
You're always so MEAN to me!
Steppers don't have the speed or oomph and I'm a "MECHANICAL" engineer! Get
it...mechanical??? Anybody can just stick in electronics but it takes a
mechanical guy to do a "Rube Goldberg".
chaniarts
could you stop it with electromagnets?
Jon Anderson
> That basically describes feeder #2 but it's driven by air not a motor. I'll
> post pix of some of the feeders we still have along with the new one.
Would love to see a picture of #2. If I get what you're saying above,
you were using an air cylinder to advance the one-way jaw in a linear
fashion? If so... I'm talking about a crankshaft and connecting rod type
setup. Though the crank rotates at a constant velocity, the linear
output slows to a smooth stop at each end of travel.
But a picture's worth a thousand words... I'll watch for your posting of
them.
Jon
Tim Wescott
You wouldn't say that if you read the source code for a few products
with embedded processors. Embedded software is the ultimate Rube
Goldberg artifact, it's just well hidden.
You shred mechanical drawings so your competitors can't copy your product.
You shred electrical drawings so your competitors can't get an idea of
how you think.
You shred source code so your competitors won't laugh at you.
Tim Wescott
They have a nasty tendency to change with time and temperature. You
want the machine to serve you, not the other way around.
Buerste
"chaniarts" <charlie...@nospam.stratus.com> wrote in message
news:hmrmd5$b08$1...@news.eternal-september.org...
Sure, a magnetic particle brake is being considered as well as an air
caliper brake.
Buerste
"Tim Wescott" <t...@seemywebsite.now> wrote in message
news:rKGdnSF76K4Z6AzW...@web-ster.com...
My good friends at Carlson Tool, they make brush machines, does machine
shows in China. They change the labels on the servo gear boxes so that the
gear ratios are WAY off.
Buerste
"Tim Wescott" <t...@seemywebsite.now> wrote in message
It has to do with the planet Mercury...
chaniarts
it's the phase of the moon
axolotl
you could well have designed in a brushless motor
Tom doesn't do brushless.
Kevin Gallimore
Larry Jaques
<bue...@buerste.com> scrawled the following:
>
Sedimentary, my dear Watson.
Larry Jaques
<bue...@buerste.com> scrawled the following:
>
Yeah, the exact opposite effect of shooting machine gun rounds between
the prop blades on a WWI fighter. But when the timing's off, it goes
through a helluva lot of material in a short period.
Charles U Farley
Larry Jaques
<bue...@buerste.com> scrawled the following:
I'll take that as "orange grove", then. Thanks.
>Steppers don't have the speed or oomph
Really? What kind of forces are we talkin' here? Is your leetle thang
physically tugging on the gigantic 2T spool of wire?
>and I'm a "MECHANICAL" engineer! Get
>it...mechanical??? Anybody can just stick in electronics but it takes a
>mechanical guy to do a "Rube Goldberg".
If I'd gone to college, I'd have taken both courses and come out an
EME who could leap over tall buildings in a single electromechanical
bound!
Well, since you're too tightarsed to go with servos, Rube away, sir!
Larry Jaques
<bue...@buerste.com> scrawled the following:
>
>"chaniarts" <charlie...@nospam.stratus.com> wrote in message
>news:hmrmd5$b08$1...@news.eternal-september.org...
>> could you stop it with electromagnets?
>
>Sure, a magnetic particle brake is being considered as well as an air
>caliper brake.
Then what do you do with the magnetized bits of wire? 8-/
Don Foreman
wrote:
>
>You wouldn't say that if you read the source code for a few products
>with embedded processors. Embedded software is the ultimate Rube
>Goldberg artifact, it's just well hidden.
>
>You shred mechanical drawings so your competitors can't copy your product.
>
>You shred electrical drawings so your competitors can't get an idea of
>how you think.
>
>You shred source code so your competitors won't laugh at you.
A corollalary is that you conceal test data to try to avert predation
by lawyers and politicans.
Don Foreman
wrote:
>Damn inertia!
>
>I have an air cylinder, 1.5" x 4" stroke, that pushes a crank on a shaft to
>rotate the shaft about 90 deg. On the shaft is a gear with a one-way
>clutch. The 4" x 1/2" gear turns about 3" at the perimeter per stroke of
>the cylinder. By moving the link to the air cylinder up or down on the
>crank the gear will rotate more or less per stroke. A second gear is meshed
>into the first gear with pressure from another air cylinder. Wire is fed
>between the gears in a grove cut in the face of each gear. The idea is to
>feed wire 3" per stroke.
>
>Is works perfectly and fast! By varying the pressure in the cylinder that
>presses the gears together, the wire is gripped very well at 60 lbs air
>pressure and will slip through the gears easily at no pressure.
>
>The only problem I have is that the gears over-run and feed too much wire.
>I've considered lightening the gears by drilling a bunch of holes. Also, a
>drag brake on one or both gears with screws pressing brass pucks against it.
>Another idea is an air limit switch that is struck at the end of the stroke
>by the crank. This switch would unload the pressure on the clamping
>cylinder and let the wire slip between the gears when they over-run.
>
>Would the air limit switch work fast enough to unclamp the wire in time?
>Would I be better off with an electric switch and valve? I might have to
>lighten the gears, brake them and switch off the air clamp The feed has to
>take place in <300ms.
I would consider a low-inertia servo motor driving wire-drive
capstans. Recall the action on reel-to-reel tape digital data storage
years ago? Those fairly large reels started and stopped very quickly.
In your case, the diameter and mass of the drive capstans (gears if
you like) should be somewhat matched to the servomotors or vicey
versey. A servomotor is essentially a current-to-torque transducer
but you must factor in its own moment of inertia into torque
calculations. That torque can be braking torque as well as
accelerating torque.
If the wire comes from a large spool with significant moment of
inertia, then a secondary mechanism would be in order that feeds a
"wire buffer" like on a coil winding machine so that all the feed
mechanism need do is accelerate and decelerate a few feet of wire and
overcome the mild resistance of the springs or weights in the buffer.
The spool would have its own servo drive that would run at fairly
constant speed with the buffer handling the reciprocating difference
in slack. If you haven't seen a coil winding machine, visit a company
that makes transformers.
This is all moot if you're determined to Rube it with a completely
mechanical solution.
Larry Jaques
<dfor...@NOSPAMgoldengate.net> 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
Bruce L. Bergman
wrote:
>Hmmm, the wire needs to be in place and in control to be cut in the 300ms
>window, that's all. This is the third wire feeder design in ten years.
>We've had to use different wire manufacturers over the years as some plants
>have closed and the qualities of the wire change...this or that feed doesn't
>work on this or that wire too well...etc. This feeder is trying to address
>the wire that has too much oil, too much scale, lead drag, ect. The wire
>manufacturer can't fine-tune their quality any better and they are the only
>domestic supplier. We also use a Taiwanese supplier but their QC and
>lead-time is worse. Those are the only suppliers in the entire world! And,
>there are only 4 customers in the world and we are by far the largest user.
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".)
--<< Bruce >>--
Jon Anderson
> A corollalary is that you conceal test data to try to avert predation
> by lawyers and politicans.
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
Jon Anderson
> If the wire comes from a large spool with significant moment of
> inertia, then a secondary mechanism would be in order that feeds a
> "wire buffer" like on a coil winding machine so that all the feed
> mechanism need do is accelerate and decelerate a few feet of wire and
> overcome the mild resistance of the springs or weights in the buffer.
> The spool would have its own servo drive that would run at fairly
> constant speed with the buffer handling the reciprocating difference
> in slack. If you haven't seen a coil winding machine, visit a company
> that makes transformers.
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
Ned Simmons
wrote:
>
>Steppers don't have the speed or oomph and I'm a "MECHANICAL" engineer! Get
>it...mechanical??? Anybody can just stick in electronics but it takes a
>mechanical guy to do a "Rube Goldberg".
>
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.
--
Ned Simmons
DoN. Nichols
> On Thu, 4 Mar 2010 14:31:33 -0500, "Buerste" <bue...@buerste.com>
> wrote:
>
>>Damn inertia!
[ ... ]
> I would consider a low-inertia servo motor driving wire-drive
> capstans. Recall the action on reel-to-reel tape digital data storage
> years ago? Those fairly large reels started and stopped very quickly.
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.
> In your case, the diameter and mass of the drive capstans (gears if
> you like) should be somewhat matched to the servomotors or vicey
> versey. A servomotor is essentially a current-to-torque transducer
> but you must factor in its own moment of inertia into torque
> calculations. That torque can be braking torque as well as
> accelerating torque.
Yes -- how much precision is needed in the feed again? Were we
told, or did I just forget it?
> If the wire comes from a large spool with significant moment of
> inertia, then a secondary mechanism would be in order that feeds a
> "wire buffer" like on a coil winding machine so that all the feed
> mechanism need do is accelerate and decelerate a few feet of wire and
> overcome the mild resistance of the springs or weights in the buffer.
The "dancing arms" -- which with the wire in question, would
have to be rather large and at the same time rather low inertia
themselves.
> The spool would have its own servo drive that would run at fairly
> constant speed with the buffer handling the reciprocating difference
> in slack. If you haven't seen a coil winding machine, visit a company
> that makes transformers.
I'm sure that he has -- or other "dancing arm" mechanisms.
> This is all moot if you're determined to Rube it with a completely
> mechanical solution.
:-)
Enjoy,
DoN.
--
Email: <dnic...@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
F. George McDuffee
>The only problem I have is that the gears over-run and feed too much wire.
>I've considered lightening the gears by drilling a bunch of holes.
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).
DoN. Nichols
> On Thu, 4 Mar 2010 14:31:33 -0500, "Buerste"
><bue...@buerste.com> wrote:
><snip>
>>The only problem I have is that the gears over-run and feed too much wire.
>>I've considered lightening the gears by drilling a bunch of holes.
><snip>
> 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.
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:
<http://www.tangendrives.com/>
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.
F. George McDuffee
wrote:
<snip>
> 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:
>
> <http://www.tangendrives.com/>
>
> 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.
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
4 slot cross this would be about 1200 cuts per minute max.
Another thought. Have you thought about buying the wires cut to
length?
For people that don't know what we are talking about see
http://en.wikipedia.org/wiki/Geneva_drive
Off the shelf Geneva units look like a spicy meatball...
http://www.thomasnet.com/products/universal-drives-24411308-1.html
http://www.wmberg.com/catalog/productsearch.aspx?url=http://wmberg.smartcats.com/sc_app/default.asp
http://www.thomasnet.com/heading.html?cov=NA&what=%22geneva+drive%22+suppliers&heading=24411308&searchpos=19&cid=10056509
also see
http://www.accrainc.com/ctl.html
Don Foreman
wrote:
>On 2010-03-06, Don Foreman <dfor...@NOSPAMgoldengate.net> wrote:
>> On Thu, 4 Mar 2010 14:31:33 -0500, "Buerste" <bue...@buerste.com>
>> wrote:
>>
>>>Damn inertia!
>
> [ ... ]
>
>> I would consider a low-inertia servo motor driving wire-drive
>> capstans. Recall the action on reel-to-reel tape digital data storage
>> years ago? Those fairly large reels started and stopped very quickly.
>
> 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.
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.
Bob Engelhardt
> These [Geneva gears] work great at low speeds, ... Max rpm is about 300 or so. With a
> 4 slot cross this would be about 1200 cuts per minute max.
1200/min = 20/sec, well beyond Buerste's 300ms speed. Bob
Bill McKee
"DoN. Nichols" <dnic...@d-and-d.com> wrote in message
news:slrnhp6ebh....@Katana.d-and-d.com...
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.
Don Foreman
Winston
(...)
> Do not know how it came to be called a Geneva gear.
By convention, one assumes.
--Winston
F. George McDuffee
============
http://kmoddl.library.cornell.edu/model.php?m=481
<snip>
Geneva movement is so called because of its use in Geneva watches
as a stop wind.
<snip>
[Editor�s Note: This is a classic Geneva mechanism used in Swiss
watches in the late 19th century. It is also of a general class
of intermittent ratchet kinematic devices that change continuous
rotary motion into digital motion. Such devices are often used in
counting mechanisms. Similar Models in the Reuleaux-Voigt catalog
include N-8 and N-9. FCM]
Francis Moon 2005-00-00
Reference :
* Brown : Five Hundred and Seven Mechanical Movements (p. 54,
55, 1871)
* Reuleaux, Kennedy : Kinematics of Machinery (p. 564, 1876)
* Clark, Downward : Mechanical Models (1930)
<snip>
Ed Huntress
"F. George McDuffee" <gmcd...@mcduffee-associates.us> wrote in message
news:9ahap5p6d98m7cjt8...@4ax.com...
Here's a nice animation of a Geneva escapement:
http://www.brockeng.com/mechanism/Geneva.htm
It sounds like Tawwwm needs some kind of escapement for this job. There are
many types, including the Geneva mechanism, but I've never encountered one
that's adjustable. If you want to start and stop some fixed amount of
rotation, however, there are many of them.
If he'd Google around on "escapements," he'd probably find something
suitable.
--
Ed Huntress
Jon Elson
> On 3/7/2010 6:17 PM, Bill McKee wrote:
> (...)
>
>> Do not know how it came to be called a Geneva gear.
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
Jon Elson
> 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.
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
Jon Elson
I think they use 4 steps/rev, so the output shaft is moving at 360
revs/minute. The mechanism is advancing 1440 times/minute.
They do use some VERY light parts in these, or they'd hammer themselves
to pieces.
Jon
Paul Hovnanian P.E.
>
> "Richard J Kinch" <ki...@truetex.com> wrote in message
> news:Xns9D319698441...@216.196.97.131...
> > Buerste writes:
> >
> >> Would I be better off with an electric switch and valve?
> >
> > deceleration, which not only is brutal, but prohibits precision control
> > such as you describe. Curing an excess deceleration problem by braking
> > and
> > adding more deceleration is not a sound approach. You are controlling
> > position mechanically, and perhaps the second derivative of velocity via
> > air pressure, but not the second derivative. You are adding excess energy
> > that is mechanical noise showing up as precision error.
> >
> > Figure out a way to decelerate evenly at the end of travel, so your
> > mechanism comes to a controlled, smooth stop. You will get better
> > precision, you will use less energy, and your mechanism will wear slower
> > and last longer.
>
> The obvious method would be to use a servo and program in the ramps. Too
> expensive at this point, maybe in the future.
>
> I have considered a hydraulic damper near the end of stroke to bleed off the
> energy and not abruptly shock the system. But you see why if I unclamp the
> wire, because it has so little mass it's momentum is negligible. The trick
> I see is unclamping it at the right time so it coasts to a stop at the right
> place against the steel block at the far end.
Control the clamping with a spring and a cam so its based on the
position of the feed. It sounds like you are having problems controlling
the air driven clamping scheme timing.
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
A physicist is an atom's way of knowing about atoms.
-- George Wald
Paul Hovnanian P.E.
>
[snip]
> If the wire comes from a large spool with significant moment of
> inertia, then a secondary mechanism would be in order that feeds a
> "wire buffer" like on a coil winding machine so that all the feed
> mechanism need do is accelerate and decelerate a few feet of wire and
> overcome the mild resistance of the springs or weights in the buffer.
> The spool would have its own servo drive that would run at fairly
> constant speed with the buffer handling the reciprocating difference
> in slack. If you haven't seen a coil winding machine, visit a company
> that makes transformers.
Transformers are all made in China now. The coil winding machines you
refer to are 10 year olds.
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
"Arguing with anonymous strangers on the Internet is a sucker's game
because they almost always turn out to be, or to be indistinguishable
from
self-righteous sixteen-year-olds possessing infinite amounts of free
time."
- Neil Stephenson, _Cryptonomicon_
Don Foreman
<Pa...@Hovnanian.com> wrote:
>Don Foreman wrote:
>>
>[snip]
>
>> If the wire comes from a large spool with significant moment of
>> inertia, then a secondary mechanism would be in order that feeds a
>> "wire buffer" like on a coil winding machine so that all the feed
>> mechanism need do is accelerate and decelerate a few feet of wire and
>> overcome the mild resistance of the springs or weights in the buffer.
>> The spool would have its own servo drive that would run at fairly
>> constant speed with the buffer handling the reciprocating difference
>> in slack. If you haven't seen a coil winding machine, visit a company
>> that makes transformers.
>
>Transformers are all made in China now. The coil winding machines you
>refer to are 10 year olds.
I saw one in operation in an engineering prototype lab in Minnapolis
quite recently, though it very probably was more than 10 years old.
Yes, most production has gone offshore. Not all in China BTW.
Don Foreman
wrote:
I'm starting to regret having mentioned tape.
I'm looking at a servomotor with stall (all day) torque of 0.734 N-m,
peak torque of 5.5 N-m. The whole damned motor weighs about 2.4 kg,
the rotor mass is surely less than half of that. Motor OD is about
80mm or 3.125". Do you think this motor could accomplish Tom's task?
I think it could do it easily and for a very long time.
Martin H. Eastburn
and they have a sister site in Mexico. These are power line xformers.
Martin