Next project; deja vu

My latest machine went into full production with a few minor glitches as
expected but it has joined the team. I now have to start a duplicate that I
hadn't planned so soon. Good thing, I guess. So, here are the first of
many ideas for improvements I want to incorporate.
Problem: Feed three strands of .110" x .017" wire, 3 to 4 inches in 200-250
ms. This is now done with an air cylinder pushing one-way clutched rollers.
It works ok but is persnickety getting the roller tension just right. It's
a bitch to make the rollers and they wear out in six months and spoo is a
factor in the clutches.
New idea: Imagine a DC gearmotor with a brake driving a pair of 3" dia.
intermeshing gears. The gears have a grove cut deep in the faces. The
gearmotor drives one gear and an air cylinder forces the gears together with
variable force. The wire rides in the groove, pinched between the gears. I
know this works. It's dirt proof and holds and pushes the wire well. The
question is how to control the gearmotor. One idea is to put a 12 volt
potential on the machine and the wire and insulate the adjustable wire stop.
The gearmotor starts from a cam operated switch and stops when the wire hits
the stop, using a relay. Another idea is to use a proxy on a chopper wheel
and a counter that stops the gearmotor. I would greatly appreciate any
other ideas! (See if you can guess which of the above is my idea.)
Reply to
Tom Gardner
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This looks like a great spot for a servo motor and control. I'd suggest Compumotor brand. You could easily set this unit to feed very accurately the length you need quickly every time it gets a "go" contact. I've worked with this company, their tech. service is great.
Karl

Reply to
Karl Townsend
couple of examples: small one:
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bigger one:
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Reply to
Karl Townsend
Use a servo motor with encoder. The servo control program acellerates the motor, travels for a planned distance, and then decelerates, stopping at the desired position. The only way this can get out of adjustment is if the gears wear down in diameter, or the wire slips.
That's the way I'd do it, anyway. But, then, I make this stuff, so it makes sense to me.
Jon
Reply to
Jon Elson
Tom,
Is this device purely to cut the wire, and after the cut the wires fall into a container? If so, do you have to stop the wire moving? Could you keep the wire feed running at a constant speed and have a snipper of some kind which quickly cuts through the wire at regular intervals of time? This is my first thought for the machine.
Best wishes,
Chris
Reply to
Christopher Tidy
Tom,
For very RELIABLE and precise feeding check out the air feeders used extensively on punch presses. These feeders are fast and can easily adjusted for different feed lengths. They also come in different sizes and one may be, hopefully easily, modified for your anticipated application.
Regards,
Wolfgang
Tom Gardner (nospam) wrote:
Reply to
wfhabicher
Does the wire have to stop? What about never stopping the feed?
As the cutter arm comes down, another arm between the cutter and the feeder could press on the wire. This would create a bend which would briefly take up the slack from the feeder as the cutter goes through and retracts.
Or perhaps a flying cutter. I think I saw this on a roll-forming machine. The die for punching holes in the rolled form would actually synchronize with the motion of the material as it pierced, and then retracted. Once the punches were out, the die would slide back to the starting position.
Obviously the advantage of not stopping the feed is faster production.
Regards,
Robin
Reply to
Robin S.
Does the wire have to stop? What about never stopping the feed?
As the cutter arm comes down, another arm between the cutter and the feeder could press on the wire. This would create a bend which would briefly take up the slack from the feeder as the cutter goes through and retracts.
Or perhaps a flying cutter. I think I saw this on a roll-forming machine. The die for punching holes in the rolled form would actually synchronize with the motion of the material as it pierced, and then retracted. Once the punches were out, the die would slide back to the starting position.
Obviously the advantage of not stopping the feed is faster production.
Regards,
Robin
Reply to
Robin S.
"Tom Gardner" wrote in news:t_0Qg.3384$ snipped-for-privacy@newssvr13.news.prodigy.com:
Servo. You probably already have a PLC for the machine, so installing a servo would not be that big of a deal. Extremely controllable, programmable ramp and decel, very accurate and very reliable. Not sure what kind of plc you are going to use, but this would lead you in the direction of a servo brand. The last one I built I used a S200 Siemens PLC (expandable) and an Indramat Servo and motor package. Relatively inexpensive. (PLC is about $300, extra I/O modules are like $100, and I would have to get the price of the servo, but it wasn't too bad. IIRC the planetary reducer was more than both put together.)
Reply to
Anthony
"Tom Gardner" wrote in news:t_0Qg.3384$ snipped-for-privacy@newssvr13.news.prodigy.com:
BTW, if you are just cutting wire, a roll cutter would let you feed continuously.
Reply to
Anthony
Nope, the wire is held firm after the cut and folded in half and stapled into a wood block, at about 80 rpm.
Reply to
Tom Gardner
Hey Robin! The machine cuts the wire and folds it in half and staples it into a wood block. The wire feed and cut has to happen in a time window when everything else is out of the way.
Reply to
Tom Gardner
Simpatico. I did accumulate servo motors, a Compumotor 6k controller, power supplies and just about everything to do the last machine full CNC. The brush table is a simple X-Y movement and the wire feed would be the third servo. I went full mechanical using cams to move the X-Y just because I knew the machine would only have to make one product and wouldn't have to change it. Also, I already had the cams. I think you're right; I should go full CNC on the next one and that solves the wire feed. It's a whole lot faster to do it full mechanical because I still have a lot to learn about the CNC stuff.
Reply to
Tom Gardner
I would turn this around. Keep the machine and wire well grounded, and isolate the stop. Use a 10-volt control transformer and relay wired so the relay closes when the wire completes the circuit by touching the electrified stop plate. This should be relatively dirt-proof.
Alternately, use one of those commercial inductive (electromagnetic) proximity sensors to signal when enough wire has been fed out so the tip has gotten close enough to the sensor. These sensors are completely dirtproof, and do not attract iron debris.
Joe Gwinn
Reply to
Joseph Gwinn
If you don't want to go servo try a geneva solution.
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Wes S
Reply to
clutch
Avoid all the suggestions of servos, encoders and gear motors, they will over complicate the issue and decrease reliability. You're on the right track with the nice simple easily adjustable and quickly replaceable air cylinder idea, the problem is just the gripper mechanism.
I'd suggest that instead of complicated and gunk prone one way bearings and rollers, you go with serrated gripper pads under moderate spring clamping tension. Two sets of these grippers, one fixed to prevent pull back and one cycling by the air cylinder to do the incremental pushing.
The serrated gripper pads would be a bit like the gripper pads in a pipe wrench with just a simple sawtooth design for one way gripping. I know I've seen ready made pads like this in either tool steel or carbide, but I'm not sure where. Someone should be able to point you to a source. Carbide should certainly last a good while and be easy to replace if they are a standard item.
You save all the complexity of servos and electronic controls and maintain the simplicity of length adjustment with manual stroke stops. You may also be able to retrofit the new design onto the existing machine if it proves to be better.
Pete C.
Reply to
Pete C.
Hmmm!
Reply to
Tom Gardner
Tom, does the wire length remain constant, or does it need to be adjustable? I just completed a mechanical cutter for .048 x .5" C1050 flat that used two rolls, spur geared together for the feed. Bottom roll is smooth, top roll knurled, with around 90 degrees of the top roll rim cut away. Circumference of uncut portion of top roll is feed length. During the 90 degrees of "dead time", a cam on the end of the shaft operates a cutter. Bulletproof so far.
If you need adjustability, look at the feed system on a Ideal or Sig-Node box stapler. Basically 2 cams with adjustable timing. Also a stapling operation in the cycle. Don't re-invent the wheel if you don't have to.
Reply to
Bill Marrs
Sleeper & Hartley spring winders also use a purely mechanical 2-cam adjustable feed. One cam drives the advance thru an adjustable eccentric. Feed length is determined by the setting of the eccentric. The second cam actuates the clamp. Both cams are two pieces, sandwiched together and clamped to a hub, so that timing and dwell can be adjusted without changing cams.
I'm with Pete in that I don't see any reason to use a servo, but I'd avoid air as well if a entirely mechanical system is practical.
I've done a lot of Sleeper tool design for one of my customers over the last couple years. They've got several machines that must be 50 years old, and once set up they just chug away with very little attention.
Ned Simmons
Reply to
Ned Simmons
"Tom Gardner" wrote in news:zx8Qg.3332$ snipped-for-privacy@newssvr11.news.prodigy.com:
It will be faster to do it CNC, imho. The additional beauty is if you want to make a product mix, change-over is very simple and fast. You really don't even need true CNC, you can run it from the PLC with just a panelview or such to input variables with.
Reply to
Anthony

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