Learning by Doing

[elevmike]

Mark,

I think I remember you posting something about your feed cutter?? If so didnt it cut with a rotating or moving cutter? The shear in this project is stationary, so if the wire dosent stop before cutting it will likely fold, or kink.

Glenn,

Thanks I'll check that out!

Regards, Mike.

 

[Rube]

Mike, the shear on our feeder was a levered, almost scissor-like, cutter but it was fast as hell. There was a very slight bucking as the shear cut the wire but we were cutting long enough lengths that the bow was absorbed in the feeding wire. The shear and continuous feed would indeed depend on the feed speed and shear speed. Slow feed with a fast shear would prevent the feed from having to stop.

While I'm at it, another way to prevent using steppers is to use a clutch/brake setup to the drive wheels. This is only an alternative since i don't much care for clutch/brakes.

 

[ArikBY]

pstephens

Welcome to our community.
Let me join to Ron & Bitmore,I love the way you writing.

I dont know if you plan to use straightening wheels as Rube mentioned,I think it neceessary.Otherwise you will get "curves" in the end of the roll.
As I saw in the last posts some methods mentioned how to do your application.
Servo steper open loop closed loop ect..
My question is how many pieces per minute you want?
For 10 pieces fer minute Rube idea with limit SW is the best,You can pull very slowly "hit" the SW and cut.
If you want 100 per minute you need servo with cut on fly system.
So let us know what the rate you want.?
With this figure you can get the best solution.
Another issue.I think you need "Rewinder". 500 leb(240Kg) is pretty havey roll to pull and cut.
The simplest system is with feed motor and 2 sensors.Up to systems with loadcell magnetic brake ect.Again it depend on the quantity per minute.
I think you chosed the right PLC which will give you solotion for almost all control option for this application.

Feel free to ask any quation you want.
I am working right now on machine with similar application like yours with paper instead of wire.VFD and 2 sppeds.
I use DL06 too, with High Speed Counter.if you want to have a look at that, let me know I will translate it for you(the comments written in Hebrew).
Good luck.I am sure you will successes.

 

[Doug-P]

I used to work with a similar machine and our wire was fed thru some straightening wheels before it got measured and sheared. The straightening wheels were driven nonstop and the wire was sheared on the fly. The wire triggered a limit switch on a spring-loaded, "get out of the way" plate at the end of the machine's tray. When the plate moved due to being pushed by the advancing wire, the shear cut it, and the plate sprung back home. The Limit Switch was eventually replaced by a photoeye.

I don't know if this is a viable solution in your case but your photos tend to make me think it is. This would save installing a stepper motor and the required controls. Of course this all depends on how fast the shear is as well.

This is what I was indirectly driving at with my previous post.

pstephens - I too acknowledge your writing and explanatory powers. In fact, I think a link to this thread should be posted in the FAQ section under the heading "How to phrase a question".

Going on: Would it be feasible to add a drive motor to run the feed spool? If so, this would ease the requirements for the feed/stepper motor

 

[pstephens]

A carefully selected stepping motor still remains a pretty good choice in lots of projects. I have been in the field for years and the number of applications always seems to be endless whatever you think about.

I strongly agree! The idea of a compact, variable-speed, rotary actuating device, that moves in discrete, digitally controllable steps is hard for a machine designer to pass up. We need to be aware of the limitations, however, and design accordingly.

The load inertia plus your drive mechanism should deserve a quite strong motor. Did you experience the required starting torque?

This is probably my main concern at the moment. I'm holding back on selecting a specific motor, for now, as I plan on spending some more time at my customer's plant, running the existing machine, and getting a better "feel" for how the material acts and handles. My customer has also ordered one of the 500 lb. rolls of wire, so I can get more precise dimensions and calculate the inertia more accurately. I also plan to check the pulling tension on the existing operation with the 100 lb roll, perhaps to make a preliminary calculation for the 500 lb roll, as the inertia should be directly proportional to weight (given that the radial dimensions are at least similar.)

If you plan to keep working in NEMA34, ask PacSci for quotations among their Sigmax K3x series (select 8 leads / K types). As a matter of fact, extended prices should reflect some hugely extended capabilities. But this will allow you to get high torques while dealing with mid-range voltages (less than 90V)/currents and a low-cost homemade power supply (compared to bigger motors often requiring up to 130/160VDC). Open frame OEM drives up to 12Amps or metal housing types up to 12/14 Amps may be easily found.

Thanks for the info! I've been checking out their website, and it's comforting to hear from someone that has experience using their products. Right now, my gut tells me that my torque requirement will put me somewhwre near the top end of the NEMA 34 category and the bottom end of the NEMA 42. I will be getting harder data on this in the near future.

As far as no micro-stepping modes are involved, any PLC with a dedicated pulse function (solid state output is mandatory!) including manageable accel/decel will suit this project with peripheral I/Os rather than an indexer.

From my limited understanding of the subject, it seems that micro-stepping does not really improve resolution, as the rotor is trying to stop at an "unnatural" position. I would not plan on using micro-stepping for any purpose other than to smooth the rotor movement. Are you saying that I would not need to purchase one of those hi-speed counting modules, like the HO-CTRIO, for this application?

pstephens

 

[pstephens]

Since you're not moving all that fast, you may want to try it first without an encoder. If you find it isn't repeatable, then adding an encoder will allow the PLC to make up for the missed steps, slippage, etc.

That makes a lot of sense, and it's something that I hadn't considered. Some projects don't lend themselves well to this kind of "re-work" provision (mainly depending on who the customer is), but this particular customer would probably not have a problem with it.

Open-Loop:
PLC: "Give me 60 inches of wire"
Response: "I'll try, but I won't make any promises"

Closed-Loop:
PLC: "Give me 60 inches of wire"
Response: "I gave you exactly 'x' inches of wire"

Very well put!

 

[pstephens]

My opinion may or may not hold much validity... You have done what most other questioners have not,,, your homework and investigation! It would be a joy to me to have other users/viewers with the same amount of enthusiasm as you!

I think that your opinion on this is most valid, and I thank you for the acknowledgement!

My next thought is... Are you looking for a job? I can certainly use a person like you! Good luck with all of your ventures (heck it's just good engineering), and may God bless!

I'm not currently looking for a job, but I'm always looking for work! (It's nice if one can be selective!) Thanks much for the vote of confidence!

pstephens

 

[Doug-P]

What operator??

I ask this because in post #6 there is what appears to be a narrow track or guide extending out from the shear. pstephens didn't address it but, I presume that the operator:

1. pulls wire along the guide until it reaches the adjustable stop
2. acutates shear
3. removes completed part from machine
4. places completed part with others in a collection bin for further processing

If the only thing added is a PLC, what happens to steps 3 & 4?

 

[pstephens]

Laurent is right about the stepping motor. You will need DC/solid state outputs to drive the setepper drive. You can add a relay to activate the shear.

I wonder if it's possible to drive a DC solenoid valve directly from a solid state output? Most of my experience has been with PLC's that have relay inputs and outputs. I'm accustomed to using solenoid valves with 120VAC coils, 120VAC motor starters, etc. Seems like the trend is toward more DC, probably as a consequence of more digital interfacing.

A small electrical mech brake on the support shaft of the reel might be in order. That way you won't have to pull through the friction device, lowering the demand on the motor, and lowering the possability for slip between the drive rollers, and wire. You also wont need as much pressure on the rollers which may lessen the impression left on the wire.

Excellent observation. I considered this early on, and have kept it in the back of my mind as something to fall back on. Actually, the preliminary drawing I submitted with my proposal shows a feed roll brake, but I have since been questioning the need. I've already budgeted for one, and I may be adding one before it's all said and done.

The rollers: You can make up a roller setup then get them treated with a friction surface like these people do here: http://www.surfalloy.com/ They have many grades and textures available, and I'm gonna guess that the cost would be about a few hundred bucks, based on my experience. With the right texture/grade surface, you wont leave much of an impression, if any at all, on the wire. This will also help to lower the power requirements of the drive, and wear on the bearings etc..

Great idea. This is something I hadn't considered at all, though I've seen it done before.

Go for feedback, (highly reccomended, Thank you Eric) it's really not expensive or complicated, mount the encoder on the ideler/pressure rollers to eliminate the possability of measuring slip and cutting short. In the case of elevators we place a tach/encoder on the motor to feedback to the drive...

I have to admit, I'm liking the idea of an encoder more and more. I think Gerry M had the best idea in recommending that the encoder be coupled to a separate idler wheel driven from the wire. This would isolate the encoder from torque load-induced slippage. The encoder would be reading directly from the movement of the wire itself. The only torque loading would be the negligible amount required to drive the encoder.

Question: are you going to use the existing sheer? It seems that you could, thus lowering the cost of the project, and allowing for more money for other stuff.

Definitely. That was my plan all along, and something the customer favors as well.

Thanks for the comments, Mike

 

[elevmike]

3. removes completed part from machine
4. places completed part with others in a collection bin for further processing

If the only thing added is a PLC, what happens to steps 3 & 4?

As the wire is fed through the cutter, the end drops into a bin/tray maybe about 12" below the level of the feeder and shear. the material is cut and the cut end drops into the tray.. The tray holds hundreds of cut wires.

 

[pstephens]

Re: quick sideline ...

I can’t make you a job offer, but I can guarantee that you could easily work in the technical writing field ... you write EXTREMELY well! ...

Thank you, Ron! I've always thought that being able to write well was a big help in convincing a customer to purchase my services. At least it might sound like I know what I'm talking about. But, as they say, "the proof is in the pudding", and you can only fool someone once. Still, some of the engineer-types at the larger companies seem quite impressed by clear, concise proposals. On the other hand, I've had customers that couldn't care less about writing skills. Reputation was the only thing that mattered.

 

[pstephens]

Originally posted by Doug-P I'm wondering, once this gizmo is 'automated', what's the operator's part?

As I mentioned earlier, this is an off-line operation. From what I can tell, there is no particular operator currently "assigned" to this machine. Batches of wires are cut as needed, by whomever is available to do the work. The operator now has to pull the wire from the roll by hand, till it hits a block of wood vise-gripped to that aluminum channel you see in the picture. That's the only purpose of the aluminum channel -- just to hold the length stop. When the wire is up against the stop, he actuates the valve to cut the part to length. Then he places the wire on a cart or in a tray (or on the floor, depending on the length.)

Since this is a spring-tempered wire, the shearing action tends to propel the cut wire very slightly out of the downstream blade. This makes handling the output from the automated process rather simple. We will probably provide a removable catch pan on the end of the machine to hold a good-sized quantity of parts, up to a certain length. Beyond that, the customer will utilize one or more wheeled carts, strategically placed to catch the sheared wires.

Automating this process simply means that it will run a specific batch (single length) of parts without the need to have someone standing there pulling wire off the roll, actuating a valve, and placing finished parts on a tray. Going to the larger roll of wire (which is not part of the "automation", admittedly) allows them to process more parts without having to stop and re-load the machine.

pstephens

 

[Rube]

Re: Re: quick sideline ...

Reputation was the only thing that mattered.

Well, I'm screwed

Oh, you meant work reputation. Whew.

 

[elevmike]

I wonder if it's possible to drive a DC solenoid valve directly from a solid state output? Most of my experience has been with PLC's that have relay inputs and outputs. I'm accustomed to using solenoid valves with 120VAC coils, 120VAC motor starters, etc. Seems like the trend is toward more DC, probably as a consequence of more digital interfacing.

I would strongly reccomend aganst using the DC output to directly drive the solenoid coil. The spike caused by the collapsing coil will surly smoke the solid state output device. You sould add a 24vdc relay (like a KH syle) that would inturn drive the 110vac solenoid coil. I say 110 VAC because youll get less arching and longer contact life etc.. (just my opinion)

 

[pstephens]

I used to work with a similar machine and our wire was fed thru some straightening wheels before it got measured and sheared. The straightening wheels were driven nonstop and the wire was sheared...[etc., etc.] I don't know if this is a viable solution in your case but your photos tend to make me think it is.

Yes, I've seen these kinds of machines. At a company that I used to work for, we did a lot of fixture work for Hoover Automotive Seating Division, in Georgetown, KY. They did a huge amount of work with formed wire, spot-welded into complex configurations, used in making seats for new cars. I remember visiting their plant one time and seeing many lines like you describe -- fascinating to watch!

The machine I'm proposing has a whole different set of design parameters. The wire is spring tempered, not soft annealed, and is straight just as it comes off the roll. It's really quite remarkable. As long as the eleastic limit is not exceeded in rolling up the wire (it's not, because they size the roll diameter just so), it comes off the roll just as straight as it went on.

I think that a machine like you describe would be extreme overkill on this application. Production rates are just nowhere near that high. That's why my customer can't afford to spend a great deal on this project. It's just a little operation sitting off in the corner that they fire up every couple of days to run the next few days' production. As long as it will run more or less unattended, speed is not much of an issue.