Feeding-wire sensor for wire-knitting machines. Relay circuit in mind. 3

[MechCal]

Hello, I'm a wire-knitting machine operator with very little knowledge on circuits. I want to install a system on each one of the machines so that when one of the wires feeding the machine breaks the machine shuts down.
My idea is to install a low voltage circuit that is closed with the wire being knitted(.011" and .006" 304Lss wire), so when the wire breaks it opens the circuit de-energising a relay coil, thus opening a NO contact connected in series with the power source, shutting off the machine.

Some questions I have:
-Is my idea feasible?
-How can I get the power for this low voltage circuit? What kind of components do I need? The machines have 180VDC motors and my power supply is 220VAC.

Any comments will be highly appreciated. I got many machines and a solution to this problem will decrease the downtime a lot.

Thanks a lot.

 

[VEBill]

It's basically a sensor question. Once you have reliable wire breakage sensors, then rest is relatively trivial.

The most obvious sensor would be two contacts bridged by the metal wire. The less obvious problem is that it might not be sufficiently reliable. Metal on metal contacts are a science unto themselves, not to mention wear out.

A better sensor might be something activated by weight or tension. Then you simply string the wires through the loops and they apply sufficiently force to activate a simple switch. Obviously this is going to require N sensors where N is probably a large number.

Perhaps there's a way to detect any broken wire when it falls down, and then one sensor per machine might be possible.

Whatever sensor you use needs to be wired into an intelligent circuit that imposes a time delay before reacting.

 

[MiketheEngineer]

I think the low voltage method may be problematic - currents could find their way around all kinds of directions and even if the wire broke - you would not be able to sense it.

Weights or tensioners as suggested might work. Optical sensor may be another method.

Get some help from someone experienced in this area. You are working with some pretty good voltages and large motors.

 

[Compositepro]

This is usually done on looms using "drop wires" (Google). Every yarn passes through its own drop wire which is often made from thin sheet metal. When a yarn breaks it drop the drop wire and one sensor detects if any wire has dropped. There are many ways to accomplish this. That is what engineers do. You should discuss this with engineering or maintenance in your own company. Your basic idea is good.

 

[MikeHalloran]

I'll bet that your knitting machines once had a broken wire sensor of some kind, and that it was such a hassle with parts wearing out or nuisance shutdowns that it was removed or just bypassed. Ask an old operator.



Mike Halloran
Pembroke Pines, FL, USA

 

[mcgyvr]

Simply micro switch with an arm application.. The arm is held down by the wire.. When the wire is not there the arm flips back up. Wire the switch to a relay. Use the contacts of the relay to shut down the machine. Simple.. requires a micro switch, relay and small wall wart type power supply to energize the relay.

 

[MechCal]

Wow, thank you so much for all you inputs. I certainly like the idea of the tension sensor using a micro switch, a relay and an AC adapter plugged to the wall. It will ease the electrical connections too.
I'll go from here for now...thx

 

[VEBill]

If you're going to try a very simple system, then at least consider the start-up sequence. Imagine if the wires are loose at start, and you can't get the machine started. You'd at least need a manual bypass switch to get it started.

Etc.

 

[mcgyvr]

The devil is always in the details...
Momentary dead man type bypass is a good suggestion if needed.

 

[MechCal]

Hello,

Thank you all for your answers. Attached is the circuit diagram I came up with. As a I told you before I don't know much about electric circuits, but my idea it to have everything ready for the electrician to come in and hook things up.

The relay and the lever micro switch (to work as a tension sensor) are these.

Switch: Z-15HW78-B (Omron)
SS Relay: CSW2410 (Crydom)

The motor is 180VDC, 5amp.

I'd really appreciate your comments on the circuit and components.

Thanks.

 

[VEBill]

If there is any danger that the wire tension varies during normal operation, then a momentary variation might trigger the circuit. This is where the time delay I mentioned earlier would potentially help.

But if that's not a problem, then... ...it's not a problem.


Should you add a key-operated bypass switch in case it doesn't work and you require production to resume while you troubleshoot?

 

[MechCal]

Hi VE1BLL, Thank you for your thread.

I don't think the wire tension variations will be a problem since the wire will pass through a loop at the end of the switch lever. The only possible way to trigger the circuit should be by wire breakage.

The key-operated bypass I think it's absolutely necessary. I’ll include it in the circuit.

Thank you for your inputs.