Blue screen AVHC

[MAS]

I have the blue screen Torchmate AVHC that I bought new.
It has developed a problem that I can't solve, that is it oscillates while cutting.
I look at the voltage display while the machine is cutting and the voltage goes up and down as much as 6 volts and very consistent.
I carefully went through the AVHC setup guide to adjust the unit so I don't think that's an issue.
The lifter station is 'like new' condition so I eliminated that part of it.
This 'sewing machine' effect does exactly the same with any amperage tip on any material.
Is there an adjustment inside the AVHC control box? I'm at my wits end with this thing.
On a long straight cut with a thickness of 3/8" or more you can see a wave on the underside of the plate caused by the torch going up and down.
My air pressure is fine, I have clean dry air, plasma cutter is grounded properly, and I installed a new ground clamp on the plasma cutter too with no effect. I installed ferrite chokes on the motor cable to the lifter station and that had no effect whatsoever.
I’m willing to bet that the blue screen control box is out of spec. I just don’t see what else it could be.
I’m out of ideas. Torchmate is not interested in helping me as I’ve contacted them several times about this.
Anybody out there that had this issue and solved it???

[gamble]

Did you call them? They don't always respond to email.

[MAS]

Yes Sir I did. They are very nice people but I think they just can't figure out what causing this problem.

[Gamelord]

I would check your earth ground. You may be getting some bad interference from somewhere.

[gamble]

Does your plasma have a HF start? I've heard of that causing issues

[MAS]

I have a Hypertherm 1650 machine, which is a nice unit.
If I switch to manual mode and run a cut, the voltage is completely steady.
What baffles me is it does this oscillating steady as a watch second hand.
I have the machine grounded to a 8' ground rod buried next to one leg of the table.

Mike

[WyoGreen]

I can faintly remember reading about a problem like this over on the CandCNC forum. It had something to do with how close you set the allowable voltage variation before the THC kicks in. If the voltage variation is set too low, then the THC goes crazy trying to raise and lower the Torch to keep the voltage in the set voltage range, thus the oscillation.

Hope this helps some, Steve

[MAS]

Steve, the Torchmate AVHC has these settings: arc voltage, pierce height, cutting height, pierce delay, sensing delay, pierce complete, and 'OK' to move.
Torchmate recommends to set the pierce to .1 sec and the sensing delay to .5 sec., these are when the pierce complete and OK to move are
enabled, when they're disabled then you have to set a time to pierce according to the particular tip and plate thickness.
That's about it. This thing oscillates like a Swiss watch, doesn't matter what tip you're using or type of material.
Thanks for the reply.
Mike

[islander261]

Mike

The TM tech help is good in my experience, how ever they are not the process engineers. I find that if you ask the correct question you get a good helpful answer. The frustrating part is when you don't know where you are going the guidance isn't too good sometimes.

I have hacked my AVHC and have a good idea about how they work. The voltage sense circuit is about as simple as it can get and still provide galvanic isolation from the arc current. The circuit has a .5s (2hz) single pole low pass filter that should get most of the HF noise. When you set your AVHC to manual mode does it hold the set height correctly? A good clue is put a Sharpy mark on the Z axis shaft coupler so you can see if it turns after it gets to the initial cut height. If it holds the height correctly then the problem is in the voltage sensing, this is most likely not news to you. Check the voltage sense wiring. Check both ends for secure clean connections, in your plasma power supply and at the AVHC. Make sure that the voltage sense wires do not run parallel close to the torch or ground connection cable. Check the connections between the plasma power supply and the table, again both the torch and the ground. Now if your plasma power supply is having trouble holding a constant cut current it will show up as a varying arc voltage and cause the AVHC to try and follow it. If you have a battery powered DVM connect it to the voltage sense wiring (keep the AVHC connected) and see if the voltage oscillates when cutting in the manual mode, danger don't do this if you aren't comfortable working with high voltages. If the voltage varies much then it is most likely your plasma power supply. I find that the measured voltage on my AVHC is way off from the book settings and I have to find the correct voltage for each set of cut parameters by cutting at a fixed current, cut height and speed using a test cut(s). I keep a cheat sheet in my desk of the measured results. I also set my sense delay to .9s gives better results.

John

[MAS]

John, thank you much for the reply, I will do these things that you suggest.
On manual mode the voltage readout is steady as can be, but when I go to auto everything operates
as it should EXCEPT for that constant steady oscillation. It's always exactly the same no matter what I cut.
the voltage swings up and down about 6 volts total steadily like a clock pendulum. I can see the lead screw
coupling turn back and forth about 90 degrees when cutting. If I cut a thicker piece of steel, you can see the wave
on the bottom side of the piece
I was reading you 'hack' post and you stated the torchmate unit uses a Cubloc CU280 PLC.
I went to their site and searched for that part number and it came back an empty search.
They have a CB280 but not a CU280.
Anyway thanks again for the info. When I get a change to try these suggestions, I'll
post here.

regards,
Mike

[islander261]

Mike

I forgot to mention that you need to eliminate any mechanical problems first. It sounds like servo hunting which can be caused by mild binding and/or backlash in the drive. Make sure your lifter is clean, well lubed (I use 3 in 1 oil)and not binding. The bronze drive nuts wear out, sometimes fast. Check the backlash on your drive. New nuts can be bought at Amazon (about $50) or McMaster (about $27) for far less than TM ( >$100). I think they are Nook brand. The lead screw is 3/8"-10tpi two start acme thread, this works out to .2" travel per revolution. I have replaced mine several times. The re assembly of the lifter is a real bitch to get it to move without binding. I had to lap in the nut from McMaster but the one from Amazon fit loose like the stock TM one. TM says to replace the nut and or drive shaft when the backlash approaches .1", I find mine doesn't work well when it is over .06", I get about .03" with a new drive nut installed.

I think you are correct about the Cubloc controller P/N. I don't know if the there is an integral term in the servo calculation but if there is and you have bad backlash it could cause the hunting you describe. The key here is the volts are good when manual cutting. I haven't found a way to suck the program out of the controller so I don't know what happens on the inside unlike the Smart Motor. When in the auto mode the control box sends correction commands to the lifter to try and keep the arc voltage constant. The commands sent to the lifter are in encoder counts to move so any backlash isn't compensated for. The Smart Motor also doesn't send any error indication to the control box if something doesn't work correctly, every Smart Motor subroutine ends with it sending an "OK" to the control box as a signal it is ready for the next command.

John

[MAS]

John, I guess I will be disassembling my lifter unit for a cleaning, inspection, and adjusting.
I'll report back probably next week.

regards,
Mike

[MAS]

John, I worked on my Z-axis today and it was a bit sticky so I cleaned, adjusted and lubricated to get it to work freely.
I have touch torque set at 12 and I have to add .03 to the initial and pierce heights to get the settings I need. The unit seems to be fine and all connections.
I'm beginning to think it's my hypertherm 1650 or torch or both causing this.
I don't know what to check for in the plasma unit or torch.
I found a video on my phone of the machine cutting some parts that I did 2-3 years back and I could see the lead screw coupling and it was steady, no sewing machine. I haven't changed anything on the machine since then either.
I did check the voltage in manual mode and it does if fact fluctuate but not like it does in auto.

Thank you for all your replies and help.
best regards,
Mike Scalise
McAllen, TX

[modelaratrod]

Look on pirate4x4.com in the torchmate forum and search for avhc porpoising there's a few threads and how they resolved it.

[modelaratrod]

http://www.pirate4x4.com/forum/125-torc ... cs/1052152