[armitage]

Torchmate has suddenly started running its cut path before touching off going to its start location and doing a pierce cut. The torch comes down as it's running its path and starts cutting when it gets close enough. Same with multiple g-codes old and new. It has voltage heigh control. I don't run this much at all so setting haven't become rote, but I was using it very recently without issue.
Any thought out there?

[joeavaerage]

Hi,
sounds to me like the machine has detected a 'touch-off' but without the touch-off having actually occurred. I assume the touch off is detected by an Ohmic contact?
I would check that circuit, I would expect you to find that the is a circuit despite the torch not touching the material.

Craig

[armitage]

Thanks for the suggestion Craig. I'll look into that.

[armitage]

Craig,
Apparently this system uses motor resistance to detect touch-off. I've made sure there isn't any undue resistance in the mechanism and there isn't, so I'm speculating that there's some sort of "short" in the electronic switching signal and normally open has become normally closed. I don't know if this kind of thing is in your wheelhouse, but I'm at a loss as how to track down this possibility other than checking that all the cable connections are solid.
I'm pasting below the information provided about how the system works but I can't figure out where this switching would be happening. The "Start input" connections seem a likely candidate, but I can't tell that this is only initiating the touch-off sequence or also the tool path. I'm thinking the "Start output" connections are for turning the arc on and off, but still not really clear.
Thanks for any thought you can put into this.
Glenn


PRINCIPLES OF OPERATION
It is important to understand how the system operates to avoid potential problems and to assist in diagnosing
operational errors or failures.
The THC (Torch Height Control) system consists of two main components, the lifter station and the control
console. There are two cables connecting the lifter station to the console and one power cord which supplies AC
for the console. In addition you will install 3 two conductor cables that supply information to and from the THC
system. The first cable from the CNC to the THC console tells the system to begin auto height sensing sequence
and initiate the cut. The second cable supplies the arc voltage to the THC from the plasma power unit to
determine the torch height while cutting. The third cable allows the THC to tell the plasma unit to fire the arc and
stop the arc when the cut is complete.
Upon power up, the THC will raise the torch and establish the “home” position. You may use the up/dn switch to
jog the torch up or down as desired.
Setting the auto / man (automatic / manual) switch to the manual position prevents cutting operation of the
plasma. In the auto position, the THC will operate the plasma and height sense sequences.
When the CNC closes its’ output contact to start the cut, the THC begins the initial height sensing sequence by
sending the torch down to the metal surface. The torch will “feel” the metal by applying 5-10 pounds of force.
When it senses that the torch has stopped moving, it reverses the motor and brings the torch back up to the preset
pierce height. This height is adjusted by the “Pierce Height” knob on the front of the unit and can be set up to ½”
from the metal surface. The THC then closes the plasma start output relay and tells the plasma to fire the arc.
After the arc is established, the THC will begin sensing and averaging the arc voltage. This voltage is compared
to the “SET” voltage. The set voltage is adjusted on the front of the console by turning the “Set Volts” knob
while observing the digital display. Note the selector switch must be in the “SET” position to read the voltage
setting. The THC makes corrections to the torch height to maintain the arc voltage within 5 volts plus or minus.
The set voltage may be changed while cutting to adjust torch height. In the “READ” selector position, the
console will show the actual arc voltage.

[joeavaerage]

Hi,
that technique of sensing a surface is not uncommon. It relies on the motor driving until it is stalled, ie up against a surface and then the motor current will go up dramatically.
The electronics measures the motor current and can determine that the current has suddenly increased.

The problem you face is that clearly the electronic current measuring system, whatever it may be is faulty and supplying an erroneous signal that the torch has touched off.
It could be the measuring circuit or it could be that the motor is drawing more current than it should be, thus its standing current is now in excess of its threshold current.
Either way without some electronic knowhow you are not likely to be able to do anything about it. Do you have an oscilloscope for instance?

Craig

[armitage]

Craig,Thanks for the clear and targeted reply. Makes sense to me. I do have an oscilloscope (and other electronics test equipment), but lack the know-how myself on using it. I'd guess that testing the motor draw is the first step so maybe that's not too complicated. I'm sure I can google it.
Thanks.