Torch Height Control Challenge

[rescueweasel]

I have a cnc plasma system and want to add Digital Torch Height Control but How?

The System 4 steppers controlled by Parker drives. All the Parker drives come together and are wired into one parallel port which connects to the only parallel port on the back of the computer.

I'm running Mach 3 and have control over my Z axis via the keyboard keys.
Mach 3 can control the z axis for plunge / cut height but does not have any feedback for arc voltage for digital control.

I dont have a BoB so the normal interfaces are out I think.

Anyone running a system like this or know how to adapt digital THC?

Thanks,

[jimcolt]

There are several stand - alone THC systems out on the market. By stand alone, the THC is completely independant of your software or cnc control. It interfaces electrically between the plasma and the cnc I/O. These were the first types of plasma height control and have been used widely since about 1975 or so!

Dynatorch has a system (www.dynatorch.com) that is probably the lowest priced for one of these, although I have seen a few Chinese advertisements for THC systems. Hypertherm has a few Industrial quality (read more expensive, more robust, designed to work at high duty cycle 3 shifts a day). www.hypertherm.com Look at the Sensor PHC height control on Hypertherms site.

A standalone THC has its own control panel with pierce height, pierce delay, cut height and arc voltage settings. The plasma start signal goes from cnc to THC, that starts the IHS (initial height sense) to find the surface of the plate, the THC then retracts to pierce height, sends start to the plasma, waits until the pierce delay timer times out, and an arc transfer signal comes back from plasma, then sends an ok to move signal to the cnc.

Jim Colt

[rescueweasel]

Jim,

Thanks for the great info. It looks like both could work for me but the price is just way to much for me. The Dyna Torch looked to be the least expensive at over $2,000. I'm on a tight budget (who isnt) but I'm trying to find decent quality at a much lower price (I know good luck)

[plain ol Bill]

Torchead on this forum has THC systems. Whether they will work with your set up or not I don't know. You can contact him through his website candcnc.com.

[rescueweasel]

I have looked at the products from candcnc and they are the right price range but because of my lack of a BoB and other interfaces its looking pretty complicated to make that work. I will have to download the manual and investigate more. If anyone has used there products and adapted them for a situation like mine I would love to hear about it.

[jimcolt]

I am not aware of any less expensive THC's....I'd love to see someone design, build and sell a full featured standalone THC for less......because they would sell a lot of them! CandCNC has nice THC systems.....but they not "standalone"....need specific software to operate.

The high end, high performance industrial THC systems sell for as much as $15,000 per torch.....so in comparison $2,000 is inexpensive. A good z axis slide with servo drive (speed, positioning accuracy, payload capacity) that is hardened to 3 shifts/day plasma dust and molten metal splatter, as well as water spray can cost more than $3,000 to build.....and that does not include electronics and interface hardware.

If anyone is interested in designing a THC, I'm happy to provide minimal details of the requirements that a plasma torch needs for best cut quality as well as best consumable life.

Jim

Originally Posted by rescueweasel Jim, Thanks for the great info. It looks like both could work for me but the price is just way to much for me. The Dyna Torch looked to be the least expensive at over $2,000. I'm on a tight budget (who isnt) but I'm trying to find decent quality at a much lower price (I know good luck)

[Torchhead]

Originally Posted by rescueweasel I have looked at the products from candcnc and they are the right price range but because of my lack of a BoB and other interfaces its looking pretty complicated to make that work. I will have to download the manual and investigate more. If anyone has used there products and adapted them for a situation like mine I would love to hear about it.

1. Add in a second parallel port to the PC and buy a simple low cost non-powered BOB for it to get to the inputs.
2. Buy the LCTHC.
3. Hook up the three needed input signals to the 2nd port. Use one output to the LCTHC to fire the torch.

OR:

Get the MP3000-DTHC with the built-in UBOB and rewire your motor drives to the MTA150 card that comes with the MP3000-DTHC. I have helped a couple of guys build tables with older Parker Drives. there is nothing special about the interface. They use opto inputs for step & dir and a common and that's about it. Get the MP3000E manual off the website and look at the drawings for hooking it up to drives like the Gecko's.

You already have 90% of what you need (3 axis of motors, drivers, all running with MACH.) Hundreds of guys have built plasma tables with a lot less to start with.

At MOST you will be out less than 600 bucks (a LOT less if you go the LCTHC direction).
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...I'd love to see someone design, build and sell a full featured standalone THC for less......

Bless you Jim (Colt), but I don't think the world needs another stand alone THC solution. There are just so many compelling reasons to have the THC involved in the tool path motion (not the least of which is lower cost).

Thanks to your inspiration (earlier post about some of the advanced features the high dollar THC's have) we have added a "Smart Cut" feature to the DTHC that will use the first second or two of a cut to "teach" the DTHC the right Target Volts (Preset) for the cut. You have the option of doing it at the first of every cut or at the first of a job. It was relatively easy because the application (MACH) exchanges constant information with the DTHC and allows reading, averaging and setting a voltage on the fly. Since it's all in software, nothing has to change but the MACH Plug-in (driver program). It will be a Free upgrade for all MP3000-DTHC and BladeRunner AIO Dragon Cut owners.

I haven't said much about it lately because it hit a few snags and had to be redesigned, but the Digital Current Probe (DCP) project is now past the prototype phase and in pre-production (I released the order for first run of PCB's Friday) . It will give accurate (2%) real time current readings off the workclamp (DC current) from 20 to 200 amps that will readout on the screen next to the Torch Volts, and give the operator options to set warnings (and optionally fault and stop the cut) if the cut current is a percentage above or below the preset value. Forget to clip on the workclamp and it will stop and warn you, forget to change the current setting knob with a nozzle change, and it will remind you. Have bad cuts and can't figure out why? Maybe the cut current is not what you think.

It is also used for ARC OK signal (adjustable) so any plasma cutter can be automated. Units will measure up to 150A (200A at slightly lower accuracy) and handle a 400A over load with no damage. The probe sends the current to the DTHC using PWM it make it noise immune.

SOMEDAY, if plasma manufactures can make access to the current setting a remote signal (i.e. 0-10VDC analog) like most industrial VFD's do. then it would be easy to let the software preset (or change on the fly) the current setting. Maybe Hypertherm could lead the market (again) and make that feature available on the smaller air plasma machines. Other plasma manufactures are just NOW starting to wake up and realize that smaller air plasmas are being used for automated cutting. (duh!).

All of the DTHC innovations would have been a colossal PITA if the THC were not integrated in as part of the motion control system and screens.

TOM caudle
www.CandCNC.com
Totally Modular CNC Electronics.

[jimcolt]

Tom,

Thats great that you now have the sampling function to help automate the THC. It is kind of funny because Thermal Dynamics had "sample and hold" on one of their THC's back in the 80's....but the problem likely was that the circuitry and feedback loop had a rather slow response....so it never worked very reliably. Now....it would be nice to see you add "ohmic contact", but keep the limit switch IHS as well. The ohmic is unbeatable on clean dry surfaces, and causes no deflection on very thin gauge plate. On plate that does not deflect easily (say over 3/16" or so) use the floating head switch, on thinner with clean top surface use the ohmic function...just a thought!

In regards to standalone, with our 4 current models of THC systems, about 75% of what we sell are standalone systems, meaning they will work on virtually any machine/software, and the annual numbers are in the thousands.....so we'll stick with that line of thinking! Of course we also have versions that are integrated into the cnc and even the CAM....absolutely the easiest to use, but don't fit all machines.

And, Tom.....the new Powermax65 and 85 have a serial data port (optional) that allows you to remotely adjust current and air pressure on the fly...if you wish. It also provides diagnostic codes to put pretty much all control of the plasma system on the cnc. We've been doing this for years with the industrial systems, now we have developed a lower cost technology for air plasma. With this feature, and a little experimentation, you can adjust current with speed, which may improve hole quality and corner dross, etc.

Jim

[Torchhead]

Originally Posted by jimcolt Tom, Thats great that you now have the sampling function to help automate the THC. It is kind of funny because Thermal Dynamics had "sample and hold" on one of their THC's back in the 80's....but the problem likely was that the circuitry and feedback loop had a rather slow response....so it never worked very reliably. Now....it would be nice to see you add "ohmic contact", but keep the limit switch IHS as well. The ohmic is unbeatable on clean dry surfaces, and causes no deflection on very thin gauge plate. On plate that does not deflect easily (say over 3/16" or so) use the floating head switch, on thinner with clean top surface use the ohmic function...just a thought! In regards to standalone, with our 4 current models of THC systems, about 75% of what we sell are standalone systems, meaning they will work on virtually any machine/software, and the annual numbers are in the thousands.....so we'll stick with that line of thinking! Of course we also have versions that are integrated into the cnc and even the CAM....absolutely the easiest to use, but don't fit all machines. And, Tom.....the new Powermax65 and 85 have a serial data port (optional) that allows you to remotely adjust current and air pressure on the fly...if you wish. It also provides diagnostic codes to put pretty much all control of the plasma system on the cnc. We've been doing this for years with the industrial systems, now we have developed a lower cost technology for air plasma. With this feature, and a little experimentation, you can adjust current with speed, which may improve hole quality and corner dross, etc. Jim

Well, electronics has changed a LOT since the 80's! What used to take complex circuitry to do sample and hold is now a few lines of code in firmware. I'm an old power and analog engineer but I have come around to the world of embedded processors and tiny surface mount components.

I am working on an isolated Ohmic contact/collision detection retro fit for any torch. It will be in parallel with the mechanical touch-off so either will function. Biggest problem now is the best way to do a universal pickup. I just bought a boatload of Lithium batteries (rechargeable) that will run the ohmic sensor for over 1000 hrs per charge. We use total isolation in our systems so the machine inputs (Homes, limits, probes, etc) are NOT referenced to the noisy Plasma table ground. That keeps ugly noise and spikes out of the PC inputs. The problem with ohmic sensing is it's unreliable on dirty material and if you use the conventional method of using the metal workpiece as one side of the circuit, that instantly makes the normally floating inputs all tied to the table. If the table is poorly or not grounded locally with good earth grounds, then the potential for getting plasma spikes and noise into the inputs (like for e-stop) is greatly enhanced. One of the reasons a lot of vendors won't support HF (and CD start) plasma systems is they don't control the separation of the grounds. It's real disappointing for the controller or the PC to fault or freeze when the cut starts or ends! On a stand alone controller you make the entire controller "live" at the plasma side ground since there is no communication back to the controller, but it's death to low level logic to tie it to the plasma workclamp potential.

It's (really) good news on the serial interface. Is it RS232 or the more robust RS422/RS485? At the least we would need to build an isolated serial link (see comments above on sharing grounds!) We have experience with both. Where can I get the technical specs and build an interface? Does it have DC Current feedback? I can generate a special POST for SheetCAM that will let the user define Current presets when they build the toolpath OR use a Cut Profile to define and set it automatically.
We can make it part of our control electronics for the 65 and 85 users. (it would be neat if you extended the option down to the 45 too) I get asked almost daily for recommendations for plasma cutters. I try to be objective and point out the pro's and cons of each brand. Every time Hypertherm makes an automated feature available it tilts my suggest more in that direction.

It's also pretty easy to predict tool path trajectory and put in automation signals if we have access to controlling cut current. We can control target voltage on the fly. We also have access to the actual true feedrate as it cuts. The CAM method looks at the code and through math knows where the tight turns and corners are and where a change in cut current or target voltage can be applied. The problem I have right now is knowing how much to adjust the parameters (like a cut chart but for different feedrate speeds).

I know there is a market for stand alone THC's in the industrial market but while 75% of the HyperTherm market is in that segment, over 90% of our market is the small shop, and home user side. I have no desire to get into the industrial controls side (been there, done that) It's our goal to make the technology available at a reasonable cost. This whole market segment did not exist a few years ago. It opens up opportunities for sales that just were not there before. That includes smaller plasma cutters.

Keep makin' sparks!

The Smart-Cut feature will be available for download next week. We still have some final testing to do.

TOM caudle
www.CandCNC.com

[jimcolt]

Tom,

Our engineering group is putting together a white paper describing the correct interface with the serial data.....when it is done I will make sure you get an advance copy. I don't belive there is current feedback, just your end setting the current, and air pressure. I will find out the type of serial it is as well...

Jim

[Torchhead]

Originally Posted by jimcolt Tom, Our engineering group is putting together a white paper describing the correct interface with the serial data.....when it is done I will make sure you get an advance copy. I don't belive there is current feedback, just your end setting the current, and air pressure. I will find out the type of serial it is as well... Jim

Thanks Jim. we can use the upcoming DCP to measure actual cut current and adjust remotely to hold a value OR change it based on tool path and feedrate. As you know plasma is about power (watts) into the cut. The three components of power(heat) are Volts and Amps into a load (resistance or in this case the arc gap and material)

Your are welcome to contact me off-list ; tom(at)CandCNC(dotcom)

TOM caudle
www.CandCNC.com

[rescueweasel]

Thanks for the info, I'm going to download the two manuals and see which one will work best for my situation. Its sounding a little out of my league (still learning) so I may be back with more questions. I would love to find someone who had been in the same situation for some guidance.

Thanks,