Rod's Spaceship Scratch Built Plasma Table

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robertspark
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Re: Rod's Spaceship Scratch Built Plasma Table

Post by robertspark » Thu Jul 11, 2019 7:00 am

Rodw wrote:
Thu Jul 11, 2019 6:16 am
reverse run which is used for error recovery which is probably a not a major impediment. Plasmac will auto sense if reverse run exists and configure itself accordingly.

Unfortunately, the release manager for LinuxCNC did not want to release the reverse run feature until there had been further testing so it will be in V 2.9.
hmm, now that is an interesting feature to add.

How does it work?

In UCCNC it works by
A) providing THC is enabled
B) providing M3 is active
C) tracking the arc OK signal

if the ArcOK drops out with both A+B are active, then the torch will decelerate to a stop, and backup to the ARC OK lost position and await a restart.
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Re: Rod's Spaceship Scratch Built Plasma Table

Post by Rodw » Thu Jul 11, 2019 7:17 am

To tell you the truth I don't know as I've never needed it to recover from a fault yet. I think it allows you to move back and forth as far as the last M3 while the machine is paused (which loss of ArcOK triggers). There are some controls on the GUI to control this.

There is a video on Youtube of a guy using a MPG wheel to move back and forth thru the gcode with reverse run active which is cool. Search for user Samco from memory. Because I have 3 spare axes on my pendant, I was going to try that one rainy day...

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Re: Rod's Spaceship Scratch Built Plasma Table

Post by robertspark » Thu Jul 11, 2019 7:20 am

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Re: Rod's Spaceship Scratch Built Plasma Table

Post by Rodw » Thu Jul 11, 2019 8:36 am

You found it. I was actually thinking about the UCNC algorithm.

I don't think the travel distance after loss of ArcOk is significant with LinuxCNC. Say I'm cutting 2mm steel at 2100mm/min (35mm/sec). Linuxcnc will sense the loss of ArcOK in 1 millisecond and if my X/Y Maximum Accelleration is 1500 mm/sec/sec (which I think is the rate we will stop at), I've not moved further than about 0.8 mm from the loss of the arc (Just enough to have some material to restart on). I guess thats one of the advantages of running in real time.

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Re: Rod's Spaceship Scratch Built Plasma Table

Post by beefy » Mon Jul 15, 2019 3:10 am

Hi Rod,

The ultimate would be reverse run to a certain distance BEFORE the flameout point. Then restart the motion but without torch switched on. You'd also need THC off for this of course. Then just a few mm before the flameout point, manually turn the turn on (assuming this would not cause a pause in motion). Once cutting again, manually enable THC again.
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Re: Rod's Spaceship Scratch Built Plasma Table

Post by Rodw » Mon Jul 15, 2019 3:44 am

This does not work for our config (and probably not for LinuxCNC). Our torch is turned on with an M3 and with it all of the probing etc. When a fault ocurs, we pause motion so to restart it is a resume, not a full restart,

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Re: Rod's Spaceship Scratch Built Plasma Table

Post by beefy » Mon Jul 15, 2019 8:07 am

Rodw wrote:
Mon Jul 15, 2019 3:44 am
This does not work for our config (and probably not for LinuxCNC). Our torch is turned on with an M3 and with it all of the probing etc. When a fault ocurs, we pause motion so to restart it is a resume, not a full restart,
Not sure if I'm understanding that correctly Rod. Are you saying that in Lcnc, an M3 is not simply a torch fire but also initiates a bunch of other things happening. For that matter is there no way to manually fire the torch while doing a dry run of the gcode.

In Mach3 and UCCNC for example there are things like "Run From Here" or "Set Next Line" which can be used to start a program from any point in the gcode file. Of course you may need to manually touch off and set the Z height first, and possibly manually set feedrate before starting these mid file runs, because certain modal commands may not be in place.

Just trying to get a feel for how Lcnc runs compared to what I'm used to.
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Re: Rod's Spaceship Scratch Built Plasma Table

Post by islander261 » Mon Jul 15, 2019 10:58 pm

Guys

I have used the reverse run feature in the PlasmaC branch many times now. It is very nice when recovering from torch break aways when you hit tip ups. I just back up to the point the cut ended (a manual button on the GUI) and start again. PlasmaC always probes after an error so no special height setting or manual torch firing required. I think the docs Phill and Rod have posted now capture most of the functionality.

PlasmaC shares the general LinuxCNC problem of poor run from here support. It should always work if you are starting a file over but I wouldn't call its functionality robust. The good reverse run saves much of the need for this. There is an open source fix for this but I have had no luck in persuading any developers to make it part of the main stream configurations ( it is far beyond my coding ability).

PlasmaC takes full control of the Z axis away from the Gcode. When setup correctly a M3 S? will start the probing and torch control sequence. It is hard coded in plasmac component, something Mach and UCNC don't have. The S block is need in all LinuxCNC configurations because of some hard coding, the value of the parameter can be anything when plasma cutting.

You can email me with questions Kieth as I have been using PlasmaC with great success since early May. I was initially very wary of letting PlasmaC have total control over the Z axis and torch firing but Phill C. (one of your country men) put in incredible work and made a really good product. This is the solution that I was looking for 3+ years ago when I started trying LinuxCNC.

John

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Re: Rod's Spaceship Scratch Built Plasma Table

Post by Rodw » Tue Jul 16, 2019 12:13 am

John, thanks for helping Keith out there. John knows far more about error recovery than I do. John has had a major influence on Plasmac and Phill in Melbourne had this knack of capturing all sorts of different ideas into one cohesive unit.

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Re: Rod's Spaceship Scratch Built Plasma Table

Post by beefy » Tue Jul 16, 2019 8:11 pm

Thanks very much John & Rod,

and John I much appreciate your offer of emailing. Got a bit better grasp of Lcnc operation with the M3 now.

So like me, Phill is also in Melbourne. I think there is something wrong with us poms. We escape the crappy British weather and come to the cold winter rain of Melbourne LOL. I was supposed to go to tropical Queensland (barrier reef and all that stuff) but somehow I ended up here.

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Re: Rod's Spaceship Scratch Built Plasma Table

Post by robertspark » Wed Jul 17, 2019 2:10 am

nothing wrong with the weather here.
crackin the flags at the moment
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Re: Rod's Spaceship Scratch Built Plasma Table

Post by Rodw » Wed Jul 17, 2019 2:12 am

This isn't my handiwork, but here is a sheet of 16mm cut with the Linuxcnc plasmac config.
fullsheet.jpg
Stefan who converted from another well known commercial controller often used on this forum said the THC was still very much required even on material this thick. I think the right hand corner shows why....

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Re: Rod's Spaceship Scratch Built Plasma Table

Post by Rodw » Wed Aug 28, 2019 6:40 am

Its been a while since I did an update here. Our LinuxCNC Plasmac config is jumping ahead in leaps and bounds. I've had the parts laying around for years and never made my scribe mechanism but I think I better get onto it soon because scribes are now supported in Plasmac. This is done a little bit differently then in other systems becasue LinuxCNC supports multiple spindles so its just a matter of loading a scribe tool from the tool table that applies the tool offset from the torch by using standard tool change M6 commands and then specifying the spindle to use in the M3 command.

Plasmac has also gained inbuilt support for hole cutting where overburn and velocity slowdown is supported.

For guys cutting thick material, there is also a pierce only mode so you can do all pierces in the job and clean the dross off the plate before cutting out the parts. Stefan has used this to cut full sheets of 16mm and it all worked perfect! Here is a simulated demo of this in action
https://youtu.be/2R8zMYsL_A8

While this has been going on, I've been working with Peter Wallace from Mesa Electronics and today I finally got some real cutting done using a Mesa THCAD-5 card for Ohmic sensing. Peter wrote some new firmware for my Mesa 7i76e board so it can support up to three THCAD boards so I have one to sense the arc voltage and another for ohmic sensing. This is managed by a component I wrote that runs on LinuxCNC's servo thread 1000 times a second.

So here is the hardware:
hardware.jpg
Parts from the right of the unconnected blue relay in order:
24 volt power supply with 500 volt isolation
390 K scaling resistor to give a full scale of 24.5 volts (overkill mounted using a Mesa BUS strip that has 2 segments commoned together.)
THCAD-5 with 5 volt range (these can handle 500 volts overvoltage indefinitely)
Earth clamp for THCAD ground to table via enclosure bolted to it.
This circuit is powered up when the control box turns on it is powered all the time

So with this setup, everything in the ohmic circuit is 100% isolated so we don't even have to worry about protecting the circuit from arc voltages. I will say it took a long time for Peter to convince me of this!

So when I did some testing I found that the ohmic voltage rose from 0 volts to 24 volts over Z axis travel of 0.04mm and the 24V opto isolated relay I have been using turned on at 7.5 volts and goes off at 5 volts. This is likely too sensitive in some situations. So with the THCAD actually reading the voltage as the torch shield comes in contact with the material, I decided to enable a probe signal once the voltage exceeded an arbitrary 18 volts.
As an added bonus, I decided to add what might well prove to be a totally useless feature but I knew the THCAD can read a bit more than its full scale so by having a 24.5 volt full scale range, we can turn on a pin if the voltage exceeds 24.5 volts. Becasue we are using a 24 volt power supply, the only way that can happen is if the torch is actually cutting! So we have this cool and very wanky indicator we can use if we want to.

So there was only one way to see if this would work so I unleashed it on a job with 110 pierces and it worked flawlessly!
parts.jpg
Even more amazing is I did not blow anything up as the circuit was powered for the full job!
The next stage of development for this is to modify the component so it turns on say somewhere between 18-22 volts and stays on until the voltage falls to say 1-5 volts so there is a big range of sensor hysteresis for nice stable sensing. I will add some GUI controls so we can vary the sensing sensitivity for different conditions. It will be interesting to see how this will work with a water table. That is the next step.

So becasue this circuit does not rely on any resistors and has such fine control over material sensing, I have decided to name this hyper sensing (which one wag suggested was ohmic sensing on steroids!)

One thing we heard was that with a water table, leaving the sense circuit powered all of the time could result in corroded consumables. Does anybody have any knowledge about that?

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Re: Rod's Spaceship Scratch Built Plasma Table

Post by Rodw » Wed Sep 04, 2019 3:56 am

On this thread viewtopic.php?f=103&t=28781&p=174194#p174194 I said I would publish the ohmic sensing circuit used in the
last post and here it is:
HyperSense DIagram (1).png
I thought this is so vastly different to Ohmic sensing that we are calling it hypersensing which as one wag put it is Ohmic sensing on steroids!

The 390K resistor scales the 24 volt power supply to 24.5 volts. Because of the isolation on the THCAD, it would not matter if you were using a lower voltage for field power becasue the probe signal is generated in software.

I've now removed all the old ohmic stuff I had and am using this in production now its that good!
IMG_20190831_173258 (1).jpg
Somebody mentioned that there seemed to be a lot of wires but in reality most of them are hooked to other hardware
IMG_20190902_083822.jpg
The Mesa 7i76e is in the bottom right corner and it has another THCAD-10 board mounted beside it to the left to measure the torch voltage. Setting the voltage divider board in the plasma cutter to 30:1 is perfect for the THCAD-10 as then it needs no scaling resistor and provides a 300 volt range.

The THCAD will come into its own with high frequency start plasma cutters where EMI/RFI noise can cause havoc.

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Re: Rod's Spaceship Scratch Built Plasma Table

Post by cuttinparts » Wed Sep 04, 2019 11:57 am

Clean crisp wiring Rod :Like Everything looks awesome. Nice job.

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Re: Rod's Spaceship Scratch Built Plasma Table

Post by robertspark » Wed Sep 04, 2019 1:41 pm

rod, I thought there was only one encoder input on the 7i76e , where is the second?

what is the advantage of using an thcad card?

I understand it will have an accurate analog input (effectively) via the encoder.... but it will still have a digital threshold voltage / setting to determine if the plate has been touched or not?

what is the advantage over a bog standard commercially available ohmic sensor that has a potentiometer adjustment to set the threshold and a digital output ??
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Re: Rod's Spaceship Scratch Built Plasma Table

Post by Rodw » Wed Sep 04, 2019 4:37 pm

cuttinparts wrote:
Wed Sep 04, 2019 11:57 am
Clean crisp wiring Rod :Like Everything looks awesome. Nice job.
Thanks, It got a bit messy after I added Ohmic sensing so I still need a bit of tidying up and get the cover back on the conduit :)

There is actually (hopefully) a bit of science in the layout to defend against noise, all the mains power stuff is in the top left, all the 48v to the stepper drivers goes around the top and the logic wiring is in the conduit above the motion boards. If I did it again I'd downsize the 24v and 5v power supplies and make more use of DIN rail mounts and DIN rail terminal strips.

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Re: Rod's Spaceship Scratch Built Plasma Table

Post by Rodw » Wed Sep 04, 2019 5:31 pm

robertspark wrote:
Wed Sep 04, 2019 1:41 pm
rod, I thought there was only one encoder input on the 7i76e , where is the second?
Aha! The THCAD only uses a 2 wire output attached to Encoder A. So Peter at Mesa wrote new firmware for the 7i76e and 7i96 that places 2 additional encoder A's on the Encoder B and Encoder Index pins on the boards. The firmware is available for download from the Mesa product pages in a Zip file. The file names end in "pl.bit"

robertspark wrote:
Wed Sep 04, 2019 1:41 pm

what is the advantage of using an thcad card?

I understand it will have an accurate analog input (effectively) via the encoder.... but it will still have a digital threshold voltage / setting to determine if the plate has been touched or not?
This project was based on a theory of Peter's that the THCAD might let resistance be calculated from voltage loss. He sent me the THCAD to experiment with. I found on my table there was no voltage loss with firm contact but approaching the material with 0.01mm increments, I saw the voltage increase from 0V, to 12V, to 18V, to 24V
I also looked at the 24V relays I was using and saw they turned on at 7.5 volts and off at 5 volts.

So I wrote a component that allowed an adjustable upper threshold (I chose 18 volts) and I am going to add another threshold at say 1-5 volts at which it will turn off to make sure we have a super wide switch hysteresis to avoid any spurious triggering.

To adjust sensitivity, it is intended that these thresholds will be able to be adjusted from the GUI screen.
robertspark wrote:
Wed Sep 04, 2019 1:41 pm
what is the advantage over a bog standard commercially available ohmic sensor that has a potentiometer adjustment to set the threshold and a digital output ??
None of us are using a commercial ohmic control with linuxcnc, just a couple of relays. But as I see it,

1. Costs are not significantly higher ( I removed AUD $60 in opto isolated relays and added an AUD $100 Thcad.)
2. Much simpler circuit, no need for diodes to protect from reverse arc voltage
3. no voltage loss
4. Instant sensing for faster and most accurate sensing.
5.no relays which are often quite slow to respond (have a look at the opto22 specs for example)
6. bulletproof in relation to arc voltages,
7. High noise immunity due to the THCAD design
8. Logic circuit is decoupled from the noisy plasma environment so no possibility that the ohmic sensing wire being used as an antenna to introduce spurious faults in a HF environment (eg 200 amp and above).
9. precise sensitivity adjustment

With the plasmac config after probing, the Z axis is lifted at the rate of 0.001 mm per millisecond (from memory) until the sensor turns off. I found the THCAD appeared to be faster with this final part of the probe. eg it touched and instantly rose to pierce height and fired.

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Re: Rod's Spaceship Scratch Built Plasma Table

Post by robertspark » Thu Sep 05, 2019 3:08 am

thanks rod for taking the time to reply, I see where your coming from now plus have a bit more food for thought
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