Messages

21

General Mach Discussion / Re: Physical buttons for plasma

« on: March 07, 2016, 05:33:42 PM »

Hi Hood,

for reasons of contamination I would consider having your gear rack on the outside and with the teeth facing down. As they are in the drawing you have gravity letting dust, etc settle on the teeth, as well as any sparks (abrasive slag) from the cutting.

The linear rails will be much easier to keep clean and lubricated but gear teeth are just a bunch of nooks and crannies.

Keith.

22

General Mach Discussion / Re: Computer died, starting over, what to buy?

« on: March 07, 2016, 04:28:35 PM »

Like Dave said, nearly all the older PCs with a built in parallel port have address 0378 as default.

Most of my PCs are Pentium 4, 2.8 to 3.2 Ghz. I spent a whole week a few months ago getting about 8 PCs installed with Mach3, plasma profiles loaded, etc. When it comes to older PCs I can never have enough spare, too many have just randomly died on me in the past. Saying that I think a lot of the "deaths" were due to failing memory sticks.

On a side note, I seem to have got the best Mach3 drier tests with Intel motherboards. Can't remember if it was VIA or SIS chipsets that someone said are known to be problematic with Mach3.

Keith.

23

General Mach Discussion / Re: Can other software be causing Mach3 cutting 'lag' issues?

« on: February 26, 2016, 04:30:15 PM »

Do a search on the forum for "optimisation" or "optimization". Should give you a little insight into installing XP for Mach3. Here is one:

http://www.machsupport.com/forum/index.php/topic,30566.0.html

Keith.

24

General Mach Discussion / Re: DriverTest Does Not Execute In Windows XP 32 Bit.

« on: February 24, 2016, 12:24:46 PM »

I've had this happen to me a few times with "new" PCs.

I've found that some PCs just don't seem to work with Mach3.

25

General Mach Discussion / Re: Yet again, UC100 issues

« on: February 11, 2016, 03:10:43 PM »

Too bad that support for XP is just about over.

Chas.

I dedicate my PC to running Mach and nothing else, so it never even gets connected to the internet. The updates and "support" have no meaning to me because I never need or use them. I just install XP on a formatted hard drive, do the optimisation, etc and away I go. If you can find a PC to run XP you could use XP for ever for just Mach.

Keith.

26

General Mach Discussion / Re: Physical buttons for plasma

« on: January 29, 2016, 05:54:53 PM »

Keith

I believe that your THC sample rate will determen how fast it can react to a voltage change. Too Slow and it caps teh speed of teh Z  early ??

(;-) TP

Electronics and computers can be super fast and assuming that is so, then the real limiting factor is mechanical, so let's have a think about this:

My theory is that the maximum USEABLE rate of a THC is completely determined by how fast a Z-axis can change direction then change back again. If you had a THC sample rate of say 50 times/sec then the worst case scenario is for 1/50 second the Z is being told to go up then for the next 1/50 second the Z is being told to go down. How many Z axis are capable of taking advantage of such demands.

I can easily bump up my sample rate to 100/sec and that's still giving me 10 milliseconds per sample to do all the calculations, compare with SET VOLTS, etc and give a THC UP/DOWN signal, certainly doable with my microcontroller.

BUT is there any benefit to reacting in 1/100th second when I can't see a Z axis being mechanically capable of taking advantage of that speed. I heard that a humming birds wings flap at about 50 times a second and when I see those little guys I can't imagine a Z axis competing with them.

And how long would be considered too long to wait for a THC UP/DOWN signal when the volts had gone outside of the SET VOLTS deadband range. My reasoning for NOT wanting to sample at such a high rate is that I can sample the voltage for longer periods and get better averaging of the noisy spiky plasma voltage.

Do you see my reasoning ?

Keith.

27

General Mach Discussion / Re: Physical buttons for plasma

« on: January 29, 2016, 03:02:35 PM »

Talking about overshoot, that's a problem that will be made a lot worse by having any delay in the control loop.

Has anyone ever came across any tests done to measure how long it takes from Mach3 receiving a THC UP/DOWN input signal to outputting the step/direction command to the stepper drive.

I'd assume that was programmed to be as "instant" as possible.

Keith.

28

General Mach Discussion / Re: Physical buttons for plasma

« on: January 27, 2016, 12:54:27 PM »

I'm still not convinced that ZERO acceleration is needed for THC.

There's a little goodie called deadband or hysteresis in a good THC. That acts as a buffer so if you deadband was +/- 1 volt, then so long as your accel/decel is fast enough it will at least keep the voltage within the dead band. Yeah, with accel/decel you'd pass the set point a bit BUT providing the accel/decel is fast enough it would bring the Z to a stop within the dead band.

THAT'S MY THEORY  

Perhaps when Mach3 was designed the deadband factor was not part of the design, and that's the reason no accel/decel was applied to THC moves.

Fast PID control effectively has accel/decel based on error. Smaller error, then slower correction speed, bigger error, faster correction speed.

Keith.

29

General Mach Discussion / Re: Physical buttons for plasma

« on: January 27, 2016, 12:43:51 AM »

Thanks Terry,

some time ago I tried using lower amps on Finecut nozzles and the cut quality was quite bad. Maybe that was an example of what you are telling me.

Keith.

30

General Mach Discussion / Re: Physical buttons for plasma

« on: January 26, 2016, 07:32:37 PM »

Rob,

I like the concept but have no idea if it's feasible. I haven't had a great deal to do with macropumps and don't know if there is any reason it won't work. But like I said I like your way of thinking, and I'm going to keep that idea in mind.

Initially I was thinking, "Ah but my THC will run at 32 times/sec", then realised that won't matter. If the THC UP or down signal is still there after 1/10th sec, then give it some help.

I hope it works  

Ah, just had a thought of a potential spanner in the works is when it stops at the higher speed. Let's say the macropump bumps the speed up then the SET VOLTS is reached, so the THC UP/DOWN signal is removed. Mach3 now will stop the Z without any deceleration, possibly causing the stepper to slip and lose it's holding torque and maybe stall. Worse case is it will stall and won't drive properly, or even when going down will keep going into the workpeice. Best case is you just lose position but the stepper keeps on doing corrections.

So this lack of acceleration may cut both ways. It limits your max instantaneous speed PLUS it MAY limit your max instantaneous stopping speed.

Something to keep in mind.

Keith.