Re: emc for wire edm control

[Michael Coffey <mdynac-at-prodigy.net>]

Ray Henry wrote:
> 
> Marcel
> 
> I have done a bit of work here and with Roland Friestad planning for such a 
> retrofit.  He has a two axis Agie wire EDM that is a few years beyond factory 
> service.
> 
> We had planned to use an analog signal for wire current but your approach 
> also sounds interesting.  This could simply be a voltage up signal 
> optocoupled to a parport pin and read by tkio.
> 
> One way to achieve the reverse path is to simply record the positions of each 
> axis for each motion loop.  This is how we ran the first backplotter.  The 
> second plotter does the math to make a vector from a whole series of points.  
> 
> With a file like this, when the parport pin goes low/high the grapical 
> interface could abort the running program, switch to mdi mode, and issues 
> each point back in the recorded position file as a g0.  Repeat this until the 
> pin clears.  Once cleared, we could restart the cut at the activeline when 
> the short happened unless we crossed position into a previous block of code.  
> If that happened we would need to decrement the activeline by 1 and restart 
> there.  
> 
> Cutter comp may cause a few problems but a few tests with the backplotter 
> should show a good approach here as well.
> 
> Ray
> 
> 
> On Wednesday 12 March 2003 12:18 pm, Marcel wrote:
> 
>>Hi
>>I want to know if its possible to change emc to control a two axis wire edm
>>machine. A wire edm machine need to be able to go back when the cutting
>>voltage is low (shorted) and only start to go back to the cutting direction
>>when voltage is high Regards
>>Marcel Gombault
>>
>>This email was scanned by the ICL anti-virus solution.
> 
> 
> 
Not all Wire EDM's "back up" during a shorted condition.
For example, most Japax wires go into feedhold during short,
and then continues along the contour after the short is cleared,
usually by flushing,
Sensing the voltage at the gap is the best way to achieve this.
A simple, yet precision comparator/opto circuit works nicely here.
Setting the circuit to output at, say 20 gap volts, is a good starting 
point. Then tweak it for best performance...
In my opinion I would get the machine up and burning using this 
approach, then delve into the more complex task of actually making the 
machine backup in a shorted condition.


I am currently working on a retrofit for wire/sinking/hole popping EDM's
Both servos and steppers.....

I have several old 2-axis "blue" Andrew 330's and 630's with servos, 
these macines do backup during short, a DEC PDP8\a is the heart of the 
axis motion on this beauty.
Does anyone know how to dis-assemble pdp8\a a code???

and an old Japax 4-axis machine with steppers, this machine feedholds 
during short

Hope this helps....
Michael