late in 2005 successful wire edm was accomplished by 'mdynac' 
 photo at http://timeguy.com/cradek-files/emc/edm/MVC-028S.JPG
 This used the idea from RayH to slow down the veloicty based on feedback of gap voltage.
 It used Hal components wired into the feedrate override.
 

Electrical Discharge Machining aka EDM

Ray's suggestion:

We will need to build some sort of specialized interpreter script to handle reversing. This script should run whenever a HAL_edm pin is true. This could be written in Tcl for proof of ability. Once the ability has been proven, it should be rewritten in a compilable language for speed and operation across the several guis. Dave thinks that with minimal changing arcs can be handled as easily as line segments.

The edm functions could be built into the existing emc2 interpreter if it were made to save blocks of gcode rather than simply reading, making canonical commands, and discarding.

The following pins and parameters are just suggested. Please edit these as you see fit.

• Pins
  • EDM Current (integer input to hal)
  • EDM Feed (integer output for feedrate override)
  • EDM Reverse (bit output to reverse motion)

• Parameters
  • EDM Type (integer 1=wire 2=sinker 3=hole drill ...
  • EDM Reverse setting (integer)

.

2006 09 13 a discussion on emc irc suggests that a different tack is needed for edm, and that using HAL directly is plausible. This means emc's trajectory planner wont be used intially. Tho a lot of the emc framework is wanted and needed, these tests will be a bit outside. The AXIS front end for EMC can display position for the Hal governed motion.

Dave Engvall has a way to send streams of positions to usrmot. He use a component from John Kasunich 'hal-streamer'. While emc2.0.3 is running, he opens a terminal and runs usrmot, there, he can manually or programmaticly ask for positions as triplets (thinking inside the xyz box for now ) ie: 25.4, 12.7, 50.8 and can change the request at will. you can try this yourself! now if we can get a program to determine where the electrode ought to be right now, we'd have a big part of the edm control done! This is not gcode, just a stream of positions from an external program.

Peter Gruendeman is working on a machine tool and generator.

• 2006 03 02  John Kasunich wrote about thoughts he's had on realtime dynamic feedrate.
  "The second issue would be REALTIME control of scale.  That would
  not use NML feedrate override messages (too slow), instead it would
  be a HAL pin connected directly to the realtime motion controller
  that would modify the feedrate on a servo-cycle by servo-cycle basis."
  thanks John
  

• 2006 03 03  Alex Joni has agreed to create a new hal pin to help in EDM
  reported by MAC
  > I contacted Alex Joni and he is going to set up a hal pin to control 
  > feedrate override. So i should be able to apply a varying voltage to 
  > the Motenc adc input and get  an output to be used by emc2.
  "
  we can test with a pot and a battery asap :-)
  no need to wait for a whole edm machine. kewl
  Thanks Mac & Alex
  

• 2006 03 10
  Ben Fleming & Michael Erbe have teamed up to build a new EDM power supply.
  They may help the emc group in the EDM effort by letting us use thier generator.
  Ben & Mike have developed a new generator and will show it off at the 2006 fest.
  http://www.lindsaybks.com/bks9/edm/index.html
  

• here's C. Scott Ananian's Garden of EDM power supply pcb
  it's in PCB format ( a free pcb layout tool for Linux )
  surely would benefit from someone who knew electronics rather than plumbing :-)
  (requires oscillator and is a generator, not a servo sense circuit )
  This just the pcb, the design is in xcircuit format.
  The design is available at Scott's site.
  

            upload:goe-scottsvrsn23q

CNC code fiddling

• Jon Elson wrote some excellent tools,
  available at 

  http://pico-systems.com/gcode.html

• found a lot of code for emc by some guys writing in ruby
  these people put a lot of work into these routines, thanks!
  look at  

  http://xdobs.com/cnc/runing_program.html

CNC EDM for EDM

in general, the class of controller suited to EDM are 'gap-width controllers'.
that is the name to google for, 
it is a class of control, 
used by other disciplines besides EDM.

here's a 10 page pdf explaining why mill controls dont work for edm, and what does

upload:edm-cnc-paper_nc.pdf

• excerpts:
  
  In EDM the feedrate can not be defined by the user. The electrode speed is
  determined by the process. ...
  NC-concepts based on a constant velocity movement along a wide part of the 
  course cannot be used [6]
  ...
  The target feedrate (Vb) is computed by the gap-width controller based on an actual
  evaluation of the ED-process. Vb is valiud only for one NC sample-time (T).
  Next step in calculation is the check of the target feed rate.
  In caase of exceeding the maximal admitted acceleration a correction of the feedrate
  is made to avoid a deviation of the target course. Based on this proven feedrate (V'b)
  the increment along the course (delta s ) is calculated and the interpolation can
  generate a new target position (Xt, Yt, Zt) for the drives"
  

• <pre>

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