The Langlois stepper controller design does not really use the same step direction principle that the common drive does, it incorporates a 'ripple type counter' that is ran from a 555 settable pulse generator.
the direction is detected by sampling the charged capacitor voltage, then counts either up or down, depending on the direction required.
Max.

So your saying my Pac/Sci driver won't work? I'll have to go out in the barn and look for them, all that stuff is in storage. Well I do have all the parts to build the Langlois version. Bought them years ago, as that was the machine I started to build.

 

So your saying my Pac/Sci driver won't work? I'll have to go out in the barn and look for them, all that stuff is in storage. Well I do have all the parts to build the Langlois version. Bought them years ago, as that was the machine I started to build.

I don't think that's what he's saying... I think he means only that the Langlois version had a different approach to controlling the thing. My personal opinion is that Langlois' version is simpler... but maybe all those gates and stuff could be simplified by using a simple MCU... question, do you own, or have access to, a device programmer?

 

You most likely could incorporate a step/dir controller, just that you need some logic before it to provide the step rate and do the reversal dependent on the capacitor charge or electrode voltage.
Max.

 

You most likely could incorporate a step/dir controller, just that you need some logic before it to provide the step rate and do the reversal dependent on the capacitor charge or electrode voltage.
Max.

I agree, and by using an MCU he could have far greater options and flexibility with a much simpler circuit. The key question is if he has access to a device programmer. Because if he does, I'd be more than happy to help him with the programming needed.

 

I thought it worked like this:
Where the working voltage basically tells you how far the tool is from the part.
My concern is what the stepper does with all the "extra" pulses before it has time to move.
Sorry it's sideways.

 

Ron, a stepper does not accumulate steps in a buffer, each step has to be completed before the next is generated by the driver, or otherwise the motor will stall.
Steps are usually generated using a square wave, maybe we could just wait until the falling edge of that wave to re-analize the comparator window and then generating either the forward or backward step as needed, or simply not generate any steps.

 

The gap voltage (should) spend most of its time in the 'dead zone' no movement of the ram control comparator. This is after the initial spark of the burn, when it first gets close enough to spark. It will only move forward when the spark can't establish. After it is close enough to spark, the next pulse rise time is much faster than the gap control can react, so instead of moving down (it is just a vertical move) the new pulse goes into the dead/working voltage zone again, with no movement needed. The window comparator and stepper drive work together, the comparator giving feed back to the driver and ram. No other logic needed in this part of the circuit.

What you are saying
is that the only time you give a move in command is when there is no arc? Much Simpler. But then what is the window for?????

 

Just to make sure I'm not misinterpreting things.
Things should work like this:

Check voltage using two comparators, this should give us two binary numbers one for voltage too high (tool too far) and another for voltage too low (tool too close), lets name those variables vth and vtl, and they can have a value of only 0 and 1. And by definition they cannot be 1 at the same time.

start:
check comparators, and load values of vth and vtl
  If vth = 1 then step_forward : skip to delay_loop
  If vtl = 1 then step_backward : skip to delay_loop
  /* if both vth and vtl were 0, then nothing will be done */
delay_loop:
  wait a minimum of X milliseconds
GOTO start

 

That's what I thought too. But then I saw this:

It will only move forward when the spark can't establish

 

But then I saw page 140.
https://books.google.com/books?id=F...e&q=edm spark gap voltage measurement&f=false

Edit:
Repasted link

 

The link does not work for me.
Here is a page with video/audio also.
http://www.engineersedge.com/edm.shtml
Max.

 

I reposted it. Think it works now.

 

Ron, if you go back to post # 118 and look at file "edm 073", near the bottom right side of the page it shows a drawing of the window comparator voltages and what happens. Remember there is a 5v null in the window, this is what happens -

1. 95V to 35V - electrode moves closer to work.

2. Between 35V to 30V - no movement, null point of window.

3. 29V to 0V - short or too close, electrode backs off from work. The 29V is a guess, might be little more or little less depends on sensitivity of comparator.

Once the distance is established to spark, as each new spark starts the voltage drops so fast to the window or working voltage, the stepper diver doesn't have time to respond before it is in the 'null' voltage again.

The page from the Jameson book means that it advances only when the gap is too big to let a spark establish, whether it is just beginning to burn or it has removed so much metal the spark no longer will happen.

 

You most likely could incorporate a step/dir controller, just that you need some logic before it to provide the step rate and do the reversal dependent on the capacitor charge or electrode voltage.
Max.

I thought about this after posting, and did have this worked out years ago, mind is rusty on this project.

There are tree inputs to the driver modules I have, speed - direction - enable.

Speed is from a simple 555 circuit.
Direction is either a 1 or 0, a + V or 0 volt.
Enable is tide to volt value needed to be "able"

1. The comparator outputs control the input pins of a 4066 switch chip.

2. When the need from the comparator is to go down the 4066 activates two of the four switches, giving the speed signal pulses to the drive speed input and +V to the direction input.

3. No 4066 switches activated when comparator in the 'window'.

4. When the need to retract is signaled from the comparator, two of the 4066 switches are turned on, giving the speed pulse signal and a 0 V to the drive module.

I knew I figured it out years ago, threw me when I thought you meant it wouldn't work

 

Ron, if you go back to post # 118 and look at file "edm 073", near the bottom right side of the page it shows a drawing of the window comparator voltages and what happens. Remember there is a 5v null in the window, this is what happens -

1. 95V to 35V - electrode moves closer to work.

2. Between 35V to 30V - no movement, null point of window.

3. 29V to 0V - short or too close, electrode backs off from work. The 29V is a guess, might be little more or little less depends on sensitivity of comparator.

Once the distance is established to spark, as each new spark starts the voltage drops so fast to the window or working voltage, the stepper diver doesn't have time to respond before it is in the 'null' voltage again.

The page from the Jameson book means that it advances only when the gap is too big to let a spark establish, whether it is just beginning to burn or it has removed so much metal the spark no longer will happen.

Yes, that's how I thought it worked. The problem, I think, is the several move in or move out pulses that will occur before the motor can move.(Post 125) I don't think the motor control will like this. I can make it so it only sends one or asserts disable and waits until the motor has had time to move before it checks the window again, but to do that I need some idea of how long to wait. This is probably related to maximum step rate of the motor, controller. I can guess, but if we know how long it takes the motor to do a step it would be a better guess. A better solution might be to stop sparking until the motor has had time to move just in case there are some vibrations in the mechanics that could move the probe around during the pulse from the motor moving.
The plan is to make the window 5 volts wide and the center movable from a low of 22 and a high of 50 volts.

 

Yes, that's how I thought it worked. The problem, I think, is the several move in or move out pulses that will occur before the motor can move.(Post 125) I don't think the motor control will like this. I can make it so it only sends one or asserts disable and waits until the motor has had time to move before it checks the window again, but to do that I need some idea of how long to wait. This is probably related to maximum step rate of the motor, controller. I can guess, but if we know how long it takes the motor to do a step it would be a better guess. A better solution might be to stop sparking until the motor has had time to move just in case there are some vibrations in the mechanics that could move the probe around during the pulse from the motor moving.
The plan is to make the window 5 volts wide and the center movable from a low of 22 and a high of 50 volts.

From experience alone, I'd say a maximum of 300 steps per second when one's expecting a sudden change in direction is a reasonable step frequency

 

So maybe I'll put in 5 ms. for now at least.

 

So maybe I'll put in 5 ms. for now at least.

Just to clarify, that number is adequate when 400 steps per revolution are being used in the motor. And it also depends on the load, but in this application that should amount to just some friction and a little tiny bit of inertia.

 

Maybe I better make it 10 ms. Better safe than sorry.

 

Not to be hard headed with this, but you guy's are still over thinking the motor part of it. A little 'vibration' of the electrode is a good thing in this, it helps to get the debris out of the gap. The time spent at one point of depth is fairly long in the scheme of this. The metal removal rate in edm is more like scraping or sanding a surface than drilling a hole. The big idea behind edm is the ability to machine things that can't be done easily any other way. Of all the machine shop procedures it is one of the slowest and most expensive due to the time to remove the metal. I'll try and see if there are any Youtube videos of homemade edm's burning and post a link if one is found. There were some a few years ago.

The most popular of the homemade machines doesn't even use a stepper but a Maxon gearmotor with a 80RPM output. And they have been made worldwide and according to the makers, working.

Cmartinez, you mentioned programing and using a micro for this. I have no experience with a micro, but with the talk of others trying to build DIY edm machines that have tried using them, it's not the programing that is the bottle neck, it's RF and electrical noise that edm makes that is the problem. Even using optocoupling doesn't get around it. But using the old TTL CD4xxx logic doesn't seem to have as much problem.