Re: [CAD_CAM_EDM_DRO] Problem with Lindsay/Duncan DRO 5.1 program and IRQ interface

John A. McFadden wrote:

>Forewarning: I'm not an electrical engineer (I'm a chem eng), so I might get
>some of the terms wrong, please bear with me on this.
>
>
>
>I'm using the DRO program and interface designed by Steve Lindsay and
>updated by Robert Duncan, version 5.1 with the updated integrated circuit
>with IRQ schematic (with one change, I used two 7486 chips (quad exclusive
>or), in place of the two 4077 chips (quad exclusive nor), as I had them
>on-hand, the wiring of the board was corrected to accommodate the change, as
>functionally they should be identical in this application but the pinouts
>are slightly different, according to my dad, an electrical engineer) and I'm
>having a problem with the IRQ portion of the interface. The program is
>running on a Pentium 133 laptop with 48 megs of ram using the IRQ mode of
>operation, step size is 0.00039xxx"/step on X and Y, and 0.00069xxx"/step on
>the Z (Encoder Tech 25cpmm linear strips on X and Y, US Digital 360cpi
>linear strip on Z).
>
>
>
>When two encoders transition simultaneously (for example, moving both X and
>Y at the same time at a rapid pace), eventually the two axis will have a
>transition extremely close together and the IRQ does not have time to reset
>after the transition from one axis before the transition from the other axis
>occurs. Thus, the IRQ 'misses' a transition, while the raw data catches it
>and the program counts this as an error (as it saw a data transition, but no
>IRQ transition) and loses the 'missed' movement.
>
>

Well, this is obviously a total design flaw of the software!

>
>
>This is giving me fits as my Enco Mill/Drill has enough vibration to trigger
>transitions in the Z or Y axis (yes, I get lazy and don't always lock the
>non-moving axis as I should, as I mostly use it to mill out areas wider than
>the diameter of the end mill) when I am milling in the X direction, thus
>losing count on one of the axis and screwing the whole thing up.
>
>
>
>If I turn off the IRQ mode, I can move all three axis (with my dad lending a
>hand to move the 3rd one) as fast as I can spin the handles with no errors,
>but I'd prefer the certainty of the IRQ interface rather than relying on raw
>computing power to not miss a transition.
>
>

What is the purpose of the IRQ mode? it seems like it reduces the
reliability of
the program. Still, I prefer to use dedicated hardware for this. My
hardware
can count up to 300,000 encoder counts per second on each axis,
simultaneously.
If that isn't fast enough, the digital filtering can be set for a
shorter interval,
and easily go to 1 million counts/second. With dedicated hardware, you
don't
have to worry about a CPU having to service a memory refresh or timer
interrupt, it is always doing the exact task it is designed for, and
never being
'borrowed' for any other task.

The US Digital LS7166 chip is pretty similar to what I designed in my
projects,
and they are only about $11, I think. The interface to read them out is
very
simple, and 3 of them could be connected to a parallel port with minimal
interfacing circuits. All you'd need are one decoder to select each chip
separately.

Jon

>
>
>Technical diagram and explanation:
>
>If I'm a little unclear, download this interface schematic:
>http://ns1.dicomm.net/~axtein/dro/irq.zip and examine the file irq.jpg
>contained within: if pin 10 of U4 and pin 10 of U3 transition simultaneously
>(as would happen if moving the X or Y axis while also moving the Z or A
>axis)(not exactly simultaneously, just very, very close together with
>regards to time), pin 11 of U3 will not transition as required and the
>system will have an error. This also happens if pin 3 of U3 and pin 4 of U3
>transition simultaneously, pin 10 of U3 will miss, or if pin 3 of U4 and pin
>4 of U4 transition simultaneously pin 10 of U4 will miss, so all three gates
>would need to be replaced.
>
>
>
>So, in conclusion, I'll get to my questions:
>
>Have other users of the IRQ interface mode of the DRO 5.1 software noticed
>errors when two axis transition at the same time? Or is this a problem of
>my own doing, due to the substituion of the 7486 chips for the 4077 chips?
>
>
>
>Are there any logic chips (or other solutions) that can replace the
>4077/7486 chips (rewiring the board would be acceptable, this is assuming
>that the 4077 chips would have the same problem as my 7486 chips) that would
>fix the problem of the missed transitions?
>
>
>
>Thanks,
>
>John
>
>
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