Mesa 7i96S + THCAD-2 for slow stand-off control (laser cleaning, auto air paint)

Hi all,I’m building a large vertical machine for laser cleaning and automated spray painting of heavy equipment (excavators, cranes, large fabricated parts and enclosures).Motion concept is a raster-based process:

• Z axis performs the working stroke (up/down) where laser cleaning or spray painting is applied
• Y axis is used only for slow stand-off distance control (surface following)
• X axis is used only between strokes for step-over / overlap indexing, then the next Z stroke starts
  
  For painting, we use automatic air spray guns (not airless / not AAA), since painting is done in a general workshop area without a dedicated spray booth. Typical overlap is around 60–70% between strokes.Current and planned hardware:
  • Mesa 7i96S (Ethernet, step/dir drives)
  • THCAD-2 for isolated analog-to-frequency input
  • Keyence distance sensor (starting with IL-1000, possibly upgrading to LK-G3000 series later)
  • Current: manual air spray gun 
  • Planned: automatic air spray gun 
  • Typical speeds:
    • Z working stroke: ~15–40 mm/s
    • X step-over between strokes: index only (no distance control)
    • Y axis: slow stand-off correction only
      
      Environment is electrically noisy (industrial equipment, welding, laser), so isolation is important.My questions:
      1. For this type of slow stand-off control on Y, is using THCAD-2 into the 7i96S encoder input a reasonable approach (non-plasma use)?
      2. If I upgrade to a faster sensor (LK-G3000), does THCAD-2 become a bottleneck for meaningful improvement?
      3. If I want proper fast isolated analog input, which Mesa hardware would you recommend to add ADC capability to a 7i96S-based system?
      4. Any practical tips for filtering, deadband, and loop rates for a ~10 Hz sensor like the IL-1000 in this application?
         
         Thanks in advance for any advice.

All that seems easy enough and Mesa combo should be more than enough fast for everything you mentioned.
1. Yes
2. No, unless you need something extremely fast, 1000Hz is normal servo rate, and even that can be pushed further
3. should all be doable easily, and 10Hz is very slow
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In general, plasma is the biggest offender regarding EMI noise, so you should be perfectly fine, granted the wiring and grounding and shielding is done correctly.
Regarding XYZ, it will be much easier to do a normal CNC machine setup, everything else can be set in gcode or some automated VCP panel to make use much easier and requires one time setups.
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I have been tasked with such painting automation about 15 years ago but the financing failed, still had some time to do some thinking about implementation, hence i might be a bit fuzzy on details.
Go for it, that would be my personal advice.

Thanks for the feedback — appreciated.

To clarify, my primary focus right now is using the Keyence IL-1000 for slow stand-off correction. Based on the discussion, I agree that THCAD-2 into a 7i96S encoder input should be sufficient in terms of raw speed and isolation for this use case.

My main concern is less about servo-thread rate and more about effective sensor update rate, frequency-to-velocity measurement noise, and required filtering/deadband for stable Y correction in a noisy industrial environment.

I’ve contacted Mesa support regarding isolated analog input options to complement a 7i96S-based system, but haven’t received a response yet. At the moment, many Mesa ADC-related boards appear to be out of stock in the US, and I’m considering purchasing from Europe. However, I’m a bit concerned about committing to hardware if Mesa is planning to release newer or replacement analog/ADC solutions in the near future.

If you (or others) have practical recommendations for current Mesa ADC hardware that works well with 7i96S, or insight into Mesa’s roadmap for analog input, I’d really appreciate hearing them.

LK-G3000 is only a possible future upgrade — the current design focus is on making IL-1000 work robustly and predictably.

The THCAD2 should be back in stock in the US by the end of the week.

Our other analog input card (the 7I87 6 channel +- 10V card) will still be about 4 weeks
but you don't need 6 channels...

For the THCAD2, the update rate is the servo thread rate (giving a loop bandwidth
of about 300 Hz at ~10 bit resolution) You can get better resolution by low pass
filtering (in hal) the frequency signal at the expense of loop bandwidth of course.

 If your height sensor only has 10 Hz bandwidth, you could easily increase the resolution
(to 12 bits or so) by this filtering since it will not affect system loop bandwidth significantly.

Thanks Peter — that’s very helpful.

That aligns well with my use case. Since the IL-1000 is only ~10 Hz bandwidth and Y motion is intentionally slow, trading loop bandwidth for higher effective resolution via low-pass filtering sounds ideal for stable stand-off control.

Given that, THCAD-2 looks like the right solution for the current phase, especially with it coming back in stock shortly.

For any future higher-speed sensor upgrades, I’ll revisit true ADC options like the 7i87 if needed — but for now THCAD-2 + filtering seems well matched to the application.

In addition, I will need extra isolated digital I/O for valves, interlocks, and machine signals. I was looking at the 7I84U isolated remote field I/O card (sourcing/sinking outputs), but it currently shows as out of stock. My preference is to stay within the Mesa ecosystem rather than using generic BOBs, to keep things robust and well-supported in an electrically noisy environment.

If you have any guidance on availability of the 7I84U, or alternative Mesa smart-serial I/O options that integrate well with 7i96S for isolated field I/O, I’d really appreciate your recommendation.

Thanks again for the detailed clarification.

Thanks Peter — one additional note: I also see that 7i96S and 7I84U are currently showing as out of stock on the Mesa store.

My preference is to stay fully within the Mesa ecosystem (rather than using generic BOBs), so if there are any expected restock timelines for 7i96S and 7I84U, or recommended current-production alternatives that keep a similar architecture, that would be very helpful for planning.

I can wait a bit if needed, but I’d like to avoid purchasing from Europe if these boards are expected to be restocked or revised in the near term.