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Laser Interferometry for machine refurbish

drcoelho

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Feb 19, 2017
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Los Altos
Anyone using Laser Interferometry for evaluating/refurbishing machines, e.g. lathes, mills, etc? If so, what is your experience and can this technique be used for all measurements scenarios?
 
perhaps no one is willing to write a very long essay discussing all measurement scenarios, since it would be quite a waste of time...
 
I think your question is just worded out of line with how most of the industry approaches use of laser interferometers. They are used as part the calibration process to establish error comp tables. They are are able to examine the dynamics of both the mechanics and control combined.

So if your question is about if anyone is doing laser machine calibration, I bet some others can chime in on what they are doing, when, and why.

Lasers in the common configuration don't seem to be commonly used in refurbishing. They certainly can tell you what is out of alignment, but they aren't that efficient at telling you why and how to fix it. A straight edge is pretty good for that. Lasers systems are pretty expensive unless you have a lot of knowledge to assemble an interferometer and process data from it yourself.
 
perhaps no one is willing to write a very long essay discussing all measurement scenarios, since it would be quite a waste of time...

Ha, yeah, the OP's question is a bit like asking is anyone using tools with digital encoders to measure parts?
 
I have a series of machines that I'll be refurbishing (both Lathes and Mills) and I was thinking (ignoring the cost issue) that a product such as the Renishaw XK10 might be an interesting way of going to get very accurate measurements and for ease of such measurements. I would be looking to make all the usual measurements to calibrate the machines, e.g. ways straight and flat, parallel ways actually parallel, spindle allignment, etc....in reading the brochure for the XK10 it seems to be a device setup specifically for this kind of work.
 
I think you way underestimate the price tag of this playground.

In college I built an interferometer do 3d shape measurement of a 20mmx20mm moving stage with around 1nm resolution in Z. I think it had about $10K of parts in it and probably 1000 hours of my own time. So you can do it cheapish. Nice user interface to quickly take measurements...hell no. A lot of the money in these things is in the software.

Any idea what the Renishaw XK10 runs that he OP is looking at.

If you find the right bare sensor setup for general automation purposes, you can assembly your own though. I'll have to think about who makes a setup that functionally does what you are looking for.

For example, these optical mics are pretty good for looking at run out in the sub tenths range and can be had used for a few thousand $: High-speed, High-accuracy Digital Micrometer - LS-7000 series | KEYENCE America
 
I occasionally get an idea to look for one on ebay or wherever. A used renishaw set usually runs in the 5-10k (£) range depending on how old/which model. Keeping it in calibration would about double that over a 5 year period of ownership I guess.

I have only ever seen an interferometer used to calibrate CMMs and larger mills. The guys that come to do our CMM use one of the more recent renishaw ones and do pitch, squareness and parallelism with it. Small machines more commonly a ballbar is used for geometry/mechanical and length standards for pitch.
 
Some are talking laser 1D measurement which are like a nice DTI and others laser alignment systems that give much more information.
A complete setup for machine ways would run about $50,000 with all the add ones.
Then in use you have to compensate for air temp and humidity which plays havoc.
The HP and Rein systems are the cat's ass by far but very hard to use and setup. SOP in the larger price CMM world.
A simple LVDT done right will run circles around a laser displacement probe. Rayleigh limit.
Bob
 
$50K is actually a bit less than I would have guessed for a full blown system capable of linear measurement, straightness, and squareness. I was thinking about 2-3x that.

There are definitely advantages and limitations to non contact measurements like lasers. Oil films are a real jerk with non contact measurements.

What does the Rayleigh Criterion have to do with linear type interferometer measurements? I thought Rayleigh had to do with angular resolution related to diffraction limits. In interferometry "Z" axis measurements are sub 1/2 wavelength when interpolating interference patterns. Accuracy can be influenced a lot by environment, but relative measurements can be very good.

This page is worth a read: Interferometry explained
 
Some are talking laser 1D measurement which are like a nice DTI and others laser alignment systems that give much more information.
A complete setup for machine ways would run about $50,000 with all the add ones.
Then in use you have to compensate for air temp and humidity which plays havoc.
The HP and Rein systems are the cat's ass by far but very hard to use and setup. SOP in the larger price CMM world.
A simple LVDT done right will run circles around a laser displacement probe. Rayleigh limit.
Bob

The Renishaw XK10 system seems based on the videos and other info I've looked at to be reasonably easy to setup....when you say "hard to use and setup" can you describe the issues in more detail? Also XK40 has temp/humidity sensors and counter measures integrated to help with this issue some...I'd also be doing this work in humidity/temp controlled environment.
 
Any of the metrology lasers will deal with temperature, humidity, and air pressure (in how these affect the laser beam). They typically also have a material sensor to measure the temperature of the thing you are measuring, so you can compensate that is you want.

BTW; air pressure is the thing that affects laser measurement the most.

Here is info on Keysight, formerly Agilent, formerly HP: they are quite expensive;
5530 Laser Calibration System | Keysight

Here is a link to one of Laser Sams pages (there are hundreds!);
Considerations in Evaluating Used or Rebuilt Hewlett Packard/Agilent/Keysight Metrology Lasers

Optodyne may be less money- not sure of the quality.;
CNC CMM Machine Tool Laser Calibration Interferometer
 
Some are talking laser 1D measurement which are like a nice DTI and others laser alignment systems that give much more information.
A complete setup for machine ways would run about $50,000 with all the add ones.
Then in use you have to compensate for air temp and humidity which plays havoc.
The HP and Rein systems are the cat's ass by far but very hard to use and setup. SOP in the larger price CMM world.
A simple LVDT done right will run circles around a laser displacement probe. Rayleigh limit.
Bob

Bob, you are correct about the pricing (confirmed with quote) :) BUT, these Renishaw XK10 devices do auto compensation for temp and humidity so that is less of an issue.
 
Some are talking laser 1D measurement which are like a nice DTI and others laser alignment systems that give much more information.
A complete setup for machine ways would run about $50,000 with all the add ones.
Then in use you have to compensate for air temp and humidity which plays havoc.
The HP and Rein systems are the cat's ass by far but very hard to use and setup. SOP in the larger price CMM world.
A simple LVDT done right will run circles around a laser displacement probe. Rayleigh limit.
Bob

So I'm researching the LVDT stuff, and my impression is that these are glorified (very accurate) indicator type devices....seems to me that one still has a problem in setting up jigs to hold these guys...am I missing something?
 
Mixing apples and oranges in some of the discussion here.
Laser displacement probes are basically optical indicators and laser OD scanners are also of this ilk.
Think a camera or line scan sensor looking at the beam, hence the optical limits.

Different animals than interferometer laser alignment systems.
It has been a very long time since I used a HP system, obviously the use of built in microprocessors makes then smarter and easier to use.
The machines I was calibrating at the time ran on a PDP-11 or Vax so obviously my information about ease of setup and use is much dated.
Bob
 
The Renishaw XK10 is a laser interferometry system, with all software included in a small handheld wireless computer. Out of the box it does straightness, squareness, flatness, level, parallelism, coaxiality and spindle direction with simple jig setup. Accuracy is on the order of 1 micrometer, which is close but a little less than LVDT.

P.S. I too worked on PDP-11s and Vax's :)
 








 
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