Anyone know where to find in depth technical details of DRO scales?

Or you could put the tablit in a ziplock bage. Just a thought.
 
ScrapMetal said:
What I am looking for is the method in which the reader heads return position information to the main unit. I assume that different brands use different (maybe proprietary?) protocols but I need a place to start.

About the only information I've been able to find so far is that one "standard" is to use a double sine wave where the signals are 90 degrees out of phase with each other. That's great and all but I still haven't read any where just how that is used to relay position. Phase change? Amplitude? Frequency? I don't know.

What I have in mind with this is to see if I can use a micro-controller (that I've been learning/experimenting with) to create an inexpensive DRO system for a lathe that is fully functional and has "professional" quality accuracy. Basically the next level up (or a couple of levels :biggrin:) from using the iGaging stuff. If I can make a unit that can be used with a number of different manufacturer's scales it would just be that much better.

Now, I could just hook up the scales I have to the oscilloscope, and I will, but that could prove to be a bit tedious and only give me limited information for one brand. If I can speed up the information gathering it will be a "good thing". :)

All tips and info will be much appreciated.

Thanks,

-Ron
Click to expand...

A linear scale works just like an incremental rotary encoder (that you'll find a lot of info about) with decoding done by a relatively simple digital circuit.

Let's talk about a digital scale first... Usually scales use two signals in quadrature (90 degrees apart in phase) to indicate movement. Let's call the two signals A and B. Every time a transition occurs on either A or B, that increments or decrements a count value by one. If the A track leads the B track, that's one direction. If B leads A, that's the other direction. With a 4X quadrature detector, you can get resolution 4 times (4X) the number of pulses per unit length. Basically, they work like this: if a transition is seen on one track, the level of the other track determines whether to count up or down.

So, what circuit does this? In its simplest form, it's just A XOR B. But that doesn't give you direction, just relative movement with the count going in the same direction regardless of direction. Adding one more XOR gate and four flip flops and a clock source, along with a counter gives you position. The c ount value just needs to be scaled into engineering units (inches, mm, etc). This is also readily done in a small microcontroller with an input capture feature (or maybe even just digital inputs)

So what I've described can measure relative distance. Some scales also have a third signal, the Z track which is used to reset the count for absolute position sensing.

Sinusoidal encoders are very similar in concept, except the fact that they are outputing analog signals (sine and cosine) allows for more than 4X resolution by a process called interpolation. Think of a digital encoder as described above where every zero crossing resynchronizes the interpolator (just like the 4X quadrature detector) to prevent cumulative error. You can use a circuit to square up the sine and cosine outputs and sinple feed them into the digital circuit described above.

OK, that's how typical higher end scales work.

Many Chinese scales use a serial output because the interpolation and quadrature detection happens in their circuitry and position is the output. They use a variety of protocols.

https://en.wikipedia.org/wiki/Linear_encoder


John
 
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kd4gij said:
Or you could put the tablit in a ziplock bage. Just a thought.
Click to expand...

That would help to keep the screen from getting oiled but it would bring it's own issues with it. Still wouldn't help much with the hot metal either.

Thanks.

-Ron


jgedde said:
A linear scale works just like an incremental rotary encoder (that you'll find a lot of info about) with decoding done by a relatively simple digital circuit.

Let's talk about a digital scale first... Usually scales use two signals in quadrature (90 degrees apart in phase) to indicate movement. Let's call the two signals A and B. Every time a transition occurs on either A or B, that increments or decrements a count value by one. If the A track leads the B track, that's one direction. If B leads A, that's the other direction. With a 4X quadrature detector, you can get resolution 4 times (4X) the number of pulses per unit length. Basically, they work like this: if a transition is seen on one track, the level of the other track determines whether to count up or down.

So, what circuit does this? In its simplest form, it's just A XOR B. But that doesn't give you direction, just relative movement with the count going in the same direction regardless of direction. Adding one more XOR gate and four flip flops and a clock source, along with a counter gives you position. The c ount value just needs to be scaled into engineering units (inches, mm, etc). This is also readily done in a small microcontroller with an input capture feature (or maybe even just digital inputs)

So what I've described can measure relative distance. Some scales also have a third signal, the Z track which is used to reset the count for absolute position sensing.

Sinusoidal encoders are very similar in concept, except the fact that they are outputing analog signals (sine and cosine) allows for more than 4X resolution by a process called interpolation. Think of a digital encoder as described above where every zero crossing resynchronizes the interpolator (just like the 4X quadrature detector) to prevent cumulative error. You can use a circuit to square up the sine and cosine outputs and sinple feed them into the digital circuit described above.

OK, that's how typical higher end scales work.

Many Chinese scales use a serial output because the interpolation and quadrature detection happens in their circuitry and position is the output. They use a variety of protocols.

https://en.wikipedia.org/wiki/Linear_encoder


John
Click to expand...

John, thanks much. Lots of good information and many things to consider.

-Ron
 
Not sure why you think a touch screen would fair that poorly in a shop environment. They are made of glass after all. Something like an iPad of course was not designed for an industrial environment, but a more robust touch screen device wouldn't look much different - it's a glass screen with a metal case. In fact with the right design for one of those after-market cases, I think a tablet would do fine. Sure the screen would get dirty, but glass is easy to clean. Also a good software design would have you touching only button areas and not readout numerals, so the end result would be no worse than greasy buttons on a conventional DRO.

ScrapMetal said:
That would help to keep the screen from getting oiled but it would bring it's own issues with it. Still wouldn't help much with the hot metal either.
Click to expand...
 
lens42 said:
Not sure why you think a touch screen would fair that poorly in a shop environment. They are made of glass after all. Something like an iPad of course was not designed for an industrial environment, but a more robust touch screen device wouldn't look much different - it's a glass screen with a metal case. In fact with the right design for one of those after-market cases, I think a tablet would do fine. Sure the screen would get dirty, but glass is easy to clean. Also a good software design would have you touching only button areas and not readout numerals, so the end result would be no worse than greasy buttons on a conventional DRO.

ScrapMetal said:
That would help to keep the screen from getting oiled but it would bring it's own issues with it. Still wouldn't help much with the hot metal either.
Click to expand...

I guess I'm just stuck in my ways. I just can't see subjecting a relatively expensive/delicate piece of computer gear to an environment it was not designed for. I know that they try and design tablets to take as much abuse as they resonably can for people who tend to drop them or throw them on the table (like my eldest daughter :rolleyes:) but they still aren't made for taking the constant heavy vibrations they may be subjected to if mounted to a lathe or mill. Touch screens on iPads etc. get scratched and hard to read just from their intended use that's why there is a market for screen protectors (which are clear mylar, plastic, or some such). Taking that same screen and subjecting it to swarf and metal filings just doesn't make sense to me. Cleaning up the oil on the screen may be the least of the worries as these devices aren't generally made to be water/fluid resistant either. Now granted, even the industrial stuff might not be "water proof" but they are still designed in such a way that if a little oil or such gets in the case they will still function. I really doubt that to be the case with an iPhone, iPad, Android device, etc.

Why bother subjecting your expensive personal electronics to destructive environments that they were not designed for? Especially when the ones designed for that purpose are generally even cheaper than said device?

People can do what they want but it just doesn't make a lot of sense to me.

JMHO as always :biggrin:

-Ron
Click to expand...
 
You can get 10" taplits for under $ 100.00 now days thus his choice to go that rout. But hay it is your shop and your money so what ever soots you. Just anouther option for some people not so much for outhers.
 
ScrapMetal said:
lens42 said:
Not sure why you think a touch screen would fair that poorly in a shop environment. They are made of glass after all. Something like an iPad of course was not designed for an industrial environment, but a more robust touch screen device wouldn't look much different - it's a glass screen with a metal case. In fact with the right design for one of those after-market cases, I think a tablet would do fine. Sure the screen would get dirty, but glass is easy to clean. Also a good software design would have you touching only button areas and not readout numerals, so the end result would be no worse than greasy buttons on a conventional DRO.



I guess I'm just stuck in my ways. I just can't see subjecting a relatively expensive/delicate piece of computer gear to an environment it was not designed for. I know that they try and design tablets to take as much abuse as they resonably can for people who tend to drop them or throw them on the table (like my eldest daughter :rolleyes:) but they still aren't made for taking the constant heavy vibrations they may be subjected to if mounted to a lathe or mill. Touch screens on iPads etc. get scratched and hard to read just from their intended use that's why there is a market for screen protectors (which are clear mylar, plastic, or some such). Taking that same screen and subjecting it to swarf and metal filings just doesn't make sense to me. Cleaning up the oil on the screen may be the least of the worries as these devices aren't generally made to be water/fluid resistant either. Now granted, even the industrial stuff might not be "water proof" but they are still designed in such a way that if a little oil or such gets in the case they will still function. I really doubt that to be the case with an iPhone, iPad, Android device, etc.

Why bother subjecting your expensive personal electronics to destructive environments that they were not designed for? Especially when the ones designed for that purpose are generally even cheaper than said device?

People can do what they want but it just doesn't make a lot of sense to me.

JMHO as always :biggrin:

-Ron
Click to expand...

Ron,
You'd be surprised what a good quality protective case can do for you :)
Take a look at this post: http://www.yuriystoys.com/2013/01/gumdrop-case-to-make-my-tablet-garage.html
That tabled has been in my garage for close to 6 months now (being constantly moved between the mill and the lathe) and it's holding up like a charm (it's pretty much dust proof and comes with a built-in screen protector).

There is always a chance of dropping it screen-down, of course, but that is "up to the pilot" to be a bit more careful.

Thank you
Yuriy

P.S. My other tablet (Nook Color) gets subjected to a much more harsh environment on long road trips by my 6 year old daughter :) (drool, milk, chicken nugget grease, you name it) and is still alive after 3 years of that...
Click to expand...
 
Thanks Yuri. I've been on your site for a couple of quick "look arounds" and I'm very impressed with all the work you've done. I plan to go back and spend a lot more time there as you've provided a lot of information that I may find useful to my own project. Thank you very much for that.

My issues with the iPads, etc. probably come down to the fact that I'm morphing in to an "old fogey" (or setting the standard, not sure which :biggrin:). It seems everyone wants to do "everything" with their smart phone or iPad, etc. but I really don't see the point even though I respect being able to do it. I'm more of an "the right tool for job" kind of guy and it just seems that if you are dedicating a device for a particular job it's best to have one that is designed for doing that job.

If, say you're are using your iPhone for everything, internet access, DRO, phone, etc. and it falls out while you are mountain biking and smashes on the rocks (if it doesn't get destroyed while using in a shop). You are absolutely dead in the water, can't do work (DRO is out), can't get online, or call for assistance, etc. etc. Granted, a dedicated DRO can take a dump as well but at least I can get online and order a new one or call the local distributor to see if they have one in stock. ;)

I see the allure of creating this as I went to college for electronics engineering and spent the last 30 years as a programmer. I love to play with stuff. For a dedicated tool in the shop for the average guy? Not really, they just want to push the button and get an answer not tweak the code for their own wants/needs. It's almost a waste to see computing devices like these dedicated to mundane shop functions. It seems to me like taking a $500 computer and programming it to be a $20 calculator.

Still, thanks again for your site. It is much appreciated.

The old fogey,

-Ron
 
kd4gij said:
Ron

Yuriy does have a stand alone dro that he built you can find it here. It might help in your project.
http://www.yuriystoys.com/2012/02/diy-digital-readout-project-update.html
Click to expand...

Yep :)
Just got a new batch of boards as well.
I've built 5 Android-based units so far (not counting prototypes) and about two dozen of the simple "3 readouts with 6 buttons" for friends (and friends of the friends) :)

Here is the supreme irony:
Android version's total cost is $20 + tablet ($4.50 for MSP430 Launchpad, $11 for the BT module and the change for the connectors). With a cheap tablet (assuming you don't already have an old phone laying around) it's $120-$150 tops and takes about an hour to build.
Standalone version's cost is over $150 (3 LED driver chips alone are $50, + $35 for the Arduino + $77 for the PCB) and I can put one together in about 6 hours, including the machining of the case, etc.

Thank you
Yuriy
 
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