home made linear encoders??

[Mcgyver]

reading David's efforts on hooking up encoders got me thinking....do the electronic geniuses here think that a home made version of a Newall encoder is possible?

If you don't know what a Newall encoder is, check out http://www.newall.com/LEDs/operation.htm

They are a very neat linear encoder technolgoy, y are accurate to like 1 micron over a meter and have no moving parts.

Unlike glass scales, maybe, just maybe, that head with the coils could be a diy project - I don't know enough about electronics to know if thats nonsence or not, but if possible it would open up cheap dro and closed loop servo bases cnc systems for the home shop, which imo would be very cool.

what do you guys think - would it be feasible and you have ideas on how to build the encoder unit??

[topct]

Aren't these very expensive? There is a reason why. And does an HSM need this kind of accuracy?



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Gene

[IOWOLF]

If you can do it just as accurate and still be cheaper than a store bought DRO,Great, they are sure easy on the eyes.

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The tame Wolf !

[Leigh]

<font face="Verdana, Arial" size="2">Originally posted by Mcgyver:
reading David's efforts on hooking up encoders got me thinking....do the electronic geniuses here think that a home made version of a Newall encoder is possible?

If you don't know what a Newall encoder is, check out http://www.newall.com/LEDs/operation.htm

They are a very neat linear encoder technolgoy, y are accurate to like 1 micron over a meter and have no moving parts.

Unlike glass scales, maybe, just maybe, that head with the coils could be a diy project - I don't know enough about electronics to know if thats nonsence or not, but if possible it would open up cheap dro and closed loop servo bases cnc systems for the home shop, which imo would be very cool.
what do you guys think - would it be feasible and you have ideas on how to build the encoder unit??</font>

Feasibility varies directly with the depth of your pockets

The system is quite simple, and would not be too difficult to implement (obvious patent questions aside). The problem is in the balls. If you want accuracy, your balls have to be very uniform. McMaster-Carr sells a 1/16" stainless steel ball with 10 micron sphericity and 700 micron diametric tolerance for $6.26/100.

Then you have to design the circuitry, have a PC board designed and fabricated, write the DSP code, design the housing, design the ball carrier, design the mounts, design the cabling and define the connector.

Then you have to design the controller, the display, the user interface, the housing, write the microprocessor software, define the power supply. Layout the PC board and get it fabricated.

Then you must buy the parts, stuff and solder the PC boards, assemble the various components, make up the interconnecting cables.

And test it

A piece o' cake

[This message has been edited by Leigh (edited 09-07-2005).]

[Peter Sanders]

Hi

There is a 2 part (I think) article in MEW Model Engineers Workshop, on using a computer mouse as such a device. It does seem to be remarkably accurate and is very simple to make. I don't have the issue numbers.

[hammerhead74000]

Don't forget calibrating it against a known standard, too...

[Davis In SC]

I was under the impression, that the Newall unit must be "Taught" at the factory.... I saw a cutaway of the scale at a Travers Tool Customer Day. Seems like they had a utit operating under water...

[Mcgyver]

Leigh, your points are good, but basically brush everything away except the linear encoder.

The reason I say this is if one thought through a dro or closed loop cnc system for a diy perspective that didn’t' rely on screw accuracy (i.e. base on linear encoders), everything else is fairly accessible. I'm in the process of making most of the things you mentioned for a pcb mill viand have learned there is lots of open source designs and the components are not expensive.

The exception is the linear encoders, which as far as I can tell, meant glass up until these puppies. The reference is accessible to all of us, ball bearings + the electronics, while beyond my ability to design, seemed to have diy potential.

700 micron diametric sounds awful, I’m taking a micron to mean 1/1,000,000 meter or about 3/100,000 thou? I don't know specs on high class ball bearings (the ball, not TIR) but that’s what Newall says they use.

So assuming ball bearings are reasonably accurate and priced, a suitable non magnetic tube can be found, and whatever you are doing with the ttl output exists or is assumed, any thoughts on how to build one?

I willing to accept that it may be impossible, but not because of what they retail for...there has to be a technical constraint, i.e. we build lots of $500 or $1000 items in our shops for $50. Now, it may still be impossible, but if I can I'd like to find out why before giving up.

[Leigh]

<font face="Verdana, Arial" size="2">Originally posted by Mcgyver:
...So assuming ball bearings are reasonably accurate and priced, a suitable non magnetic tube can be found, and whatever you are doing with the ttl output exists or is assumed, any thoughts on how to build one?</font>

The problem is: The TTL output that you mention is the result of the processing done by the DSP. This is definitely non-trivial. I've designed many similar systems, and I can tell you that it takes some very good engineers and programmers to make something like this work, and considerable $$$.

[ibewgypsie]

Yeah,, guys...

A pair of magnetic pickups like under your car on the balancer? put two of them out of phase reading the "rack" on your lathe cross slide it'll do the same thing..

OR? I did years ago a 35mm roll film encoder. It rolled up and across, back and forth. was black as pitch and blocked the light.

One chip in it, scratches the emulsion and it is dead. So.. that ideal is kinda dead unless you remote mounted it on the wall.


ThE rolling cdrom is the way to go. CUt slots in it, using .50 worth of emitter-detector pairs.. if you have to buy interuppter modules *emitter-detector pairs you might as well buy the clarostat 128 ppr rotary encoders since they are $50.


[This message has been edited by ibewgypsie (edited 09-07-2005).]