Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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  #1   Report Post  
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Ivan Vegvary
 
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Okay, you guys (gals?) have been answering my questions and solving my
problems for about 5 years now. Time for possible payback.

Had to get a new roll of Mylar (ouch!) for the plotter. Now that I have
plenty, I am willing to make "division strips" for any and all. Give me the
diameter of your chuck (or any fixture), I will multiply by 3.141592 and
print you a strip of Mylar (very high linear stability) with any divisions
you desire. E.g., 360, 27, 231 etc. I can number the divisions, like on a
scale. I can probably print two scales (back to back on the same side), on
a single 1" strip.
This plotter prints very accurately (HP design jet 600)

Cost? Almost free. I send you the strip and you, after receipt, send me
equivalent postage.
If you want two strips, the weight is almost nothing.

HELP! I need ideas for shipping. Product must be rolled and not folded. I
need a source of cheap shipping tubes. I used to get 24"± tubes for about
$1, but I lost my source. Office Max, etc, want about $2.50 per tube. Wife
says use toilet paper tubes. I will check with post office to see if TP
tubes are not too small. If they work I should be able to get by with less
than 2 ounces. IDEAS FOR TUBES APPRECIATED.

This offer expires in about 2 moths because sig. other will want plotter out
of the living room and back in the shop.

Email me direct with your diameter, etc.

Ivan Vegvary


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Dave Hinz
 
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On Fri, 03 Feb 2006 16:11:38 GMT, Ivan Vegvary wrote:

HELP! I need ideas for shipping. Product must be rolled and not folded. I
need a source of cheap shipping tubes.


How about a film canister, put inside a small mailer? How wide are the
strips, and can they be rolled that tight?
  #3   Report Post  
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Don Foreman
 
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On Fri, 03 Feb 2006 16:11:38 GMT, "Ivan Vegvary"
wrote:

Okay, you guys (gals?) have been answering my questions and solving my
problems for about 5 years now. Time for possible payback.

Had to get a new roll of Mylar (ouch!) for the plotter. Now that I have
plenty, I am willing to make "division strips" for any and all. Give me the
diameter of your chuck (or any fixture), I will multiply by 3.141592 and
print you a strip of Mylar (very high linear stability) with any divisions
you desire. E.g., 360, 27, 231 etc. I can number the divisions, like on a
scale. I can probably print two scales (back to back on the same side), on
a single 1" strip.
This plotter prints very accurately (HP design jet 600)

Cost? Almost free. I send you the strip and you, after receipt, send me
equivalent postage.
If you want two strips, the weight is almost nothing.

HELP! I need ideas for shipping. Product must be rolled and not folded. I
need a source of cheap shipping tubes. I used to get 24"± tubes for about
$1, but I lost my source. Office Max, etc, want about $2.50 per tube. Wife
says use toilet paper tubes. I will check with post office to see if TP
tubes are not too small. If they work I should be able to get by with less
than 2 ounces. IDEAS FOR TUBES APPRECIATED.

This offer expires in about 2 moths because sig. other will want plotter out
of the living room and back in the shop.

Email me direct with your diameter, etc.

Ivan Vegvary


A friend and I were just discussing ways to know the orientation of a
telescope's equatorial mount. One guy wants to get 12" to 15" brass
gears made and use rotary encoders. That'd work, but I was thinking
that it could also be done electro-optically with a pattern on a disc
or strip.

I'll ping him, see if he'd like to try this. I can generate a
pattern in AutoCAD and save it as a .dwg file (R-12), .dxf (R-12) or
adobe .pdf but I have no way of accurately printing it.

I wish I could figure out how those Chinese calipers get .0005"
resolution. I took one apart. The features on the capacitive scale
and reader are not nearly that small: the reader's strips are on
..025" centers and the scale's features are .100" wide with spaces
between them that look like they were routed with an .0125" dia (might
be 0.5 mm dia) endmill.

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Ivan Vegvary
 
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"Don Foreman" wrote in message
A friend and I were just discussing ways to know the orientation of a
telescope's equatorial mount. One guy wants to get 12" to 15" brass
gears made and use rotary encoders. That'd work, but I was thinking
that it could also be done electro-optically with a pattern on a disc
or strip.


Don, generate your Acad dwg, or I could do same. Be more than happy to plot
it for you.

Ivan


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Mike Berger
 
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Heh.. film cannister. I was wondering a few days ago how I'm
going to get supplies of those. They're becoming rare!
Maybe he should use cigar boxes.



Dave Hinz wrote:

How about a film canister, put inside a small mailer? How wide are the
strips, and can they be rolled that tight?



  #6   Report Post  
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Dave Lyon
 
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HELP! I need ideas for shipping. Product must be rolled and not folded.

I
need a source of cheap shipping tubes. I used to get 24"± tubes for about
$1, but I lost my source. Office Max, etc, want about $2.50 per tube.

Wife
says use toilet paper tubes. I will check with post office to see if TP
tubes are not too small. If they work I should be able to get by with

less
than 2 ounces. IDEAS FOR TUBES APPRECIATED.


People that make fireworks use cardboard tubes that are pretty cheap.


  #7   Report Post  
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Nick Müller
 
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Don Foreman wrote:

I wish I could figure out how those Chinese calipers get .0005"
resolution.


The resolution is even higher. It is 1" / 20480. Theoretical. I get a
few 1/1000mm out of them with overshampling and averaging.


I took one apart. The features on the capacitive scale
and reader are not nearly that small: the reader's strips are on
.025" centers and the scale's features are .100" wide with spaces
between them that look like they were routed with an .0125" dia (might
be 0.5 mm dia) endmill.


Have you seen what I have added to my HP in the meantime? I didn't
describe how the electronics work*). But I have put a lot of material
how the signals look like and about the mechanical arrangement of the
couppling and shielding caps.

See: http://www.motor-manufaktur.de/werkstatt/09_yadro/part_1.html


*)
Because I don't know. I have only a vague picture of it: It works with
the vernier principle and it seems that it does enhance resolution by
messuring the coupled voltage. I _guess_.
Still have to laugh when I get remembered how much fun it was to use the
HP-54645D Mixed signal scope. :-) Geee, and they sayed that I can keep
it as long as I want. What a gem!


BTW:
Hopefully at the end of this month, kits for my digital scales interface
will be available.


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige
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Lloyd E. Sponenburgh
 
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"Mike Berger" wrote in message
...
Heh.. film cannister. I was wondering a few days ago how I'm
going to get supplies of those. They're becoming rare!
Maybe he should use cigar boxes.


Nah... you can still get them by the Hefty Bag full at any full-service film
processing center.

Some amateur pyrotechnicians make tiny aerial shells with them.

LLoyd


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Dave Hinz
 
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On Fri, 03 Feb 2006 12:18:10 -0600, Mike Berger wrote:
Heh.. film cannister. I was wondering a few days ago how I'm
going to get supplies of those. They're becoming rare!
Maybe he should use cigar boxes.


I've got 2 ammo cans full of 'em, but as such, I'm getting low (film
cans, not cigar boxes).

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Don Foreman
 
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On Fri, 03 Feb 2006 18:03:02 GMT, "Ivan Vegvary"
wrote:



"Don Foreman" wrote in message
A friend and I were just discussing ways to know the orientation of a
telescope's equatorial mount. One guy wants to get 12" to 15" brass
gears made and use rotary encoders. That'd work, but I was thinking
that it could also be done electro-optically with a pattern on a disc
or strip.


Don, generate your Acad dwg, or I could do same. Be more than happy to plot
it for you.

Ivan


Cool. I'll see if the guy responds. If he does, I'd be glad to send
you a mailing tube with stamps on it. Just peel off the outer address
label.



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Richard Lamb
 
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Don Foreman wrote:

On Fri, 03 Feb 2006 18:03:02 GMT, "Ivan Vegvary"
wrote:



"Don Foreman" wrote in message

A friend and I were just discussing ways to know the orientation of a
telescope's equatorial mount. One guy wants to get 12" to 15" brass
gears made and use rotary encoders. That'd work, but I was thinking
that it could also be done electro-optically with a pattern on a disc
or strip.


Don, generate your Acad dwg, or I could do same. Be more than happy to plot
it for you.

Ivan



Cool. I'll see if the guy responds. If he does, I'd be glad to send
you a mailing tube with stamps on it. Just peel off the outer address
label.


As a word of advice onthe encoding, look up "Gray code" techniques.
the reason it's important is that in Gray code, only one bit changes at
any transition. That makes reading the position a lot less prone
to reading errors.

Just a thought...

Richard
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Richard J Kinch
 
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Richard Lamb writes:

As a word of advice onthe encoding, look up "Gray code" techniques.
the reason it's important is that in Gray code, only one bit changes at
any transition.


Encoders these days are incremental quadrature feeding a counter, not Gray
code. Gray code made sense when the electronics were costly, but not so
today.
  #13   Report Post  
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Richard J Kinch
 
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Ivan Vegvary writes:

I need a source of cheap shipping tubes.


Dumpster behind carpet shop or printing plant.

But I think you'd be better off coiling it into something like a 5 x 5 x 5
inch box at $0.18/each.

http://www.uline.com/ProductDetail.asp?model=S-4050

If you really need tubes:

http://www.uline.com/Browse_Listing_3656.asp
  #14   Report Post  
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BEAR
 
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Ivan Vegvary wrote:

Okay, you guys (gals?) have been answering my questions and solving my
problems for about 5 years now. Time for possible payback.



HELP! I need ideas for shipping. Product must be rolled and not folded. I
need a source of cheap shipping tubes. I used to get 24"± tubes for about
$1, but I lost my source. Office Max, etc, want about $2.50 per tube. Wife
says use toilet paper tubes. I will check with post office to see if TP
tubes are not too small. If they work I should be able to get by with less
than 2 ounces. IDEAS FOR TUBES APPRECIATED.



Ivan Vegvary




Carpet store dumpster - full of tubes.

_-_-bear
  #15   Report Post  
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Ivan Vegvary
 
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"Richard J Kinch" wrote in message
. ..
Ivan Vegvary writes:

I need a source of cheap shipping tubes.


Dumpster behind carpet shop or printing plant.

Richard, thanks, I've tried carpet tubes, way way too heavy. But your link
to 5" cube boxes is the obvious answer. Thanks for the link.

Ivan




  #16   Report Post  
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Richard Lamb
 
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Richard J Kinch wrote:
Richard Lamb writes:


As a word of advice onthe encoding, look up "Gray code" techniques.
the reason it's important is that in Gray code, only one bit changes at
any transition.



Encoders these days are incremental quadrature feeding a counter, not Gray
code. Gray code made sense when the electronics were costly, but not so
today.


Ah. I guess I've dated myself.
Just wondering if I got lucky...

Richard
  #17   Report Post  
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John
 
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Richard Lamb wrote:

Richard J Kinch wrote:
Richard Lamb writes:


As a word of advice onthe encoding, look up "Gray code" techniques.
the reason it's important is that in Gray code, only one bit changes at
any transition.



Encoders these days are incremental quadrature feeding a counter, not Gray
code. Gray code made sense when the electronics were costly, but not so
today.


Ah. I guess I've dated myself.
Just wondering if I got lucky...

Richard


Gray code was used on aircraft reporting altimeters because it was easy
to determine an error in coding. If any one bit was out the thing would
report wierd altitudes in sequence.

John
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Martin H. Eastburn
 
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Why not small boxes.
If you don't need 24" why buy them.

Post office has several sizes - but those are not high volume.
(and a little pricey)
Martin
Martin Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH & Endowment Member
NRA Second Amendment Task Force Charter Founder



Ivan Vegvary wrote:
Okay, you guys (gals?) have been answering my questions and solving my
problems for about 5 years now. Time for possible payback.

Had to get a new roll of Mylar (ouch!) for the plotter. Now that I have
plenty, I am willing to make "division strips" for any and all. Give me the
diameter of your chuck (or any fixture), I will multiply by 3.141592 and
print you a strip of Mylar (very high linear stability) with any divisions
you desire. E.g., 360, 27, 231 etc. I can number the divisions, like on a
scale. I can probably print two scales (back to back on the same side), on
a single 1" strip.
This plotter prints very accurately (HP design jet 600)

Cost? Almost free. I send you the strip and you, after receipt, send me
equivalent postage.
If you want two strips, the weight is almost nothing.

HELP! I need ideas for shipping. Product must be rolled and not folded. I
need a source of cheap shipping tubes. I used to get 24"± tubes for about
$1, but I lost my source. Office Max, etc, want about $2.50 per tube. Wife
says use toilet paper tubes. I will check with post office to see if TP
tubes are not too small. If they work I should be able to get by with less
than 2 ounces. IDEAS FOR TUBES APPRECIATED.

This offer expires in about 2 moths because sig. other will want plotter out
of the living room and back in the shop.

Email me direct with your diameter, etc.

Ivan Vegvary



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  #19   Report Post  
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Richard Lamb
 
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John wrote:

Richard Lamb wrote:

Richard J Kinch wrote:

Richard Lamb writes:



As a word of advice onthe encoding, look up "Gray code" techniques.
the reason it's important is that in Gray code, only one bit changes at
any transition.


Encoders these days are incremental quadrature feeding a counter, not Gray
code. Gray code made sense when the electronics were costly, but not so
today.


Ah. I guess I've dated myself.
Just wondering if I got lucky...

Richard



Gray code was used on aircraft reporting altimeters because it was easy
to determine an error in coding. If any one bit was out the thing would
report wierd altitudes in sequence.

John


They were used a lot on simulators too, and the weird read outs were great
for troubleshooting...

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Don Foreman
 
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On Fri, 03 Feb 2006 16:03:20 -0600, Richard J Kinch
wrote:

Richard Lamb writes:

As a word of advice onthe encoding, look up "Gray code" techniques.
the reason it's important is that in Gray code, only one bit changes at
any transition.


Encoders these days are incremental quadrature feeding a counter, not Gray
code. Gray code made sense when the electronics were costly, but not so
today.


Gray code is relevant to absolute encoders, not to incremental
encoders. An absolute encoder will give correct position even if
the encoder was moved during a power-down situation. However, a
nonredundant n-bit binary sequence can be arranged so all adjacent
states vary by only one bit, thus avoiding race conditions, and it
is true that inexpensive silicon (e.g., a microcontroller or
FPGA) can now easly convert those state codes to a monotonic
sequence of values. Example: adjacent binary states from 0 to 7
would be 0,1,3,2,6,7,5,4. Elex can sort that out. It gets messier
if there are 65,536 states (16 bits). Elex can still sort it out.

Mitutoyo uses a really ingenious scheme for absolute position reading
of their digital calipers. Google it if interested. It's explained
(in patentese) in a patent assigned to Mitutoyo. I think the HF
calipers may have ripped that off, don't recall when Mitutoyo's U.S.
patent was dated. I think the HF digital calipers, at $16.99 on
sale, are an incredibly good buy. I have both HF and Mitutoyo and I
see no difference in accuracy, function, feel or finish between
them.


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Richard J Kinch
 
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Don Foreman writes:

Gray code is relevant to absolute encoders, not to incremental
encoders. An absolute encoder will give correct position even if
the encoder was moved during a power-down situation.


Quadrature encoders are both incremental and absolute by virtue of the
index pulse, if you have cheap electronics, and you can tolerate homing in
the application.
  #22   Report Post  
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Nick Müller
 
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Richard J Kinch wrote:

Encoders these days are incremental quadrature feeding a counter, not Gray
code. Gray code made sense when the electronics were costly, but not so
today.


QEs are nothing more than 2 bit Gray code (only one bit changes)
connected to a counter.


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige
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Lew Hartswick
 
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Nick Müller wrote:

QEs are nothing more than 2 bit Gray code (only one bit changes)
connected to a counter.

Nick


That is an intresting "observation". I never thought of that. :-)
...lew... (retired electronics engineer)
  #24   Report Post  
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Joseph Gwinn
 
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In article ,
Don Foreman wrote:

Mitutoyo uses a really ingenious scheme for absolute position reading
of their digital calipers. Google it if interested. It's explained
(in patentese) in a patent assigned to Mitutoyo. I think the HF
calipers may have ripped that off, don't recall when Mitutoyo's U.S.
patent was dated. I think the HF digital calipers, at $16.99 on
sale, are an incredibly good buy. I have both HF and Mitutoyo and I
see no difference in accuracy, function, feel or finish between
them.


The patent number is 6,005,387, according to the back of my Mitutoyo
CD-8"PS.

To get a pdf copy of the patent, go to http://www.pat2pdf.org.

No gray codes are involved. It's an incremental encoder, and measures
distance from the last zeroing.

Joe Gwinn
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Nick Müller
 
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Lew Hartswick wrote:

That is an intresting "observation". I never thought of that. :-)


I meant: looking at the signal.

Of course QEs and Gray-code are two different things.


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige


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Nick Müller
 
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Joseph Gwinn wrote:

The patent number is 6,005,387, according to the back of my Mitutoyo
CD-8"PS.

To get a pdf copy of the patent, go to http://www.pat2pdf.org.


Thanks for that link/hint!

Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige
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jimmy
 
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"Ivan Vegvary" wrote:

snip
HELP! I need ideas for shipping. Product must be rolled and not folded. I
need a source of cheap shipping tubes. I used to get 24"± tubes for about
$1, but I lost my source. Office Max, etc, want about $2.50 per tube. Wife
says use toilet paper tubes. I will check with post office to see if TP
tubes are not too small. If they work I should be able to get by with less
than 2 ounces. IDEAS FOR TUBES APPRECIATED.
Ivan,



If you ship US Post Office Priority mail, you can get boxes for
free.

Here is a link to triangular "tubes":
http://shop.usps.com/cgi-bin/vsbv/po...=24&passFlag=4

First page of lots of Priority mail stuff:

http://shop.usps.com/cgi-bin/vsbv/po.../Priority+Mail

The boxes, envelopes and labels are free. The USPO delivers them
to your door for free. (One envelope already has Priority Mail
postage paid and of course these are not free)

--
Jim


  #29   Report Post  
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Ivan Vegvary
 
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Okay, had one taker and mailed a 360° layout for a 5" chuck this morning. I
put three copies on a strip of Mylar, gives him three chances to cut and
paste on to his chuck. Surprisingly with a 5"x9" soft pack envelope and
toilet paper tube, the whole thing weighed in at a little over 1/2 of an
ounce. Very cheap to ship. Thanks to everybody for their shipping advice.
Will change to film canisters as soon as I can scrounge up some more.

Anybody else want a 5" diameter scale? Any other scales? Let me know.

Ivan Vegvary


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Martin H. Eastburn
 
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No - maybe a field office supporting a local customer. Like I used to do in Austin.

Mitutoyo Institute of Metrology is in Aurora, Ill.
US offices :
Michigan (motor cars maybe?)
Illinois (three sites)
California (city of Industry)

Martin - using his Handbook of Metrology version 1.1 :-)

Martin Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH & Endowment Member
NRA Second Amendment Task Force Charter Founder



Joseph Gwinn wrote:
In article ,
(Nick Müller) wrote:


Joseph Gwinn wrote:


The patent number is 6,005,387, according to the back of my Mitutoyo
CD-8"PS.

To get a pdf copy of the patent, go to http://www.pat2pdf.org.


Thanks for that link/hint!



Welcome.

Interestingly, the inventor is a Swede (by the name) living in Seattle.
Wonder what the story is. Does Mitutoyo have an R&D facility there?

Joe Gwinn


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everyman
 
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Just go to the US patent website and look it up.
Karl

"Joseph Gwinn" wrote in message
...
In article ,
Don Foreman wrote:

Mitutoyo uses a really ingenious scheme for absolute position reading
of their digital calipers. Google it if interested. It's explained
(in patentese) in a patent assigned to Mitutoyo. I think the HF
calipers may have ripped that off, don't recall when Mitutoyo's U.S.
patent was dated. I think the HF digital calipers, at $16.99 on
sale, are an incredibly good buy. I have both HF and Mitutoyo and I
see no difference in accuracy, function, feel or finish between
them.


The patent number is 6,005,387, according to the back of my Mitutoyo
CD-8"PS.

To get a pdf copy of the patent, go to http://www.pat2pdf.org.

No gray codes are involved. It's an incremental encoder, and measures
distance from the last zeroing.

Joe Gwinn



  #32   Report Post  
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Joseph Gwinn
 
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In article ,
"everyman" wrote:

Just go to the US patent website and look it up.


That works, but doesn't yield a pdf file.

For the record, the US patent website is at
http://www.uspto.gov/patft/index.html.

Joe Gwinn

Karl

"Joseph Gwinn" wrote in message
...
In article ,
Don Foreman wrote:

Mitutoyo uses a really ingenious scheme for absolute position reading
of their digital calipers. Google it if interested. It's explained
(in patentese) in a patent assigned to Mitutoyo. I think the HF
calipers may have ripped that off, don't recall when Mitutoyo's U.S.
patent was dated. I think the HF digital calipers, at $16.99 on
sale, are an incredibly good buy. I have both HF and Mitutoyo and I
see no difference in accuracy, function, feel or finish between
them.


The patent number is 6,005,387, according to the back of my Mitutoyo
CD-8"PS.

To get a pdf copy of the patent, go to http://www.pat2pdf.org.

No gray codes are involved. It's an incremental encoder, and measures
distance from the last zeroing.

Joe Gwinn

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Don Foreman
 
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On Sat, 04 Feb 2006 00:04:24 -0600, Richard J Kinch
wrote:

Don Foreman writes:

Gray code is relevant to absolute encoders, not to incremental
encoders. An absolute encoder will give correct position even if
the encoder was moved during a power-down situation.


Quadrature encoders are both incremental and absolute by virtue of the
index pulse, if you have cheap electronics, and you can tolerate homing in
the application.


A once-per-rev index pulse is still ambiguous if the encoder goes thru
more than one revolution in the travel range of the moving part, not
an uncommon situation. A rotary encoder might well be geared up for
higher resolution and accuracy.

"Absolute" generally connotes being able to sense absolute position
even after a power outage during which movement occurred one way or
another. The absolute encoder knows immediately where it is without
having to hunt for an index, a fiducial mark or a limit sense
condition.
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Lew Hartswick
 
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Don Foreman wrote:

On Sat, 04 Feb 2006 00:04:24 -0600, Richard J Kinch
wrote:


Don Foreman writes:


Gray code is relevant to absolute encoders, not to incremental
encoders. An absolute encoder will give correct position even if
the encoder was moved during a power-down situation.


Quadrature encoders are both incremental and absolute by virtue of the
index pulse, if you have cheap electronics, and you can tolerate homing in
the application.



A once-per-rev index pulse is still ambiguous if the encoder goes thru
more than one revolution in the travel range of the moving part, not
an uncommon situation. A rotary encoder might well be geared up for
higher resolution and accuracy.

"Absolute" generally connotes being able to sense absolute position

----------
even after a power outage during which movement occurred one way or
another. The absolute encoder knows immediately where it is without
having to hunt for an index, a fiducial mark or a limit sense
condition.


I would even go so far as to "always" .
If it's not Absolute then it's only relative. :-)
...lew...

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DoN. Nichols
 
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According to Don Foreman :
On Sat, 04 Feb 2006 00:04:24 -0600, Richard J Kinch
wrote:

Don Foreman writes:

Gray code is relevant to absolute encoders, not to incremental
encoders. An absolute encoder will give correct position even if
the encoder was moved during a power-down situation.


Quadrature encoders are both incremental and absolute by virtue of the
index pulse, if you have cheap electronics, and you can tolerate homing in
the application.


A once-per-rev index pulse is still ambiguous if the encoder goes thru
more than one revolution in the travel range of the moving part, not
an uncommon situation. A rotary encoder might well be geared up for
higher resolution and accuracy.


That may be so -- but I think that he may have been referring to
the linear glass scales, which have one index pulse at one end, and
quadrature encoding throughout the range.

"Absolute" generally connotes being able to sense absolute position
even after a power outage during which movement occurred one way or
another. The absolute encoder knows immediately where it is without
having to hunt for an index, a fiducial mark or a limit sense
condition.


I agree. And this makes it easy to recover from an interrupted
CNC machining run.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
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Eric R Snow
 
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On Mon, 06 Feb 2006 23:54:59 +0000, (DoN.
Nichols) wrote:

According to Don Foreman :
On Sat, 04 Feb 2006 00:04:24 -0600, Richard J Kinch
wrote:

Don Foreman writes:

Gray code is relevant to absolute encoders, not to incremental
encoders. An absolute encoder will give correct position even if
the encoder was moved during a power-down situation.

Quadrature encoders are both incremental and absolute by virtue of the
index pulse, if you have cheap electronics, and you can tolerate homing in
the application.


A once-per-rev index pulse is still ambiguous if the encoder goes thru
more than one revolution in the travel range of the moving part, not
an uncommon situation. A rotary encoder might well be geared up for
higher resolution and accuracy.


That may be so -- but I think that he may have been referring to
the linear glass scales, which have one index pulse at one end, and
quadrature encoding throughout the range.

"Absolute" generally connotes being able to sense absolute position
even after a power outage during which movement occurred one way or
another. The absolute encoder knows immediately where it is without
having to hunt for an index, a fiducial mark or a limit sense
condition.


I agree. And this makes it easy to recover from an interrupted
CNC machining run.

Enjoy,
DoN.

Yet many machine tools use incremental encoders with an index along
with limit switches. To recover from lost position the machine will
move each axis to the limit switch and then reverse direction until it
senses the index. It works, but is slow. Looking at the price
difference between absolute and incremental encoders it's easy to see
why machine tool builders like the incremental encoders.
ERS
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