Pictures and explanation are right the

http://igor.chudov.com/projects/Brid...ct-2-CNC-Mill/

I already wired it to the PPMC control box and I am able to read the
readings (adjusted by diving by 4096 -- the pulse count) into EMC2.

What I would ilke to do is, somehow, make sure that encoder counts are
not missed due to some mistake of mine such as bad wiring,
misalignment, etc. I would like to count the index pulses separately
and compare index count with the angular position oft he spindle. They
should always stay within "1" of each other, if no counts are missed.

I have not yet figured out how to do it.

i

Ignoramus6780 fired this volley in
:

I would like to count the index pulses separately
and compare index count with the angular position oft he spindle. They
should always stay within "1" of each other, if no counts are missed.

I have not yet figured out how to do it.

Am I missing something, Ig?

How else would you determine the angular position of the spindle without
the encoder? I thought that's what it _did_.(?)

(You do have a "zero index" on that encoder disk, right?)
LLoyd

On 2010-12-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus6780 fired this volley in
:

I would like to count the index pulses separately
and compare index count with the angular position oft he spindle. They
should always stay within "1" of each other, if no counts are missed.

I have not yet figured out how to do it.

Am I missing something, Ig?

How else would you determine the angular position of the spindle without
the encoder? I thought that's what it _did_.(?)

Well, the basic equation is that there is a full revolution of the
encoder between the index pulses. If EMC2 sees a different number of
pulses than 4096 (4096 pulses make a full revolution of the encoder),
between two index pulses, thos would mean that pulses are missed. This
is what I want to check somehow.

i

(You do have a "zero index" on that encoder disk, right?)
LLoyd

"Ignoramus6780" wrote in message
...
On 2010-12-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus6780 fired this volley in
:

I would like to count the index pulses separately
and compare index count with the angular position oft he spindle. They
should always stay within "1" of each other, if no counts are missed.

I have not yet figured out how to do it.

Am I missing something, Ig?

How else would you determine the angular position of the spindle without
the encoder? I thought that's what it _did_.(?)

Well, the basic equation is that there is a full revolution of the
encoder between the index pulses. If EMC2 sees a different number of
pulses than 4096 (4096 pulses make a full revolution of the encoder),
between two index pulses, thos would mean that pulses are missed. This
is what I want to check somehow.

i

(You do have a "zero index" on that encoder disk, right?)
LLoyd

Mount a mirror on the shaft, shine a solidly-fixed laser pointer at it and
mark the spot on a far wall. When you rotate the shaft so the spot comes
back to the mark you have turned it exactly 1 revolution to an accuracy of
about 1 milliradian or better.

On Thu, 16 Dec 2010 21:08:31 -0600, Ignoramus6780
wrote:

On 2010-12-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus6780 fired this volley in
:

I would like to count the index pulses separately
and compare index count with the angular position oft he spindle. They
should always stay within "1" of each other, if no counts are missed.

I have not yet figured out how to do it.

I needed this on my lathe spindle. Turns out there was no way to do it
in Galil/Camsoft (Let me know if EMC has a way)

Don Foreman came to the rescue. A small transistor amplified the index
pulse to high speed opto 22 input. Allowed dead nuts accurate
threading at 4000 RPM. He said duck soup easy, but total fricken
mystery to me. Us MEs never quite trust those sparkEs.

Karl

On Dec 16, 9:37*pm, Ignoramus6780
wrote:
...
What I would ilke to do is, somehow, make sure that encoder counts are
not missed due to some mistake of mine such as bad wiring,
misalignment, etc. I would like to count the index pulses separately
and compare index count with the angular position oft he spindle. They
should always stay within "1" of each other, if no counts are missed.

I have not yet figured out how to do it.

i

Consider the possible and likely failure mechanisms, and balance the
consequences against the added expense of monitoring.

Initially if the encoder sensor output looks clean on a scope you
probably aren't dropping counts.
http://club.myce.com/f61/eye-pattern-195197/
http://i.cmpnet.com/digitaltvdesignl.../Monster3C.jpg
As it ages and collects dirt or shifts out of alignment you could lose
either signal. Can EMC2 compare the commanded and measured speeds and
trip an error if the difference exceeds limits?

If you want a simple hardware monitor you could divide the encoder
counts by 4096 with one of these:
http://www.fairchildsemi.com/ds/CD%2FCD4060BC.pdf
and clock a bidirectional counter down from the divider output and up
from the index.
http://www.intersil.com/products/dev...?pn=CD40193BMS
Display the count output with LEDs and occasionally check to see if it
has drifted off 0000 (all 4 off), or really that its normal pattern is
changing.

Also you could trigger one-shots with the encoder pulses and light
green LEDs with the outputs. This would detect a complete failure of
either encoder.

These could be connected to the controller to give error inputs that
it can poll occasionally instead of wasting its time looking for pulse
edge transitions.

jsw

In article ,
"anorton" wrote:

"Ignoramus6780" wrote in message
...
On 2010-12-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus6780 fired this volley in
:

I would like to count the index pulses separately
and compare index count with the angular position oft he spindle. They
should always stay within "1" of each other, if no counts are missed.

I have not yet figured out how to do it.

Am I missing something, Ig?

How else would you determine the angular position of the spindle without
the encoder? I thought that's what it _did_.(?)

Well, the basic equation is that there is a full revolution of the
encoder between the index pulses. If EMC2 sees a different number of
pulses than 4096 (4096 pulses make a full revolution of the encoder),
between two index pulses, thos would mean that pulses are missed. This
is what I want to check somehow.

i

(You do have a "zero index" on that encoder disk, right?)
LLoyd

Mount a mirror on the shaft, shine a solidly-fixed laser pointer at it and
mark the spot on a far wall. When you rotate the shaft so the spot comes
back to the mark you have turned it exactly 1 revolution to an accuracy of
about 1 milliradian or better.

I was thinking something similar, but mechanical, but this optical
approach is better.

But I would add one thing. The worry is mechanical slippage between
hollow spindle and the little adapter plug iggy made, and slippage is
greatest during rapid acceleration.

So, I would command the spindle into a long series starts, stops,
reversals, and so on, that should leave the spindle in the same angular
position as before the sequence. If no slippage, there will be little
or no difference between where the spindle ended up (as indicated with
the light beam) and the integral of the encoder output.

Joe Gwinn

On 2010-12-17, Joseph Gwinn wrote:
In article ,
"anorton" wrote:

"Ignoramus6780" wrote in message
...
On 2010-12-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus6780 fired this volley in
:

I would like to count the index pulses separately
and compare index count with the angular position oft he spindle. They
should always stay within "1" of each other, if no counts are missed.

I have not yet figured out how to do it.

Am I missing something, Ig?

How else would you determine the angular position of the spindle without
the encoder? I thought that's what it _did_.(?)

Well, the basic equation is that there is a full revolution of the
encoder between the index pulses. If EMC2 sees a different number of
pulses than 4096 (4096 pulses make a full revolution of the encoder),
between two index pulses, thos would mean that pulses are missed. This
is what I want to check somehow.

i

(You do have a "zero index" on that encoder disk, right?)
LLoyd

Mount a mirror on the shaft, shine a solidly-fixed laser pointer at it and
mark the spot on a far wall. When you rotate the shaft so the spot comes
back to the mark you have turned it exactly 1 revolution to an accuracy of
about 1 milliradian or better.

I was thinking something similar, but mechanical, but this optical
approach is better.

But I would add one thing. The worry is mechanical slippage between
hollow spindle and the little adapter plug iggy made, and slippage is
greatest during rapid acceleration.

My bigger worry is missing pulses due to shaft misalignment.

So, I would command the spindle into a long series starts, stops,
reversals, and so on, that should leave the spindle in the same angular
position as before the sequence. If no slippage, there will be little
or no difference between where the spindle ended up (as indicated with
the light beam) and the integral of the encoder output.

What I did yesterday was to buy a digital "laser" tachometer that has
a TOTAL function.

When it arrives, I will run the spindle for 3 minutes and look at
spindle position number in EMC, and will compare it with the TOTAL
number from the tach. They should differ by less than 1.0.

i

On Dec 17, 12:44*pm, Joseph Gwinn wrote:
...
So, I would command the spindle into a long series starts, stops,
reversals, and so on, that should leave the spindle in the same angular
position as before the sequence. *If no slippage, there will be little
or no difference between where the spindle ended up (as indicated with
the light beam) and the integral of the encoder output.

Joe Gwinn

Perhaps you could put the laser in the horizontal hole of a boring
head.

jsw

Joseph Gwinn wrote:

In article ,
"anorton" wrote:

"Ignoramus6780" wrote in message
...
On 2010-12-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus6780 fired this volley in
:

I would like to count the index pulses separately
and compare index count with the angular position oft he spindle. They
should always stay within "1" of each other, if no counts are missed.

I have not yet figured out how to do it.

Am I missing something, Ig?

How else would you determine the angular position of the spindle without
the encoder? I thought that's what it _did_.(?)

Well, the basic equation is that there is a full revolution of the
encoder between the index pulses. If EMC2 sees a different number of
pulses than 4096 (4096 pulses make a full revolution of the encoder),
between two index pulses, thos would mean that pulses are missed. This
is what I want to check somehow.

i

(You do have a "zero index" on that encoder disk, right?)
LLoyd

Mount a mirror on the shaft, shine a solidly-fixed laser pointer at it and
mark the spot on a far wall. When you rotate the shaft so the spot comes
back to the mark you have turned it exactly 1 revolution to an accuracy of
about 1 milliradian or better.

I was thinking something similar, but mechanical, but this optical
approach is better.

But I would add one thing. The worry is mechanical slippage between
hollow spindle and the little adapter plug iggy made, and slippage is
greatest during rapid acceleration.

So, I would command the spindle into a long series starts, stops,
reversals, and so on, that should leave the spindle in the same angular
position as before the sequence. If no slippage, there will be little
or no difference between where the spindle ended up (as indicated with
the light beam) and the integral of the encoder output.

Joe Gwinn

It's not a servo spindle, so there is no way to perform such an exercise
and return to the start position. What he could do is scribe a line
across his adapter and the spindle, run a series of
starts/stops/reverses and then visually inspect to see if the scribed
line is still in alignment.

If he's worried that his adapter is slipping in the spindle bore, which
it really shouldn't since it and the attached encoder wheel have little
mass, he should just install the adapter with some Locktite removable
threadlocker.

On 12/17/2010 04:00 AM, Karl Townsend wrote:

I needed this on my lathe spindle. Turns out there was no way to do it
in Galil/Camsoft (Let me know if EMC has a way)

As far as I know, EMC2 requires a real encoder with index on the
spindle, as it needs to accurately handle the reversal when doing rigid
tapping. Yes, this really doesn't apply to a lathe threading cycle,
but the EMC way is usually to go for mathematical purity and completeness.

Since most lathes have an extension at the rear of the spindle, it is
usually possible to rig an encoder there somehow, often using a timing
belt. I figured out how to do it on a Bridgeport 1J, where it is
practically impossible to add a sprocket to the spindle. I think the
same scheme could be used to put 3 sensors on a timing belt pulley or
gear as would almost always be found on the threading gear train of any
lathe that has a threading screw.

See http://pico-systems.com/bridge_spindle.html

Jon

On 2010-12-17, Jon Elson wrote:
On 12/17/2010 04:00 AM, Karl Townsend wrote:

I needed this on my lathe spindle. Turns out there was no way to do it
in Galil/Camsoft (Let me know if EMC has a way)

As far as I know, EMC2 requires a real encoder with index on the
spindle, as it needs to accurately handle the reversal when doing rigid
tapping. Yes, this really doesn't apply to a lathe threading cycle,
but the EMC way is usually to go for mathematical purity and completeness.

Since most lathes have an extension at the rear of the spindle, it is
usually possible to rig an encoder there somehow, often using a timing
belt. I figured out how to do it on a Bridgeport 1J, where it is
practically impossible to add a sprocket to the spindle. I think the
same scheme could be used to put 3 sensors on a timing belt pulley or
gear as would almost always be found on the threading gear train of any
lathe that has a threading screw.

See http://pico-systems.com/bridge_spindle.html

Jon, the reason why I could do it, relatively easily if you do not
count two months of thinking and false starts, is that my mill does
not use a drawbar and I could insert an adaptor into the top part of
the spindle. With a 1J head, you do not have that luxury.

i

I'd been wondering if an electronic counter would be a good solution, since
there are numerous models with varying features made for all sorts of
machine applications (counting/tachometer industrial applications).
I thought someone more familiar with integrating them into computer
applications might mention them as a good (but maybe not optimum) solution.

I have a couple of DPMs digital panel meters which are capable of reading
several types of input devices, including optical TTL quadrature encoders.
Other inputs are commonly used, from a fairly wide variety of signal
sources.

Of course a DPM by itself often requires an enclosure (or approx. 2"x5"
panel space) for mounting, but as far as a portable piece of test equipment,
they can be very versatile for monitoring a wide variety of machine
functions.
The Totalize feature is common on most industrial DPM tach/counters, and
other features are often fairly sophisticated specific programmable
functions.

Quality counters are made to easily integrate into machine electrical
systems, generally with output signal options that would likely be easily
implemented as inputs for a PC CNC application (maybe with a simple
isolation circuit).

--
WB
..........


"Ignoramus30138" wrote in message
...

What I did yesterday was to buy a digital "laser" tachometer that has
a TOTAL function.

When it arrives, I will run the spindle for 3 minutes and look at
spindle position number in EMC, and will compare it with the TOTAL
number from the tach. They should differ by less than 1.0.

i

On 2010-12-18, Wild_Bill wrote:
I'd been wondering if an electronic counter would be a good solution, since
there are numerous models with varying features made for all sorts of
machine applications (counting/tachometer industrial applications).
I thought someone more familiar with integrating them into computer
applications might mention them as a good (but maybe not optimum) solution.

I have a couple of DPMs digital panel meters which are capable of reading
several types of input devices, including optical TTL quadrature encoders.
Other inputs are commonly used, from a fairly wide variety of signal
sources.

Of course a DPM by itself often requires an enclosure (or approx. 2"x5"
panel space) for mounting, but as far as a portable piece of test equipment,
they can be very versatile for monitoring a wide variety of machine
functions.
The Totalize feature is common on most industrial DPM tach/counters, and
other features are often fairly sophisticated specific programmable
functions.

Quality counters are made to easily integrate into machine electrical
systems, generally with output signal options that would likely be easily
implemented as inputs for a PC CNC application (maybe with a simple
isolation circuit).


I think that it is easier to buy a totalizing tachometer ($66) than to
mess with integrating a counter. I actually have a counter unit, but
to get it to really work is probably time consuming. The unit is
mysterious, it has been displaying a zero on LCD for years and is not
running out of battery.

i

You've probably come up with a good solution for this particular
application, although the tach/totalizer may not be well suited for a
different application in the future.

A point for others would be that quality industrial DPM counters often have
a wide variety of features that would make them better suited for monitoring
numerous other machine functions, whether integrated into a single machine
or used as a portable instrument.

My primary machine tach is the Trexon Tachulator, which also displays SFM.

--
WB
..........


"Ignoramus30138" wrote in message
...
On 2010-12-18, Wild_Bill wrote:
I'd been wondering if an electronic counter would be a good solution,
since
there are numerous models with varying features made for all sorts of
machine applications (counting/tachometer industrial applications).
I thought someone more familiar with integrating them into computer
applications might mention them as a good (but maybe not optimum)
solution.


I think that it is easier to buy a totalizing tachometer ($66) than to
mess with integrating a counter. I actually have a counter unit, but
to get it to really work is probably time consuming. The unit is
mysterious, it has been displaying a zero on LCD for years and is not
running out of battery.

i

Wouldn't a low number of counts.. 100 counts (1 = 1%), or 360 (1 = 1 degree)
be adequate for the rotational position of a tap?

I suspect that 100 counts would be far more reliable at high (or low)
speeds, even though HSM tapping isn't an especially high speed application.

Assuming the 4096 encoder was already purchased, it would work to test the
application, but there isn't really a need for that high of a count per
rotation, is there?

--
WB
..........


"Ignoramus6780" wrote in message
...
I would like to count the index pulses separately
and compare index count with the angular position oft he spindle. They
should always stay within "1" of each other, if no counts are missed.

I have not yet figured out how to do it.


Well, the basic equation is that there is a full revolution of the
encoder between the index pulses. If EMC2 sees a different number of
pulses than 4096 (4096 pulses make a full revolution of the encoder),
between two index pulses, thos would mean that pulses are missed. This
is what I want to check somehow.

i

(You do have a "zero index" on that encoder disk, right?)
LLoyd

On 2010-12-18, Wild_Bill wrote:
Wouldn't a low number of counts.. 100 counts (1 = 1%), or 360 (1 = 1 degree)
be adequate for the rotational position of a tap?

I suspect that 100 counts would be far more reliable at high (or low)
speeds, even though HSM tapping isn't an especially high speed application.

Assuming the 4096 encoder was already purchased, it would work to test the
application, but there isn't really a need for that high of a count per
rotation, is there?

I have a US digital encoder. The encoder disc that provides pulses is
replaceable and is not very expensive, whatever it is, $10-20 or so.

Replacing the disc is easy and cheap. Mine is 1024 pulses (4096
counts). Very possibly, a lower count would work even better, say 500
counts, and could let me tap at high speed.

At this point, tapping at 500 RPM is just fine with me and I do not
feel that my needs would be served better if I could tap at 4,000 or
even 1,000 RPM. In fact, to do motor reversals with the VFD, at high
speed, is kind of taxing and I overshoot the tap position a lot. And
at 500 RPM, my encoder works fine, as evidenced by my trial today.

i

On Fri, 17 Dec 2010 14:15:30 -0600, Jon Elson wrote:

On 12/17/2010 04:00 AM, Karl Townsend wrote:

I needed this on my lathe spindle. Turns out there was no way to do it
in Galil/Camsoft (Let me know if EMC has a way)

As far as I know, EMC2 requires a real encoder with index on the
spindle, as it needs to accurately handle the reversal when doing rigid
tapping. Yes, this really doesn't apply to a lathe threading cycle,
but the EMC way is usually to go for mathematical purity and completeness.

Since most lathes have an extension at the rear of the spindle, it is
usually possible to rig an encoder there somehow, often using a timing
belt. I figured out how to do it on a Bridgeport 1J, where it is
practically impossible to add a sprocket to the spindle. I think the
same scheme could be used to put 3 sensors on a timing belt pulley or
gear as would almost always be found on the threading gear train of any
lathe that has a threading screw.

See http://pico-systems.com/bridge_spindle.html

Jon

Omniturn does it at the ass end of the spindle...

http://www.omniturn.com/bin/Spindle%...mponents.h tm


Top 10 Democrat Party Slogans

10. Bitterly clinging to aborton and taxes
9. We didnt destroy your freedoms, you can
visit them at the Smithstonian
8. If you want us to listen to your opinion, move to Europ
7. Someday none of this will be yours
6. We can't tax terrorism, so who cares?
5. Please don't vote us out!! None of us can hold a real job!
4. Why the Founding Fathers limited Government:
Racism!
3. Reducing America's carbon footprint, one job at a time.
2. America: We just cant wait to see how it ends!!
1. Making everything in this country free, except you.

On Fri, 17 Dec 2010 23:07:38 -0600, Ignoramus30138
wrote:


I have a US digital encoder. The encoder disc that provides pulses is
replaceable and is not very expensive, whatever it is, $10-20 or so.

Replacing the disc is easy and cheap. Mine is 1024 pulses (4096
counts). Very possibly, a lower count would work even better, say 500
counts, and could let me tap at high speed.

You can't replace just the disc. The pickup has a mask in front of the
sensors that matches the pitch of the lines on the disc. The sensor
does not sense the passing of the individual lines on the disc -- it
picks up light and dark transitions that result from the interference
between the disc and mask.


--
Ned Simmons

On 2010-12-18, Ned Simmons wrote:
On Fri, 17 Dec 2010 23:07:38 -0600, Ignoramus30138
wrote:


I have a US digital encoder. The encoder disc that provides pulses is
replaceable and is not very expensive, whatever it is, $10-20 or so.

Replacing the disc is easy and cheap. Mine is 1024 pulses (4096
counts). Very possibly, a lower count would work even better, say 500
counts, and could let me tap at high speed.

You can't replace just the disc. The pickup has a mask in front of the
sensors that matches the pitch of the lines on the disc. The sensor
does not sense the passing of the individual lines on the disc -- it
picks up light and dark transitions that result from the interference
between the disc and mask.



Thanks, I did not know this. In any case, I am not really in a big
need of tapping at high speed above 500 RPM, for many reasons but one
reason is that reversing of the spindle becomes harder.

i

As I was about ready to send the following statements as a follow-up post to
earlier questions, I think I determined a basic need for a signal to
monitor/track the rotation of a tap.
If the tap needs to re-enter the hole during the tapping operation, knowing
the rotational position of the tap would matter, so the tap is in sync with
the previously-cut thread.
Since CNC tapping isn't generally a pecking-type operation AFAICT, how often
would the signals from a high count encoder be any more practical than a low
count model?



My curiousity was wrt the importance of one count out of 4096 being of any
significance to the rotational position of a tap.. in real life.

I wasn't trying to suggest that tapping should be done at higher speeds in a
home shop.

If a large diameter (12"+) workpiece such as a division plate for a critical
timing or positioning application were being machined, then a 4096 count
encoder (on a rotary table, for example) would be more practical, for radial
positional accuracy.

My question, is why would anyone care if a tap's rotational position was
within 1/4096th or even 1/1024th out of position?

For testing, it's good to know if the encoder signals are being accurately
counted, but in terms of the depth of thread or almost any other tapped hole
parameters, the high count encoder rate is not significant.
It's not as if a thread needs to start at a specific position, generally.
Tapping a blind hole could require an incremental change in where the tap is
stopped, I suppose.

I could see having a relatively high count encoder on a CNC lathe spindle,
for example, to allow incremental stops for a thread or groove, but not for
a tap in a mill.
This example would be where a cutting tool on a lathe is started or
retracted from the workpiece at a specific rotational position.

As far as encoder count rates, a lower count per rotation would be more
desirable for very high speeds.. low enough as to not exceed the CNC
circuit's effective counting rate (input signal frequency).

Having such a high count for a mill spindle's rotational position doesn't
seem to have much significance (to me), as far as milling, tapping or
drilling are concerned.

As I suggested earlier.. wouldn't a low count (100 or even less) encoder
serve adequately for a mill spindle's rotational position?

--
WB
..........


"Ignoramus30138" wrote in message
...
On 2010-12-18, Wild_Bill wrote:
Wouldn't a low number of counts.. 100 counts (1 = 1%), or 360 (1 = 1
degree)
be adequate for the rotational position of a tap?

I suspect that 100 counts would be far more reliable at high (or low)
speeds, even though HSM tapping isn't an especially high speed
application.

Assuming the 4096 encoder was already purchased, it would work to test
the
application, but there isn't really a need for that high of a count per
rotation, is there?

I have a US digital encoder. The encoder disc that provides pulses is
replaceable and is not very expensive, whatever it is, $10-20 or so.

Replacing the disc is easy and cheap. Mine is 1024 pulses (4096
counts). Very possibly, a lower count would work even better, say 500
counts, and could let me tap at high speed.

At this point, tapping at 500 RPM is just fine with me and I do not
feel that my needs would be served better if I could tap at 4,000 or
even 1,000 RPM. In fact, to do motor reversals with the VFD, at high
speed, is kind of taxing and I overshoot the tap position a lot. And
at 500 RPM, my encoder works fine, as evidenced by my trial today.

i

"Wild_Bill" fired this volley in
:

Having such a high count for a mill spindle's rotational position
doesn't seem to have much significance (to me), as far as milling,
tapping or drilling are concerned.


I had an axiom I taught to all of my technicians back when we were doing
things like aligning Winchester technology drives:

"Measure everything to the absolute highest resolution your equipment
will handle. USE only the resolution you need to properly do the job."

You can throw away bits you don't need. You cannot "innovate" bits you
don't have.

LLoyd

On 2010-12-18, Wild_Bill wrote:
As I was about ready to send the following statements as a follow-up post to
earlier questions, I think I determined a basic need for a signal to
monitor/track the rotation of a tap.
If the tap needs to re-enter the hole during the tapping operation, knowing
the rotational position of the tap would matter, so the tap is in sync with
the previously-cut thread.
Since CNC tapping isn't generally a pecking-type operation AFAICT, how often
would the signals from a high count encoder be any more practical than a low
count model?

EMC waits for an index pulse to start tapping.

My curiousity was wrt the importance of one count out of 4096 being of any
significance to the rotational position of a tap.. in real life.

I wasn't trying to suggest that tapping should be done at higher speeds in a
home shop.

If a large diameter (12"+) workpiece such as a division plate for a critical
timing or positioning application were being machined, then a 4096 count
encoder (on a rotary table, for example) would be more practical, for radial
positional accuracy.

My question, is why would anyone care if a tap's rotational position was
within 1/4096th or even 1/1024th out of position?

I doubt anyone would.

For testing, it's good to know if the encoder signals are being
accurately counted, but in terms of the depth of thread or almost
any other tapped hole parameters, the high count encoder rate is not
significant.

If the controller undercounts counts, then the tap would not be in
sync with the spindle.

It's not as if a thread needs to start at a specific
position, generally. Tapping a blind hole could require an
incremental change in where the tap is stopped, I suppose.

I could see having a relatively high count encoder on a CNC lathe
spindle, for example, to allow incremental stops for a thread or
groove, but not for a tap in a mill. This example would be where a
cutting tool on a lathe is started or retracted from the workpiece
at a specific rotational position.

As far as encoder count rates, a lower count per rotation would be more
desirable for very high speeds.. low enough as to not exceed the CNC
circuit's effective counting rate (input signal frequency).

Having such a high count for a mill spindle's rotational position doesn't
seem to have much significance (to me), as far as milling, tapping or
drilling are concerned.

As I suggested earlier.. wouldn't a low count (100 or even less) encoder
serve adequately for a mill spindle's rotational position?


Say, 5/8-10 thread, has 1/10" per revolution. An accuracy of one count
out of 100, would be 0.001". Not completely insignificant for a tap,
and maybe enough to trip a following error.

Plug in your TPI and your count per revolution, to get the vertical
positioning accuracy.

i

On 2010-12-19, Ignoramus7337 wrote:
Say, 5/8-10 thread, has 1/10" per revolution. An accuracy of one count
out of 100, would be 0.001". Not completely insignificant for a tap,
and maybe enough to trip a following error.

Plug in your TPI and your count per revolution, to get the vertical
positioning accuracy.

The above calculation is way too simplistic and may be misleading.

A motion controller uses rate of change of angular position to control
speed of the Z servo motor, and a feedback loop to match two
variables.

It needs many samples of counts to establish that rate of change, so,
if there are very few counts, the calculation (interpolation of the
first derivative) may not be as good.

I am not sure if 4096 counts is too much, it probably is, but I am
fairly confident that for large taps in hard material, 100 counts per
revolution is not enough.

i

On Dec 18, 8:28*pm, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:
"Wild_Bill" fired this volley :
...
I had an axiom I taught to all of my technicians back when we were doing
things like aligning Winchester technology drives:

"Measure everything to the absolute highest resolution your equipment
will handle. *USE only the resolution you need to properly do the job."

You can throw away bits you don't need. *You cannot "innovate" bits you
don't have.

LLoyd

In analytical chemistry, where results may have to be defended in
court, we were taught to record all the digits and in parallel keep
track of error sources so we could estimate the level of certainty of
the measurements. Generally this meant knowing the calibration
accuracy. We soon learned not to trouble ourselves taking 0.0001%
readings if some other measurement in the chain was good only to 2%.
But the extra precision we recorded was useful when we got bad results
and had to backtrack to find our errors.

jsw

On 2010-12-19, Jim Wilkins wrote:
In analytical chemistry, where results may have to be defended in
court, we were taught to record all the digits and in parallel keep
track of error sources so we could estimate the level of certainty of
the measurements. Generally this meant knowing the calibration
accuracy. We soon learned not to trouble ourselves taking 0.0001%
readings if some other measurement in the chain was good only to 2%.
But the extra precision we recorded was useful when we got bad results
and had to backtrack to find our errors.

We were taught the same in high shool physics, too.

The trouble that I am concerned with, related to high counts per one
revolution of the encoder, is that encoder or the control may fail to
count them properly and may miss some.

Too few counts == low accuracy due to large vertical move per count
Too many counts == missing counts from time to time

i

Ignoramus7337 fired this volley in
:

The trouble that I am concerned with, related to high counts per one
revolution of the encoder, is that encoder or the control may fail to
count them properly and may miss some.

Too few counts == low accuracy due to large vertical move per count
Too many counts == missing counts from time to time



If missing counts is the issue, then you have two avenues of recourse:

You can use a faster processor, so that interrupt service latency is
shorter, or you can use a hardware decoder board for the quadrature
encoder, so that any time you wish to read it, it will be up-to-date.
It's not necessary to resolve every transition in software.

LLoyd

On Dec 18, 10:05*pm, Ignoramus7337
wrote:
On 2010-12-19, Jim Wilkins wrote:
...
The trouble that I am concerned with, related to high counts per one
revolution of the encoder, is that encoder or the control may fail to
count them properly and may miss some.

Too *few counts == low accuracy due to large vertical move per count
Too many counts == missing counts from time to time

i

If you use that binary counter IC you could tap off any division you
want, assuming the encoder output isn't quadrature.

Do you have a signal generator? Raise the encoder input frequency
until EMC2 can't follow it. You still might lose counts from CPU
loading at lower speeds, but it will give you an idea of the frequency
response.

jsw

On 2010-12-19, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus7337 fired this volley in
:

The trouble that I am concerned with, related to high counts per one
revolution of the encoder, is that encoder or the control may fail to
count them properly and may miss some.

Too few counts == low accuracy due to large vertical move per count
Too many counts == missing counts from time to time

If missing counts is the issue, then you have two avenues of recourse:

You can use a faster processor, so that interrupt service latency is
shorter, or you can use a hardware decoder board for the quadrature
encoder, so that any time you wish to read it, it will be up-to-date.
It's not necessary to resolve every transition in software.

Here's what I know.

1. The US Digital E5 module has a limit given by its 100,000 kHz
frequency. At 4,096 counts per rev, this means no more than 5,859
RPM. So, no problem here, since I cannot run it above 4,600 RPM ever,
and will not tap above 1,000 RPM.

http://usdigital.com/assets/general/...atasheet_1.pdf

2. I use Jon's Pico Systems hardware based encoder counter.

http://pico-systems.com/encd.html

It can count even more counts per second. I have a recollection of
what Jon was saying, but will not repeat since I am afraid I may
misremember.

3. My main concern is, what if due to whatever screwup of my adaptor
manufacturing process, the optical disc is more misaligned than the
specification permits, and thus would not count as well.

i

On Dec 18, 10:34*pm, Ignoramus7337
wrote:
...
2. I use Jon's Pico Systems hardware based encoder counter.

* *http://pico-systems.com/encd.html

It can count even more counts per second. I have a recollection of
what Jon was saying, but will not repeat since I am afraid I may
misremember.

3. My main concern is, what if due to whatever screwup of my adaptor
manufacturing process, the optical disc is more misaligned than the
specification permits, and thus would not count as well.

i

In my experience building prototype ink jet printers with encoders if
you can't see radial or axial wobble it won't be a problem. The eye
pattern test should show you how good your mechanical alignment is.
Connect right at the analog output of the photodetector, not a
buffered logic signal.

Beyond that the encoder will probably pick up speed variations from
motor cogging that would be measurable as harmonics on a spectrum
analyzer, or as timing jitter in the eye pattern. I doubt you care,
but we did since the encoder drove a phase locked loop to clock the
ink jet firing, and speed variations became stripes on the page. I
mention it because a sensitive instrument detects all sorts of
unexpected phenomena.

That board is similar to the atomic clock control interface I designed
and should be more than enough to measure spindle speed and
position,if you have enough I/O lines. You do have a possible timing
uncertainty which translates to position or speed error when you read
it unless you can afford to disable interrupts while you capture the
count and its timestamp.

jsw

Ignoramus7337 fired this volley in
:

what if due to whatever screwup of my adaptor
manufacturing process, the optical disc is more misaligned than the
specification permits, and thus would not count as well.


If your grating is misaligned with the two pickups, you'd likely get a
skipped count on every revolution, at any speed.

Did you make the pickup head adjustable? Is the grating centered well on
the shaft?

If the grating is centered and the head adjustable, you can do the
"standard" limit-to-limit kind of adjustment on it, then split the
difference, and you should be fine.

If not, spin the thing up to max (like you said you'd do), run it for a
while, then stop it, index it, and tally up the counts.

My bet is, if it's working reliably at 500 rpm, it'll probably be fine at
4K.

LLoyd

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com fired this volley
in . 3.70:

My bet is, if it's working reliably at 500 rpm, it'll probably be fine
at 4K.


I should have added that back in my "robotics" days, I hand-built quite a
number of quadrature encoders, with a few sporting 8K counts/rev, and
never had any problems making them work. At the time, all I had was a
fairly worn out Atlas 6x18 and a drill press.

I relied on a local photo-engraver to do reductions of my full-up
30"x30" drawings of the grating wheels. Inking the damned drawing on a
2K-spoke wheel was more work than any other part!

LLoyd

On 2010-12-19, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus7337 fired this volley in
:

what if due to whatever screwup of my adaptor
manufacturing process, the optical disc is more misaligned than the
specification permits, and thus would not count as well.


If your grating is misaligned with the two pickups, you'd likely get a
skipped count on every revolution, at any speed.

Did you make the pickup head adjustable? Is the grating centered well on
the shaft?

If the grating is centered and the head adjustable, you can do the
"standard" limit-to-limit kind of adjustment on it, then split the
difference, and you should be fine.

If not, spin the thing up to max (like you said you'd do), run it for a
while, then stop it, index it, and tally up the counts.

My bet is, if it's working reliably at 500 rpm, it'll probably be fine at
4K.

LLoyd

Lloyd, I will try to attach something to the spindle that can let me
very accurately make exactly one revolution (by hand), and see if the
number that EMC2 has, increases by exactly 1.000.

i

On Dec 19, 3:05*pm, Ignoramus12759 ignoramus12...@NOSPAM.
12759.invalid wrote:
On 2010-12-19, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:



Ignoramus7337 fired this volley in
m:

what if due to whatever screwup of my adaptor
manufacturing process, the optical disc is more misaligned than the
specification permits, and thus would not count as well.

If your grating is misaligned with the two pickups, you'd likely get a
skipped count on every revolution, at any speed.

Did you make the pickup head adjustable? *Is the grating centered well on
the shaft?

If the grating is centered and the head adjustable, you can do the
"standard" limit-to-limit kind of adjustment on it, then split the
difference, and you should be fine.

If not, spin the thing up to max (like you said you'd do), run it for a
while, then stop it, index it, and tally up the counts.

My bet is, if it's working reliably at 500 rpm, it'll probably be fine at
4K.

LLoyd

Lloyd, I will try to attach something to the spindle that can let me
very accurately make exactly one revolution (by hand), and see if the
number that EMC2 has, increases by exactly 1.000.

i

Can you spin it up, and look at the signals with an oscilloscope? Any
misalignment should show up as a variation of the quadrature
relationship. The A vs B signals will have to be moving in
relationship to each other in order to get a dropped count.

It seems you're not entirely confident in the U.S. Digital encoder
installation. I suppose that's why machine manufacturers generally use
enclosed, industrial-duty encoders.
There are numerous producers of quality enclosed encoders which include
sturdy bearing supports, internal signal conditioning circuits and offer
many mounting options.
There are many other features such as dirt and liquid-tight seals, various
output signal options etc.

By coupling a decent quality enclosed encoder to the mill spindle, you'd
have essentially no concerns about disk alignment, runout or proper mounting
of the individual components.

Having a few ruggedized encoders on hand, along with a good counter/tach DPM
can be very handy for checking all sorts of machine functions (mentioned
previously).

I didn't have any trouble finding an abundance of new surplus industrial
encoders some years ago, for use with a few DRO displays I was working with.
I wanted a couple to tear apart, and found quite a few used ones on eBay in
the $5-$10 range.
The majority of them will probably work well with just 5VDC, but many have
fairly wide power input ranges of ~5-30 VDC.

--
WB
..........


"Ignoramus12759" wrote in message
news

Lloyd, I will try to attach something to the spindle that can let me
very accurately make exactly one revolution (by hand), and see if the
number that EMC2 has, increases by exactly 1.000.

i