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'[EE]: detecting milk froth'
2001\05\26@214901 by dvanced Technika

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Hello All.

This might sound like a weird one but maybe someone can help.

I'm trying to detect when some milk froth comes to the top of a cup for an
automatic cappuccino maker. The cup will always be the same size and will
have a coffee base already in it. What i want to do is place this cup under
a nozzle and press a button so that milk froth is poured into the cup till
it reaches a set height so that the cappuccino making is more of an
automated process.

Measuring weight is a no-goer since the froth is very light can vary in
density. Using some probes may be troublesome because the froth will stick
to them over time. Timing alone is also unsuitable. A distance measurement
device which can operate over the required range (5-10cm) might be an idea
but then again i don't know how well milk froth can be sensed since it is
not very solid.

Hope someone can help.

Regards, Kresho
Sydney, Aust.

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2001\05\26@224246 by Bob Barr

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"Kresho @ Advanced Technika" <.....kreshoKILLspamspam@spam@ADVANCEDTECHNIKA.COM.AU> wrote:


>Subject: [EE]: detecting milk froth
>Date: Sun, 27 May 2001 11:45:28 +1000
>
>Hello All.
>
>This might sound like a weird one but maybe someone can help.
>

Yes, it does sound weird...

{Quote hidden}

If the height of the cup is consistent enough, could you perhaps interrupt a
light beam when the froth breaks over the top rim of the cup? (Depending on
ambient light conditions, this may or may not be feasible but it may be
worth considering.)

Given the nature of the froth, sensing its height from above could make it
very difficult to get any great degree of accuracy in your measurement.

Regards,
Bob

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2001\05\26@224857 by Alexandre Domingos F. Souza

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>If the height of the cup is consistent enough, could you perhaps interrupt a
>light beam when the froth breaks over the top rim of the cup? (Depending on
>ambient light conditions, this may or may not be feasible but it may be
>worth considering.)

       Not if you use infrared and a kind of modulation in the signal. Like IR remotes :o)

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2001\05\26@225519 by Spehro Pefhany

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At 11:45 AM 5/27/01 +1000, you wrote:
> A distance measurement
>device which can operate over the required range (5-10cm) might be an idea
>but then again i don't know how well milk froth can be sensed since it is
>not very solid.

Ultrasonic would certainly work (and would give you a measurement rather
than a go/no-go signal) but I'd explore just why time alone isn't enough.
What exactly is varying? Pressure? Temperature of the milk?
It works just fine on time alone on commercial machines.

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2001\05\26@230345 by Mark Newland

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Haven done some work with gas analysis, I know that certain gases have a
frequency of absorbtion.  Example: CO2 will let most frequencies of light pass
right thu it with no attenuation at all.  However, there are certain specific
frequencies of light where the light will be blocked if CO2 is present.  You
might need to check if "milk froth" has an absortion frequency and use that.

Maybe it has the opposite.  Instead of looking at a frequency that blocks the
light.  Maybe there is a frequency that reflects the light.  Shine a VERY
NARROW BEAM emittor at an angle, wait for the froth to get to a certain level
and look for the reflection and the other side of the angle.

"Kresho @ Advanced Technika" wrote:

{Quote hidden}

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2001\05\26@230359 by Bob Barr

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"Alexandre Domingos F. Souza" <RemoveMEtaitoTakeThisOuTspamTERRA.COM.BR> wrote:

>
> >If the height of the cup is consistent enough, could you perhaps
>interrupt a
> >light beam when the froth breaks over the top rim of the cup? (Depending
>on
> >ambient light conditions, this may or may not be feasible but it may be
> >worth considering.)
>
>         Not if you use infrared and a kind of modulation in the signal.
>Like IR remotes :o)
>
>--

Good thought to use modulated IR but -- is milk froth IR-opaque?

I haven't worked with IR except in photography but I seem to recall that
some materials don't block IR as well as they block visible light. I have no
idea how IR would work with milk froth.

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2001\05\26@232639 by Alexandre Domingos F. Souza

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>Good thought to use modulated IR but -- is milk froth IR-opaque?

       May not be opaque, but certanly will atenuate the IR a bit. Just experiment with this! :o)

>I haven't worked with IR except in photography but I seem to recall that
>some materials don't block IR as well as they block visible light. I have no
>idea how IR would work with milk froth.

       So try it! :o)

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2001\05\26@232654 by Robert A. LaBudde

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At 11:45 AM 5/27/01 +1000, Kresho wrote:
>Hello All.
>
>This might sound like a weird one but maybe someone can help.
>
>I'm trying to detect when some milk froth comes to the top of a cup for an
>automatic cappuccino maker. The cup will always be the same size and will
>have a coffee base already in it. What i want to do is place this cup under
>a nozzle and press a button so that milk froth is poured into the cup till
>it reaches a set height so that the cappuccino making is more of an
>automated process.

This is essentially a problem in optical level detection.

Why not just measure reflected light from the surface? A system should be
easy to devise that works by simple geometry.


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2001\05\27@003627 by Dave King

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I'm trying to detect when some milk froth comes to the top of a cup for an
>automatic cappuccino maker. The cup will always be the same size and will
>have a coffee base already in it. What i want to do is place this cup under
>a nozzle and press a button so that milk froth is poured into the cup till
>it reaches a set height so that the cappuccino making is more of an
>automated process.

I used to rebuild and reconfigure cappuccino machines that were imported
from Germany and Italy.  They both worked about the same. One made swill
and the other's was rather good. What they did was preheat the milk mixture
and
then run it through a blender type apparatus. The whole process was done on
timers.
Not that this solves your measurement problem but thought you might want to
know
how others are doing it.

Dave

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2001\05\27@022429 by Bob Barr

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"Alexandre Domingos F. Souza" <EraseMEtaitospamTERRA.COM.BR> wrote:

>Subject: Re: [EE]: detecting milk froth
>Date: Sun, 27 May 2001 00:18:51 -0300
>
> >Good thought to use modulated IR but -- is milk froth IR-opaque?
>
>         May not be opaque, but certanly will atenuate the IR a bit. Just
>experiment with this! :o)
>
> >I haven't worked with IR except in photography but I seem to recall that
> >some materials don't block IR as well as they block visible light. I have
>no
> >idea how IR would work with milk froth.
>
>         So try it! :o)
>

If I were the person implementing this device and wanted to give IR a try, I
certainly would. Since Kresho is the one working on the project, I'll leave
any experimenting to him. Studying the IR opacity of milk froth just doesn't
rate very high on my to-do list. :=)

I was merely trying to point out a potential pitfall to the use of IR in
this application.

Regards, Bob
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2001\05\27@082032 by -8859-1?Q?Roland_K=F6hler?=

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There are ultrasonic proximity detectors that have an analog output related
to an object's distance; they look like the inductive detectors, and are
used to detect the level of substances like tobacco or grain in industrial
process control. Maybe it also works with foam.

Regards, Roland.

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2001\05\27@092929 by mike

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As froth ought to be conductive, my first thought would be to use a
capacitive proximity sensor. This should be reasonably immune to
'gunking up' which could be a problem for optical solutions. Offset problems caused by surface contamination could be eliminated by
looking for the rate of rise instead of an absolute threshold -
capacitive sensors tend to have nonlinear distance-to-output curves,
which should help. The size of the cup should give you plenty of
sensor area (e.g. a disc round the nozzle) to minimise stray
capacitance effects.

A sealed ultrasonic sensor may work, but I'd expect something light
like froth to absorb quite a lot of sound.

On Sun, 27 May 2001 11:45:28 +1000, you wrote:

{Quote hidden}

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2001\05\27@154254 by Peter L. Peres

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Milk froth bounces light and to some extent ultrasound. Try to bounce a
light beam at 45 degrees of where the foam top ought to be when full. It
can be infrared. The beam will be spread very wide and you need to account
for this (narrow lens on both emitter and detector).

Peter

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2001\05\28@061516 by Russell McMahon

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> I used to rebuild and reconfigure cappuccino machines that were imported
> from Germany and Italy.  They both worked about the same. One made swill
> and the other's was rather good. What they did was preheat the milk
mixture
> and
> then run it through a blender type apparatus. The whole process was done
on
> timers.


Why did one make good coffee and the other bad?

RM

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2001\05\28@065121 by Maurizio Viterbini

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Russell McMahon wrote:

> > I used to rebuild and reconfigure cappuccino machines that were imported
> > from Germany and Italy.  They both worked about the same. One made swill
> > and the other's was rather good. What they did was preheat the milk
> mixture
> > and
> > then run it through a blender type apparatus. The whole process was done
> on
> > timers.
>
> Why did one make good coffee and the other bad?
>
> RM
>
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how it has come to you in mind to buy the cappuccino machine in
Germany?

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2001\05\28@113854 by John Waters

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Your application has the following characteristics:-
1. it needs indirect contact sensing.
2. there is a certain degree of uncertainness on the parameters to acquire.
3. the sensing system needs some flexibility to accomodate variation.

How about using a PC based image processing system if budget allows?


{Quote hidden}

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2001\05\28@120636 by Dan Michaels

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I have not been following this thread, so excuse me if this idea
was already suggested, but ----

use "dark" colored coffee mugs, and devise a scheme to visually
measure the width of the dark horizontal line between the top
of the cup and the top of the froth. You will have a very good
high-contrast area, which should make sensing relatively easy.

hope this helps,
- dan michaels
http://www.oricomtech.com
=========================




At 11:38 AM 5/28/01 -0400, you wrote:
{Quote hidden}

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2001\05\28@121055 by Quentin

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Have a look at the Industrial fibre optic sensor. You get quite a
variety for diffirent applications. I would use a light beam in this
case. I am sure froth will break the beam. You set the sensitivity to
what you need.
Most are 1mm Red light (Tx=LED) but you get laser versions as well
(pricy).
Omron.com
Keyence.com
And a whole lot of others.

Quentin

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2001\05\28@134858 by Dave King

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>Why did one make good coffee and the other bad?
>
>RM

They both made the coffee about the same way but
one would actually fresh grind the beans and then
press the coffee, while the other had a hopper of grounds.
The one that ground the coffee also got the water to the
right temp while the other was cooler. The other part of it
was that one was just to help the operator out ie it was meant for
bars and restaurants etc, and the other was a standalone machine
where you could walk up and plug your money in and get your coffee.


Now take a wild guess which one made the good coffee ;-]  The restaurant
machine
or the dispensing machine....... Big subtle hint,  you won't find a waiter.

Dave

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2001\05\28@135519 by Dave King

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>  how it has come to you in mind to buy the cappuccino machine in
>Germany?
>
>--
>Maurizio Viterbini

It was just a contract to convert the machines to north american power
and serving sizes. I changed the 220/240-50 power supply out and put
in a 110-60 and a few other things. I also changed the timing so it would
not over fill cups. The two standard serving sizes are different than the  #6
cups you get here.

You'll be happy to know the Italian machine was the one that made the coffee.
It was great having one around the shop to "test" all the time. Even my home
unit comes from Italy.


Dave
(oh bugger now I've gone and insulted the Germans ;-])

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2001\05\28@150944 by Dan Michaels

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>
>You'll be happy to know the Italian machine was the one that made the coffee.
>It was great having one around the shop to "test" all the time. Even my home
>unit comes from Italy.
>

Boulder cafes are full of cappucino machines, and from the looks
of it, they "all" come from Italy.

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2001\05\28@161912 by Spehro Pefhany

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At 11:38 AM 5/28/01 -0400, you wrote:
>Your application has the following characteristics:-
>1. it needs indirect contact sensing.
>2. there is a certain degree of uncertainness on the parameters to acquire.
>3. the sensing system needs some flexibility to accomodate variation.
>
>How about using a PC based image processing system if budget allows?

This solution is appealing if only for the gross overkill "nuclear
flyswatter" approach. ;-)

Best regards,
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2001\05\28@173509 by Brent Brown

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Most have ruled it out already but I think a conductivity probe could
still be worth trying out.

A few years back I made conductivity probe circuits for use in dairy
sheds (milking sheds). If set too sensitive they would act on milk
froth, which in that case was an undesireable characteristic
because we wanted to read milk level.

Perhaps a couple of narrow stainless steel probes placed as far
apart as possible to prevent froth hanging between them.You could
add another probe to measure liquid level too if that is an
advantage. Increasing the frequency of the AC bias applied to the
probes to a few hundred khz allows capacitve sensing (or even a
hybrid capacitance/conductance method), so you could use a metal
plate under the cup for the earth instead of an earth probe.

Regards,

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  spamBeGonebrent.brownspamKILLspamclear.net.nz

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2001\05\28@183739 by Robert A. LaBudde

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At 09:36 AM 5/29/01 +1200, Brent wrote:
>Most have ruled it out already but I think a conductivity probe could
>still be worth trying out.
>
>A few years back I made conductivity probe circuits for use in dairy
>sheds (milking sheds). If set too sensitive they would act on milk
>froth, which in that case was an undesireable characteristic
>because we wanted to read milk level.
>
>Perhaps a couple of narrow stainless steel probes placed as far
>apart as possible to prevent froth hanging between them.You could
>add another probe to measure liquid level too if that is an
>advantage. Increasing the frequency of the AC bias applied to the
>probes to a few hundred khz allows capacitve sensing (or even a
>hybrid capacitance/conductance method), so you could use a metal
>plate under the cup for the earth instead of an earth probe.

Contact measurements would not be allowed under the Model Food Code.
================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: .....ralspam_OUTspamlcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
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"Vere scire est per causas scire"
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2001\05\28@192601 by Stephen B Webb

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> This is essentially a problem in optical level detection.
>
> Why not just measure reflected light from the surface? A system should be
> easy to devise that works by simple geometry.

Simple geometry?  As in: incident light at some known angle, sense
where the reflected light hits, and figure out distance from that?  I
would expect  the reflectance properties of milk froth to vary quite a
bit.

Hmm...

-Steve

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2001\05\28@193506 by michael brown

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----- Original Message -----
From: "Stephen B Webb" <TakeThisOuTsbwebb0.....spamTakeThisOuTSAC.UKY.EDU>
To: <TakeThisOuTPICLISTKILLspamspamspamMITVMA.MIT.EDU>
Sent: Monday, May 28, 2001 6:25 PM
Subject: Re: [EE]: detecting milk froth


> > This is essentially a problem in optical level detection.
> >
> > Why not just measure reflected light from the surface? A system should
be
{Quote hidden}

I'm glad they don't measure how full a glass of draught beer is this way.
;-D

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2001\05\28@202114 by victor Faria

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would the froth carry current?
what  I'm thinking is  2 contacts apart from each other and let the froth
make the contact ....
so you would have the two contact points at the same height as the cup.
when the liquid level rose to that point you would get a signal.
I maybe way off here but it is a thought.
{Original Message removed}

2001\05\28@203805 by Brent Brown

picon face
> Contact measurements would not be allowed under the Model Food Code.

I'm not familiar with that - does it relate to hygene of the contacts or
the current?

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  .....brent.brownspamRemoveMEclear.net.nz

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2001\05\28@225122 by Robert A. LaBudde
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At 07:25 PM 5/28/01 -0400, you wrote:
> > This is essentially a problem in optical level detection.
> >
> > Why not just measure reflected light from the surface? A system should be
> > easy to devise that works by simple geometry.
>
>Simple geometry?  As in: incident light at some known angle, sense
>where the reflected light hits, and figure out distance from that?  I
>would expect  the reflectance properties of milk froth to vary quite a
>bit.
>
>Hmm...

If you shine a red led, e.g., on the foam and see a red dot, then you have
enough s/n to design a sensor system around.

Geometry would specify how to position the transmitter/receiver pair so
that no signal is returned when the level is low, but happens when the
level is high.

Foam is quite reflective.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: RemoveMEralspamspamBeGonelcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
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2001\05\28@225544 by Robert A. LaBudde

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At 12:39 PM 5/29/01 +1200, you wrote:
> > Contact measurements would not be allowed under the Model Food Code.
>
>I'm not familiar with that - does it relate to hygene of the contacts or
>the current?

If the sensor probe enters the cup, it will get dirty with milk and sugar.
It then remains unrefrigerated and contacts every other cup filled. This is
unacceptable hygiene. Some means of cleaning and sanitizing the sensor
would be necessary on a periodic basis.

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Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
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Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
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2001\05\29@072037 by Bob Ammerman

picon face
> Foam is quite reflective.

Yeah, it _is_ white, after all. :-)

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\05\29@090018 by Robert A. LaBudde

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face
At 07:13 AM 5/29/01 -0400, Bob wrote:
> > Foam is quite reflective.
>
>Yeah, it _is_ white, after all. :-)

I was going to add that to the line, but it seemed a bit much after
mentioning "red spot" and "quite reflective".

A wavelength bandpass filter over the receiver and a LED transmitter would
also be helpful.

The weak point with all of these ideas lies with the real world: If you've
ever had to clean an expresso machine, you'd notice how coffer and milk
splatters all over everything. How will any sensor system be kept
operational over time?

Conductivity and other contact-based methods have the hygiene issue to
contend with. So you've got a CIP problem to also solve.

Another possibility is to use a temperature sensor. When the headspace
becomes reduced because of the froth, the temperature of the air above may
be a reliable indicator of fill level. Another possibility is a 0-100% RH
sensor, since the headspace humidity may be usable with a threshold.

Of course, as I believe was already mentioned, if you design the mechanical
part of the system correctly, the electronics becomes simpler: just measure
weight or volume dispensed, since the system fills consistently enough.
This method is simple enough to work by time alone and is practical in the
field.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: TakeThisOuTralspamspamlcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
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2001\05\29@114740 by Stephen B Webb

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face
> >Yeah, it _is_ white, after all. :-)
>
> I was going to add that to the line, but it seemed a bit much after
> mentioning "red spot" and "quite reflective".

Quite reflective, yes.  But you don't know the geometry of the froth ahead
of time.  The froth I am used to has peaks and valleys.  Could the dot get
lost among these?  How does the shape of the foam change how the light is
reflected? (is milk froth highly specular? lambertian?).  Does this
force you to use a larger spot?  Does "cold" foam have signficantly
different reflectance properties than "hot" foam (bubble size, etc).  Does
ambient light present a problem?  How can you guarantee that the sensor
is aligned properly to see a dot?  Do you use an array of sensors?  A
larger sensor?  Maybe you project a stripe instead of a spot?  How fast
does the froth level change?  How long do you need to see a spot before
you signal the machine to stop frothing?  A quick change in froth level
might put the spot past the sensor.  Larger detection area?  More than
one sensor?  Does the froth create steam that will attenuate the light?
What if the steam condenses on the emitter or sensor?

In my original message I was just trying to say that it involved more than
simple geometry.

-Steve

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2001\05\29@123557 by Robert A. LaBudde

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At 11:46 AM 5/29/01 -0400, Steve wrote:
>Quite reflective, yes.  But you don't know the geometry of the froth ahead
>of time.  The froth I am used to has peaks and valleys.  Could the dot get
>lost among these?  How does the shape of the foam change how the light is
>reflected? (is milk froth highly specular? lambertian?).  Does this

The froth is composed of bubbles. You will get a pseudo-Lambertian
scattering distribution, as specular reflection from many bubbles are
composited. The net effect is that you will see significant reflected light
over a significant cone angle.

>force you to use a larger spot?  Does "cold" foam have signficantly
>different reflectance properties than "hot" foam (bubble size, etc).  Does
>ambient light present a problem?  How can you guarantee that the sensor
>is aligned properly to see a dot?  Do you use an array of sensors?  A
>larger sensor?  Maybe you project a stripe instead of a spot?  How fast

Use a laser pointer and your cappuccino to verify the red dot is easily
visible to the eye. Then use a high power LED and a tuned receiver
(photodiode with covering filter?) and a geometric aperture to make sure
the line of sight of the receiver does not intercept the dot until the foam
is high enough. You do this by pointing the transmitter into the cup and
point the receiver aperture towards the top far edge of the cup or slightly
higher.

>does the froth level change?  How long do you need to see a spot before
>you signal the machine to stop frothing?  A quick change in froth level
>might put the spot past the sensor.  Larger detection area?  More than

The issue of timing is part of any solution to the problem. It may, in
fact, drive the requirements (limits) on accuracy, since the capacitance of
the delivery mechanism and the ability to do it consistently are limited by
the mechanical design of the equipment.

>one sensor?  Does the froth create steam that will attenuate the light?
>What if the steam condenses on the emitter or sensor?

Yes, you have to worry about false alarms due to reflections from steam,
the delivery stream, etc. A larger dot will improve your noise immunity.
Off-axis  dual sensors will also help. Wait to turn on the transmitter
until the last seconds at the boundary of the timing interval for fill.

As I mentioned in the last email, the resultant solution to this problem
will probably end up being simple delivery timing with no sensors at all
(except perhaps volume or weight in lieu of time). (Although one way of
cleaning the receiver and transmitter windows would be to run a hot rinse
water stream every time over them at the beginning of the fill.)

The FIRST thing you should do is to define and quantify the requirements
for the system proposed. How much tolerance on foam height do you have?
Must the foam never spill over? What is the minimum liquid fill level in
the cup?

The SECOND thing you should do is a statistical analysis of the foam level
variability for constant delivered volume. You'll need this anyway to
validate whatever concept you propose as a solution. Also find out the
variability of cup-to-cup volume.

The THIRD thing you should do is to see if the most trivial concept (simple
open-loop timing or volume delivered) will meet your mission requirements.


================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ralEraseMEspamlcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
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2001\05\29@162442 by Dan Michaels

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face
Stephen B Webb wrote:

>Quite reflective, yes.  But you don't know the geometry of the froth ahead
>of time.  The froth I am used to has peaks and valleys.  Could the dot get
>lost among these?  How does the shape of the foam change how the light is
>reflected? (is milk froth highly specular? lambertian?).  Does this
>force you to use a larger spot?
.......
 Maybe you project a stripe instead of a spot?
........


Steve, good thinking. There are systems that project a "grid"
[square or circular, app-dependent] onto a target, for visual
determination of various spatial properties.

A circular grid projected into the bottom of the coffee cup
would certainly appear very different as the level of fluid
changes.

Unfortunately, doing the processing for this might be rather
involved, but certainly the spatial frequency of the perceived
grid is going to decrease mightily as the level rises, esp
if the pickup sensor is relatively close to the top of the
cup rim.

- dan michaels
http://www.oricomtech.com
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'[EE]: detecting milk froth'
2001\06\01@173259 by Peter L. Peres
picon face
I've watched a machine work in a pub today and it seems to put the froth
in *before* the coffee. Maybe it's the beer but I saw this done twice in a
row. Or it's yet another kind of coffee.

Peter

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2001\06\01@184907 by Spehro Pefhany

picon face
At 10:11 PM 6/1/01 +0300, you wrote:
>I've watched a machine work in a pub today and it seems to put the froth
>in *before* the coffee. Maybe it's the beer but I saw this done twice in a
>row. Or it's yet another kind of coffee.

Yes, that's how the controls I designed worked. The foam is metered out
while the coffee beans are grinding. The nozzle is cleaned with a blast
of steam and then the brew cycle commences. The order has more to do with
minimizing the cycle time and using shared resources (the flow meter).
The brew and steam are independent thermocouple-controlled temperatures.

Best regards,
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