> On Mon, 22 May 2006 13:24:04 -0700, Tim Wescott <tim@seemywebsite.com>
> wrote:
>>What's your volumes, and what's your willingness to build your own? As
>>Jim Stewart mentioned there are possibilities, but the only commercially
>>available weight (or force) sensors that I know of are all stainless
>>steel devices meant to go into an industrial setting and last forever
>>while being sprayed with salt water and whacked with hammers. That's
>>good for the guy who needs one and doesn't want to spend a lot of
>>engineering time qualifying the sensor, but not too good for a product.
>
>
> My volume is fairly low. Initially prototypes, and then 500 or so per
> year. Rolling my own seems to be the only option.
Since this is fan-fold paper being fed into a ticket printer, you could
perforate selected tickets on the edges, and use a single
opto-interuptor as the reader. That would be << $20
You could also encode information of the label types, and even
languages etc.
If your company do not want any revenuse stream from the paper, then
you can give the clients a simple punch, and tell them where to punch if
they want automatic paper alerts :)
-jg
Reply by Frnak McKenney●June 6, 20062006-06-06
On Tue, 23 May 2006 19:58:06 +0200, Anton Erasmus <nobody@spam.prevent.net> wrote:
> On Mon, 22 May 2006 13:24:04 -0700, Tim Wescott <tim@seemywebsite.com>
> wrote:
>>Anton Erasmus wrote:
>>> I am looking for a low cost weight sensor. I am trying to provide a
>>> indication of the amount of paper available. The empty container is
>>> approx. 1kg, and approx. 10kg full of paper. It should be able to
>>> handle industrial temperature range. A resolution of 1kg would be
>>> acceptable. If I can get 100g resolution, it would be great.
>>> I would prefer SPI or I2C interface, but analog out would be
>>> acceptable - something that can directly interface with a MCU.
This is a followup to a later posting (also by Anton), the original for
which seems to have been lost by news.east.earthlink.net during its
recent multi-week spate of news server hiccups. Sorry about the
incorrect threading...
>On 30 May 2006 13:21:46 GMT, Charles Allen <ca765@earthlink.net>
>wrote:
>>All sorts of clever ideas... but I'm still curious about one of the
>>ideas the original poster mentioned: A hinged rod resting on top of
>>the stack (presumably attached to a pot or some discrete switches or
>>something like that). What didn't work with that setup?
>
>It wasn't me that mentioned the hinged rod. In my case this would
>not work since although I am using a stack of paper, it is a
>fan-fold stack. The stack is placed below the dispenser, and the
>paper feeds into the bottom. The slope of the paper varies
>approximately +- 40 degrees from the vertical.
Thought I'd give this problem one last shot. Based on the above,
here's what I envision:
Dispenser
===================+
-----------------\ |
Ticket +======= \ ========+
being | \ @ |
dispensed | \ |
| \ @ |
| \ |
| / @ |<-- Ticket bin (side view)
| / |
| / @ |
| / |
| / @ |
| /------ |
| \-------------@\ |
| /--------------/ | Fan-fold ticket stack, held
| \-------------@\ | folded by gravity.
| /--------------/ |
+==================+
That is, the fan-fold ticket "thread" is (reasonably) tightly
stacked at the bottom, perhaps less so near the top, and mostly
unfolded as it nears the top of the stack bin on its way to being
fed out by mechanical or motorized means to where the recipient can
reach it.
So... a simple downward-pointing light or ultrasonic sensor would
probably always "see" the stack bin as full. Until the bin was
empty, that is (or nearly so, with the last ticket or two dangling).
Running a transparent "strip" up the side of the "bin" would allow a
human to easily see how full the bin was, but you've mentioned a
desire to be able to read the stack remotely.
Along the same lines, you could put reeeeeallly wide photo-
interruptors across the width of the bin, that is, edge-on to the
side of the ticket stack. You'd have to make them "broad-beam",
that is, set them up so that they were only "blocked" by a "packed"
stack of tickets (e.g. the bottom of the stack) and not by the
unfolding "singles" at the top of the bin and about to be fed out of
the mechanism.
Ah! _If_ the ticket stack and its unfolding really looks like my
drawing ("Hah!", says Murphy! <grin>), you could put the photo-
interruptors across one end of the bin (the left or right side as
I've drawn it, probably the right side). I've drawn them using
"@"s. This would keep the "unfolded" tickets completely away from
the photointerruptors and give more accurate results.
Then, there's idea (described previously) of using a lever arm
with a resistive or encoder deflection readout. This arm would lie
flat against one side of the bin (e.g. as I've drawn it, the front,
up off your screen) and would have a roller that ran across the bin
(in and out of my diagram) that rested on the top of the "packed"
portion of the ticket stack. It would be spring-loaded to gently
press down on the top of the stack.
If you wanted something based on weight, perhaps the tickets could
be stacked on top of a flat metal plate on top of a bin-wide coil
spring. The spring would be strong enough to keep the stack "tight"
and pressed up agains the top of the bin. Height measurement would
be done by the column of photointerruptors described above, exvept
that you'd interpret it in reverse (e.g. bin is half full when the
top half of the sensors are blocked).
Other than that, I'm about out of ideas. Hope you find something
that helps you.
Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut minds pring dawt cahm (y'all)
--
It is necessary for us to learn from others� mistakes. You will
not live long enough to make them all yourself.
-- Admiral Hyman G. Rickover
--
Reply by Anton Erasmus●May 30, 20062006-05-30
On 30 May 2006 13:21:46 GMT, Charles Allen <ca765@earthlink.net>
wrote:
>
>All sorts of clever ideas... but I'm still curious about one of the
>ideas the original poster mentioned: A hinged rod resting on top of
>the stack (presumably attached to a pot or some discrete switches or
>something like that). What didn't work with that setup?
It wasn't me that mentioned the hinged rod. In my case this would not
work since although I am using a stack of paper, it is a fan-fold
stack. The stack is placed below the dispenser, and the paper feeds
into the bottom. The slope of the paper varies approximately
+- 40 degrees from the vertical.
Regards
Anton Erasmus
Reply by Charles Allen●May 30, 20062006-05-30
All sorts of clever ideas... but I'm still curious about one of the
ideas the original poster mentioned: A hinged rod resting on top of
the stack (presumably attached to a pot or some discrete switches or
something like that). What didn't work with that setup?
--
Charles Allen
Reply by terr...@terryking.us●May 29, 20062006-05-29
How about the low-cost MEMS "Air pressure" sensors, attached to a small
plastic bag with a plastic hose. A rectangular plastic bag the size of
the tickets would only need to have about 1/4 inch of air in it and
would only deflect a small amount as the load varied from 1 to 10 Kg.
Cheap parts...
Probably linear within 5 percent.
Regards, Terry King ...On The Mediterranean in Carthage
(Back ...In The Woods In Vermont for the Summer)
Reply by Frank Bemelman●May 28, 20062006-05-28
"Anton Erasmus" <nobody@spam.prevent.net> schreef in bericht
news:jv8j72psc3to769lticp5ghqehuioksiat@4ax.com...
> On Fri, 26 May 2006 22:38:27 +0200, "Frank Bemelman"
> <f.bemelmanq@xs4all.invalid.nl> wrote:
>
> >"Anton Erasmus" <nobody@spam.prevent.net> schreef in bericht
> >news:s65c729147mk6u97ha2tn7ie4b07j8svml@4ax.com...
> >>
> >> Keep the ideas coming. Even if I cannot use it, I am sure someone
> >> someday would get something they could use out of the archives.
> >
> >Ultrasonic distance sensor?
> >http://www.parallax.com/detail.asp?product_id=28015
>
> This might work if I can get a module at low enough cost. The one
> your URL points to, is too expensive. I think there is a chance of
> getting quite a sophisticated ultra-sonic or light distance measuring
> modules at low cost.
"We have used this sort of setup, but for the current product I would
want something in the US$20 range."
They offer a 5-pack for $100.
Since you mentioned the dust problems, anything using light seems
out of the question. Depending on the mechanics, you could also use
a lever and hall sensor to get your analog value of the bin content.
--
Thanks, Frank.
(remove 'q' and '.invalid' when replying by email)
Reply by Anton Erasmus●May 28, 20062006-05-28
On Fri, 26 May 2006 22:38:27 +0200, "Frank Bemelman"
<f.bemelmanq@xs4all.invalid.nl> wrote:
>"Anton Erasmus" <nobody@spam.prevent.net> schreef in bericht
>news:s65c729147mk6u97ha2tn7ie4b07j8svml@4ax.com...
>>
>> Keep the ideas coming. Even if I cannot use it, I am sure someone
>> someday would get something they could use out of the archives.
>
>Ultrasonic distance sensor?
>http://www.parallax.com/detail.asp?product_id=28015
This might work if I can get a module at low enough cost. The one
your URL points to, is too expensive. I think there is a chance of
getting quite a sophisticated ultra-sonic or light distance measuring
modules at low cost.
Regards
Anton Erasmus
Reply by Anton Erasmus●May 28, 20062006-05-28
On Fri, 26 May 2006 17:53:09 GMT, Frnak McKenney
<frnak@far.from.the.madding.crowd.com> wrote:
>On Thu, 25 May 2006 23:35:43 GMT, Frnak McKenney <frnak@far.from.the.madding.crowd.com> wrote:
>> On Thu, 25 May 2006 22:47:31 +0200, Anton Erasmus <nobody@spam.prevent.net> wrote:
>> --snip--
>>> We have used a switch that indicates when the paper is less than a
>>> certain amount. Both mechanical and optical. The system is a ticket
>>> dispensing machine - typically used in parking lots.
>--snip--snip--
>
>(Hmph. Following up on my own post. I guess it's okay, as long as I
> don't start answering... )
>
>
>Anton,
>
>It's amazing what just a few hours' sleep can do for one's thinking.
>Scratch all that "sophisticated" stuff.
>
>Why not just put a transparent (plastic, glass) window in the side of
>the ticket dispenser so you can _see_ if any tickets are left? No
>added mechanics, no electronics, and, best of all, it would make my
>high school math teacher proud <grin!>:
>
> "Answer by inspection!"
I was thinking of using an electronic version of this. Using a piezo
sheet or other sensing material in stead of the transparent window.
As long as one can get some sort of "position" indication when the
paper is fed, one should be able to sense how much paper is
available. The type of material used for robotic hands should work.
I am not sure what sort of price one would expect to pay for these
sorts of materials.
Regards
Anton Erasmus
Reply by Anton Erasmus●May 28, 20062006-05-28
On Thu, 25 May 2006 23:35:43 GMT, Frnak McKenney
<frnak@far.from.the.madding.crowd.com> wrote:
>On Thu, 25 May 2006 22:47:31 +0200, Anton Erasmus <nobody@spam.prevent.net> wrote:
>--snip--
>> We have used a switch that indicates when the paper is less than a
>> certain amount. Both mechanical and optical. The system is a ticket
>> dispensing machine - typically used in parking lots. The people
>> employed to operate it, is minimum wage employees (Which is about
>> US$0.70 per hour in South Africa). The systems are not well
>> maintained, the environment is extremely dirty and dusty, and the
>> enclosures in which the machines and paper are housed are never
>> cleaned. I am trying to think of a way to make a cheap robust sensor
>> which would work reliably for the 10 year life expected of the
>> equipment. Being able to measure more than just a specific quantity of
>> paper left would be a bonus.
>> Counting as suggested by someone else would not work since the paper
>> is periodically added, without any way to know exactely how much had
>> been added. The paper is also fairly low quality that generates lots
>> of paper dust, that loves to cling to things like photo diodes and
>> transistors.
>
>
>Anton,
>
>Thanks for the detail; it helps a lot. A couple of questions more:
>
> 1) Are these tickets something whose construction/printing are
> under your control, and if so, to what extent?
We have the tickets pre-printed on one side, adding a black mark
for detection, and typical legal mumbo jumbo wanted by the customer.
The size, etc of the tickets are fixed, since it depends on factors
such as cost, typical size wanted, printing mechanisms used, acceptor
used etc. The amount of paper in the stack should be measurable
within the current paper definition.
> Barcodes, at least the traditional type, wouldn't help give you
> quantity, but there may be some options based on the tickets
> themselves.
We print a dynamically generated barcode on each ticket. The
dispenser does not have a barcode reader.
> 2) How precise does the measurement have to be, and what will be
> done with the information? That is, if all you care about is
> being able to turn on a LED indicating that it's time to refill
> the dispenser, what is it that makes you want more detailed
> information on the remaining ticket count?
If I can have 5 or 10 different levels it would be ideal. In smaller
sites an attendant walks around and fills up as required. On the
bigger sites, the units are networked, and there is a central office,
where one can supply information. The idea is to be able to indicate
when units have used enough paper to be able to take a typical
extra stack as normally supplied, and when the paper situation is
becoming critical. Some gates are used more than others, so a
"critical" paper situation for one can mean only 5000 tickets left,
while for another "critical" is only 100 tickets left.
> 3) How is the level monitored now? (This overlaps a bit with (2)).
No monitoring is currently done. We have done some prototypes
with field trials in the past using optical sensors, but they proved
to be unreliable in the long run . On the smaller sites having an
attend check it periodically is good enough. On the larger sites
running out of paper when it is busy is unacceptable, and because
of paying minimum wages a "supervisor" needs to know when it is
running out to send someone to add paper. Systems that worked
100% in the past when they did no pay minimum wages, are now
unreliable and the landlords are prepared to pay for a technological
solution, in stead of paying more and getting better employees.
> 4) The tickets _are_ stacked, and not dispensed from a reel or
> spool, yes? (Sorry, but I had to ask <grin>).
Yes it is a fan-fold stack which feeds from the top. One adds paper
to the bottom.
>If, for example, the attendant periodically walks around the lot and
>looks at each dispenser, you could use a simple mechanical "flag"
>attached to a lever spring-pressed against the top of the stack to
>give a "gauge" of how full the dispenser was. The flag would
>bevisible through a transparent window and would show "50% full",
>"25% full", "near empty", and "empty" or even more detail if
>desired.
As described earlier, this sort of solution worked fine in the past.
Now a "supervisor" must play policemen to make sure things are done.
The "supervisor" does not want to walk around the lot, hence wants
an indicator in his office. This situation has arisen since the
parking lot operator companies became public companies. Short term
profit is now the only thing that counts.
>Any better?
The weight sensing will work. Getting something cheap reliable which
is good enough is going to a bit more complicated than I thought it
would be.
Regards
Anton Erasmus