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alexVIA

join:2012-12-03

Help movement sensor

Hi,

I'm a student and I'm currently working on a project for a company. This project consists of create a medical matress in order to prevent bedsores.
That's the reason why I'm here, I'm looking for a movement sensor with the intention to know when the patient will move. The idea would be : if the patient doesn't move for (for example) 1 hour, trigger a program.

To give an idea, the program would be a movement of the matress, controled by 2 servo motor and 1 PLC.

If anyone would have an idea about what kind of sensor should I use, I would be grateful.

Thank you in advance.

Best regards.

Alexandre


aurgathor

join:2002-12-01
Lynnwood, WA
kudos:1
Where is the sensor located? If in the matress, I'd try some 3-axis, I2C accelerometers first.


cowboyro
Premium
join:2000-10-11
Shelton, CT
reply to alexVIA
A resistive sensor net (matrix) placed under the sheets.

alexVIA

join:2012-12-03
reply to alexVIA
Thanks both for your answers.

I think I'd prefer under the sheet as cowbovro specified.
I'd have another question : How the sensor could interfere with a program ?

Best regards


cowboyro
Premium
join:2000-10-11
Shelton, CT

1 recommendation

You'd need an acquisition interface that you can poll or which generates a signal when a change is detected (or both). The details highly depend on your desired approach (network? USB? serial port?). Keep in mind that for anything that may have potential galvanic contact with a human proper insulation from the mains is required. That means using special power supplies and amplifiers (consider acquisition sensors may be subjected to defibrillator shocks) and completely insulating the logic from the computer (optical or dedicated insulated amplifiers). I don't remember if the standard is 5000V or 7000V but it's somewhere in that range to get an idea.

b10010011
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join:2004-09-07
Bellingham, WA
Reviews:
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Considering the points cowboyro just brought up I would consider an infrared device placed over the bed and analyze the heat signature to determine if movement has occurred.
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tschmidt
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reply to alexVIA
Interesting project.

Looks like there are a lot of commercial products but probably too expensive for your design.

»www.sensorprod.com/dynamic/mattress.php

»www.xsensor.com/pressure-imaging···mattress

For lower cost something like this and device it up into multiple areas so as patient moves different sections will be activated.
»www.instructables.com/id/Flexibl···uch-Pad/

/tom

public

join:2002-01-19
Santa Clara, CA

1 recommendation

reply to alexVIA
said by alexVIA:

I'm a student and I'm currently working on a project for a company.

Looks like another company is trying to "save" money by having unpaid interns design products.


cowboyro
Premium
join:2000-10-11
Shelton, CT
reply to cowboyro
After doing some research it appears that my memory is still good... defibrillators deliver up to 5000V and a 7000V rated isolation is required... So anything that is designed must start with these values in mind and assume that there is a chance for wet bed sheets. Therefore a good layer of insulation is needed in addition to taking into account capacitive coupling between the body and the net (which will be quite significant given the surface).
Good luck, you'll need plenty of it.

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1
reply to alexVIA
said by alexVIA:

I'm looking for a movement sensor with the intention to know when the patient will move.

Inexpensive force sensitive resistors (FSR) can be used in your project. You will need at least 16 of them under the mattress configured like this sketch.

Sparkfun is selling these at $7.95 each.
»www.sparkfun.com/products/9376

said by alexVIA:

The idea would be : if the patient doesn't move for (for example) 1 hour, trigger a program.

All 16 FSRs will need to be monitored periodically by analog inputs of a microcontroller. When any of them has changed from high resistance to low resistance, you know the patient has moved.

Same microcontroller can "trigger a program" to move the mattress (?) but please discuss that problem in another thread.

alexVIA

join:2012-12-03
reply to alexVIA
Thanks everybody, all the answer in this topic are useful for me. In fact lutful, your solution would be really interesting, and pretty easy to do.
Yeah the program will move some roller under the mattress.
A last question (because I don't really know something about this) which model could be the microcontroller used for this?
Thanks again.

Bg

Alexandre


tschmidt
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said by alexVIA:

which model could be the microcontroller used for this?

This task is not very computationally intensive so you can use just about any microcontroller on the market.
So the task really boils done to which family are you the most comfortable with and has the development tools you need.

Personally I'm a fan of Microchip
»www.microchip.com/stellent/idcpl···enttools

Arduino is another option if you want to quickly hack something together.
»www.arduino.cc/

Regardless you will need to do some PCB design to interface to whatever sensor you use. If you don't want to design a PCB you can put together a prototype using DIP, rather then surface mount chip and wire-wrap. Just be cautioned a lot of newer components are not available in thru-hole design anymore.

As cowboyro See Profile mentioned will need to comply with medical safety standards.

»en.wikipedia.org/wiki/IEC_60601

»www.ul.com/global/eng/pages/offe···ul60601/

Good luck with your project, sounds interesting.

/tom

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1
reply to alexVIA
said by alexVIA:

which model could be the microcontroller used for this?

I will suggest that you purchase an off-the-shelf Arduino controller board for this project. Since you will access 16 FSRs and some rollers too, you may need a separate I/O board to connect all of them. Sparkfun also sells these items - you could buy everything in one place and support open source hardware.

I typed "FSR Arduino" in Google and found a tutorial:
»garagelab.com/profiles/blogs/tut···-arduino

Place each FSR sensor and crimped/taped connection to twisted pair cable between two foam rectangles and seal everything using plastic film. You can make one sensor module for testing (by stepping or sitting on it) while you learn Arduino programming.


lugnut

@look.ca
reply to alexVIA
On the original question, +1 for passive IR Motion detector mounted above the bed.

Sensitivity can be tuned to be as touchy as necessary and eliminates any possibility of shorting out from wet sheets and electrocuting the patient.

Also, there's plenty of off the shelf hardware available and it's not as prone to noise, failure from moisture, failure from oxidation or failure from mechanical breakage.

Honestly, if an optronic solution exists I can see no reason to go with any other option.

garys_2k
Premium
join:2004-05-07
Farmington, MI
I wonder if it could reliably read the heat signature through blankets, especially if the room is warm.

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1

1 edit
reply to lugnut
said by lugnut :

passive IR Motion detector mounted above the bed ... not as prone to noise



PIR-only motion sensors are not as robust as you think ... this particular application will need at least a dual technology (PIR + microwave) motion sensor like this:

»www.amazon.com/Visonic-Dual-Tech···_sbs_p_9

said by lugnut :

... failure from moisture, failure from oxidation or failure from mechanical breakage.

However, the mattress already has lots of electro-mechanical stuff which are even more susceptible to such failure modes than a properly sealed sensor mat under it.

The mattress manufacturer may also want a complete solution that can be embedded within the mattress.

said by lugnut :

Honestly, if an optronic solution exists I can see no reason to go with any other option.

There is ... I sort of stumbled upon it way back in 1992 during my M. Sc. research at the U of A. However, this approach currently requires a really advanced OTDR setup which will cost more than the most expensive medical bed for sure.

There is a photo in my thesis which shows three consecutive backscattered pulses from gently pressing three different points on a single fiber which was resting on foam. It was the very beginning of distributed fiber optic force/pressure sensing which is nowadays used for monitoring bridges, structures, perimeters, pipelines, etc.

You will find a reference to my thesis here: »Re: loss during "free space" propagation


harrygreco

join:2012-12-04
8700
reply to alexVIA

Re:force sensitive resistor and tactilus boddifitter

HELLO.... I'm currently working on a project for a company. This project consists of create a medical matress in order to prevent bedsores
I want to give me some information about Force Sensitive Resistor and Tactilus Bodifitter\

if you can give as much information you can, i will be grateful


SparkChaser
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Downingtown, PA
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said by harrygreco:

HELLO.... I'm currently working on a project for a company. This project consists of create a medical matress in order to prevent bedsores
I want to give me some information about Force Sensitive Resistor and Tactilus Bodifitter\

if you can give as much information you can, i will be grateful

Joke or Sarcasm or both
--
--
--
"Facts do not cease to exist because they are ignored." - Aldous Huxley


Cho Baka
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reply to alexVIA

Re: Help movement sensor

No offense to the veteran posters here, but it is more than a little creepy that someone could consider "designing" and marketing such a system by asking questions on the internet.

I'm all for sharing information and teaching, but this seems over the line to me.
--
The talented hawk speaks French.

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1
reply to harrygreco

Re:force sensitive resistor and tactilus boddifitter

said by harrygreco:

... project consists of create a medical matress in order to prevent bedsores ... give me some information about Force Sensitive Resistor and Tactilus Bodifitter

I googled Tactilus and found this comment at »www.sensorprod.com/dynamic/mattress.php

" NOTE: You may also have read about electronic sensor elements, tactile surface pressure systems, force sensing resistors (FSR), free form sensor systems, pressure sensing arrays, and matrix-based tactile surface sensors. These terms are synonymous with our Tactilus® pressure sensor. ""

They are using 32x32 array because they want to show the continuously changing resistance on a fancy color display. I had suggested 4x4 array for simple motion detection based on original poster's requirement.

By the way, do you work with alexVIA See Profile at the same company?

Anyway you can learn about FSRs and embedded programming if you follow the tutorial link posted earlier or the links at Sparkfun FSR product page. Best way to learn is to get just one FSR sensor pad working.

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1
reply to Cho Baka

Re: Help movement sensor

said by Cho Baka:

No offense to the veteran posters here, but it is more than a little creepy that someone could consider "designing" and marketing such a system by asking questions on the internet.

Sometimes companies will ask a co-op student or a new hire to "explore" some new approach on their own.


tschmidt
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Milford, NH
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reply to Cho Baka
said by Cho Baka:

but it is more than a little creepy that someone could consider "designing" and marketing such a system by asking questions on the internet.

How so?

Serendipity plays a big part in design success. The advice we provide is free and it may produce unique insights or solutions to explore.

The only thing I find a little troubling is we have two new members posting the same question.

/tom


SparkChaser
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Downingtown, PA
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reply to Cho Baka
said by Cho Baka:

No offense to the veteran posters here, but it is more than a little creepy that someone could consider "designing" and marketing such a system by asking questions on the internet.

Maybe I spent too many years in semi-secret currency industry but I'd never get into what I was doing on here. If I had a co-op doing it, he/she be gone.

However, it is an interesting thread.
--
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"Facts do not cease to exist because they are ignored." - Aldous Huxley

b10010011
Whats a Posting tag?

join:2004-09-07
Bellingham, WA
Reviews:
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reply to Cho Baka
said by Cho Baka:

No offense to the veteran posters here, but it is more than a little creepy that someone could consider "designing" and marketing such a system by asking questions on the internet.

I'm all for sharing information and teaching, but this seems over the line to me.

Why reinvent the wheel? You never know if someone has done something similar and has valuable insights that could save you both time and money unless you ask.

There are no stupid questions, only stupid people.
--
Bellingham Scanner Kicks Ass! »bhamscanner.kicks-ass.org/


SparkChaser
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Downingtown, PA
kudos:3
Reviews:
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said by b10010011:

Why reinvent the wheel? You never know if someone has done something similar and has valuable insights that could save you both time and money unless you ask.

There are no stupid questions, only stupid people.

You're missing the point ( at least mine). Research is one thing. I've spent weeks studying patents. Looking for people that invented the wheel.

When you post an idea, even anonymously as it is. You run the risk of someone running to the USPTO before you do.
--
--
--
"Facts do not cease to exist because they are ignored." - Aldous Huxley

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1
said by SparkChaser:

When you post an idea, even anonymously as it is. You run the risk of someone running to the USPTO before you do.

A time-stamped internet posting is actually sufficient proof of "prior art" which can be used to challenge a patent.
»en.wikipedia.org/wiki/Internet_a···rior_art

But most probably someone patented the first force sensing mattress decades ago and it has expired by now. There are many variations of pressure sensor mats being sold by quite a few companies.



cowboyro
Premium
join:2000-10-11
Shelton, CT
said by lutful:

A time-stamped internet posting is actually sufficient proof of "prior art" which can be used to challenge a patent.

Rounded corners anyone???