Active alternating air cushions???

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Re: Active alternating air cushions???

Postby Burgerman » 05 Sep 2018, 09:58

I or we are confusing units. mpa baffles me! Your sensor may be good. Although why you need to run an arduino for a pump timer confuses me. And adds complication.

The pump run at pressures like the spec of my professional bought pump. It reads:
Pressure: 70~90 mmHg. And can be set lower. 60 seems about right in use for me.

And being british we use P.S.I. for pressures usually. So thats approx 1.75psi max.
http://www.endmemo.com/sconvert/psimmhg.php
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Re: Active alternating air cushions???

Postby snaker » 06 Sep 2018, 08:58

For those prefer programmable boards, I found a very good pressure sensor.
https://item.taobao.com/item.htm?spm=20 ... 0b5311e301

But the price is fairly high, about $10 for each. Shirley, is there any cheaper alternative? I just need sensors that are relatively accurate and ... cheap :mrgreen:

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Re: Active alternating air cushions???

Postby snaker » 08 Sep 2018, 08:39

BM, can you post the link where you bought your solenoid valves?
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Re: Active alternating air cushions???

Postby Burgerman » 08 Sep 2018, 08:58

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Re: Active alternating air cushions???

Postby snaker » 08 Sep 2018, 09:50

Do its specs mean that 100cc 300mmHg tank can be empty through the opened valve in less than 3s? If so, is this speed too fast? In case an air cushion, if the valve is opened, the cushion will be empty in a very short time (e.g 15s). And a pressure cycle high-low-high will complete too fast. That is not a good alternating, isnt it?

Air speed: <3s (100cc tank from 300mmHg to 15mmHg)


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Re: Active alternating air cushions???

Postby Burgerman » 08 Sep 2018, 10:29

It only releases the air, after the opposite cells are at full pressure. Triggered by the opposing cells pressure switch. In my case I will have the switches do 2 things.
Turn off pump1, and release air from pump 2. And...
Turn off pump2 and release pressure from pump1.

So they are cross linked. Meaning at any given time one group of cells is always at full pressure. Theres never a time where one is deflating while the other is inflating.

So it doesent matter how fast it empties. But you can easily slow it by fitting a short tube to the other end of the solenoid. With a restrictor, like a small control oriface. Say a small brass control jet if you need to slow it down. Or in your case with arduino you can send it a 50% pulse, or 25% pulse, at 5 hz. To make it half or a quarter the flow.
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Re: Active alternating air cushions???

Postby Burgerman » 08 Sep 2018, 10:56

Meaning no arduino required. Just 2 simple timers. Linked to remain in sequence like this. https://www.ebay.com/itm/DC-12V-Dual-Pr ... 2749.l2648

In fact you really only need 1 timer, with single normlly open, and normally closed output. But the above allows say 10 seconds overlap time. And or easy switching to have all inflated while you transfer.

It can use an analog pressure switch (has adjustable trigger voltage) or not your choice.

Read the chinglish:

EAZY-VLC 2.0 controller can be achieved by adjusting the timing of the joint action approach dual relay, two time relay can be independently timed pull respectively, can also be individually timed turns to pull, and can control the time of the relay by detecting dual voltage.
By using this product, you can control two loads simultaneously or alternately on and off, such as: single-phase motor control timer reversing all the way, or the way the timing Reversible DC motor, or two-way solenoid valve timing control work in rotation(controlled pneumatic), or two-way indicator turns off and so on. Multiple boards can be cascaded to achiece multi-channel timer turns off cycle.

Features:

Four digital tube display, three keys for easy operation, restore factory settings function.
High performance control chip for high stability and low power consumption.
The tube display can be automatically shut down, has power supply reverse connecting protection.
Dual time relay, adjustable timing range: 0.1-9999 minutes, can be single time or cycle and release; adjustable cycle number 0-999(zero for the infinite loop).
Each relay contacts for common point and normally open, normally closed point, a total of two sets of transformation.
Dual time relay can joint action in turn; multiple boards can be cascaded to achieve multi-channel timer turns off cycle.
Dual time relay can run independently at the same time, can use high level or switch trigger start mode(P-4).
Dual voltage detection control dual time relay, detecting voltage range: DC 0-99.9V.
All setting parameters can be stored after power off, and operates the last mode and parameters when power on.

Modes Selection:
P-1: A channel time (time) relay
P-2: B channel time (time) relay
P-3: A, B two way joint time relay (A first and then B, can recycle)
P-4: A, B two way independent time relay (A, B independent cycle time at the same time)
P-5: A, B dual voltage control time relay
P-6: Digital tube automatically turn off time and reset

Specifications:
Relay Voltage: DC 12V
Working Power: DC 10-16V
Voltage Detection Range: DC 0-99.9V
Error: (+/-)0.1V
Timing Range: 0.1-9999 minutes Adjustable
Cycle: 0-999 times Adjustable
Two way, each of a set of transformations(normally open/normally closed)
Contract Load: 10A/277V AC, 10A/30V DC
Contract Resistance: ≤100mΩ(1A-6V DC)
Mechanical Durability: >10 million times
Electrical Durability: >100,000 times (10A-250V AC)
Working Current: 18mA 12V, Min. Standby Current: 7mA/12V
Working Temperature: -40-85°C
Dimension: 107 * 48 * 17mm / 4.21 * 1.89 * 0.67in
Weight: 55g / 1.95oz
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Re: Active alternating air cushions???

Postby ex-Gooserider » 11 Sep 2018, 04:09

Not sure if they would be the right pressure range or not, (I suspect they might be to low pressure) but it might be worth looking at the pressure switches they use in clothes washing machines to tell when the tub is full... They stick them up near the top of the tub with a hose to the bottom, so that they open and close as the pressure changes...

Some models are adjustable...

I used it as a check device on a pool pump controller - if the pump was actually producing pressure it was OK, but if the pump wasn't running, or if it wasn't making pressure because the skimmer was clogged or the water level was low, it triggered a shutdown....

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Re: Active alternating air cushions???

Postby ex-Gooserider » 07 Oct 2018, 05:49

Bringing this back up to add a possible info source... A week or so ago the Open Source Hardware Association had their annual conference here in Boston, and among the other presentations was a guy showing off his work on "soft robotics" which is the concept of using low pressure air to power various sorts of robotic gear, some practical some more artistic... He had created a microcontroller based addon board system called " Programmable Air".... It works in the sort of pressure range needed for a cushion. I had a quick discussion with the guy and he said it wasn't something he had tried, but that he thought it would be a possible application.

Main site:
https://programmable-air.com/

Hack a Day online articles about it
https://hackaday.io/project/129278-programmable-air
https://hackaday.com/2018/09/22/maker-f ... mable-air/

Github source page
https://github.com/tinkrmind/programmable-air

I thought it was interesting both in and of itself, but also because he has some good discussion of the general problem and some of the stuff (including parts references) that he both experimented with and ended up using...

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Re: Active alternating air cushions???

Postby Burgerman » 07 Oct 2018, 14:30

Ebay
https://www.ebay.co.uk/itm/Wheelchair-C ... SwhT1bHjYl

Cushion has 4 zones. And a cover. Is £108 UK pounds.
-Inflate green, and blue outer edges/front to 2psi, firm, and permanently.
-ALTERNATE the central rear yellow and pink areas with your pump every 5 mins.
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Re: Active alternating air cushions???

Postby tutatu » 15 May 2019, 20:11

Does this type of cushion's material allow inflating while sitting on it?

I'm asking because for example, Roho's recommendation is to overinflate and when you sit on it, then release air from cushion to accommodate your needs.

I was lying on an alternating air mattress in hospital for two months and was a lifesaver because not all nurses know how properly turn quadriplegic. To avoid potential skin shear and pulling and various nurses turning skills, with alternating mattress I could be lying longer periods of time on either side with zero redness on the skin.

What I didn't like about alternating mattress is when you finally find a comfortable angle to fall in sleep, chambers take inflate/deflate cycle and my body totally change lying position + sheats are slippery on that kind of plastic rubber material.

And yes, the buzzing of compressor/pump drives me insane, especially in the night when everything is quiet.

Driven by logic, if the mattress is good then why can't be a cushion.

After flap surgery on left coccycyxcyx in 2016, I still have a great danger to destroy skin if I would sit 10 days for 12 hours. Now I'm sitting 6 hours max.

I have high Roho but tied down 4 cells to avoid direct pressure. The hole is filled with 5-6 cm of memory foam to prevent negative pressure to that area. For now, it works.

I'm very interested in your project. :ugeek:
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Re: Active alternating air cushions???

Postby tutatu » 15 May 2019, 20:21

Now I see. Neoprene like Roho. http://www.singa.com.tw/en-suit.htm

Just nowhere to find is it alternate possible?
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Re: Active alternating air cushions???

Postby flagman1776 » 15 May 2019, 22:27

I can find the bumpy inflating cushion but can't find the automatic air pump / controls. I could see hanging the pump & controls off the side of the chair, below seat level.
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