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  • Author Author: jw0752
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Analgesic Pain Cream Dispenser

jw0752

By now everyone knows that my Mom is my greatest inspiration. As she continues to degenerate with Parkinson's Disease I continue to try to come up with technology to make her daily activities easier. For some time now she has been fighting with the tube of Analgesic Pain Cream that she uses to ease the pain in her muscles and joints. In the good old days the tubes of cream came in a metal tube. As one squeezed and collapsed the tube it stayed that way. The tube could be slowly rolled up from the end and all the contents could be extracted. Now days the metal tubes are gone, replaced with springy plastic ones. While I am sure these plastic tubes are much cheaper and probably better for the environment they are a real challenge to use even for a fully coordinated adult. Each time the tube is used and released it expands and aspirates a bunch of air. Each time thereafter the tube must be squeezed until the air is out, before more cream can be obtained. When the cream is getting low one can try to roll the tube from the end towards the cap but it is like a spring and the tube is often slippery with cream from previous fights with the tube.

 

While researching pumps for my previous device I explored a small gear pump.

 

http://www.ebay.com/itm/311267253395?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

It occurred to me that this gear pump would be perfect for pumping cream from a modern plastic tube. The pump was sold as a 12 Volt pump but experiments have shown that this is way too much power. Optimal voltage for pumping the cream turned out to be between 1 and 2 volts drawing 3 amps. My initial idea was to use AA batteries to supply the power but at the draw of 3 amps this would not be practical. I had some high capacity NiMH 7.2 volt packs that had been used in a Neato Robotic vacuum cleaner. I also had a nifty little 10 Amp variable DC to DC converter that I bought on one of my binges on a Chinese electronics site a while ago. The batteries had been capable of running the Vacuum for about an hour before they had to be charged. Even at 3 Amps for each squirt of cream they should last several tubes of pain cream before they need to be recharged.

 

Here is the battery pack that will be used:

 

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Here is a picture of the device under construction:

 

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The inlet of the pump is a metal needle sticking out of the white plastic and the outlet will be through the red polyurethane hose. The red tubing will exit the box though an oblong hole in the case and rest on top of a small SPST micro switch. The idea is that a slight downward push on the tubing will activate the switch and turn on the motor. Below is a better picture of the tubing exiting the box.

 

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Since this device is more electrical than electronic I have not produce a schematic for it. The design was more or less dictated by the resources that I had available to build it. I decided to construct a protective cage around the pain cream tube which sticks up from the top of the unit. This will prevent too much stress being placed on the adapter cap which is mounted to the top of the box. Here are pictures of the cage without and with the pain cream tube installed.

 

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The last step was to produce a short video showing how the dispenser works. While there are countless dispensers of soap and other products on the market this is the only one I know that dispenses Walgreen's Analgesic Cream.

 

 

John

  • in reply to spannerspencer

    Hi Spanner,

    Thanks for your post. The gear pump seems to thrive on a slightly thicker medium as it helps seal any back flow. Actually this little pump has good enough tolerances that it will create a slight self priming vacuum. The little gear pump is really quite unique. I remember years ago gear pumps were used for oil circulation in automobile engines and driven off the same shaft that turned the distributor. I have been out of touch with auto technology for many years now so I do not know if they are still being used. Thank you for your offer of parts if I decide to build a MK. II. I will have to wait for Mom to test the present unit and then make a determination if I can make some improvements.

    John

  • Nice work John! My granddad had Parkinson's, and he'd have benefited from this a lot.

     

    I was a bit surprised that a small priming pump could pull the thicker material through, but it doesn't seem to be struggling at all. I've been playing with one myself recently (looks identical in size to yours), as a way to turn one of those nasty vaping things into a miniature smoke machine (using a glycerine and water mixture -- not the weird toxic poison most folk use them for, I feel inclined to point out!).

     

    You're making me think there are lots of cool things that all the makers and hackers out there could do with these small priming pumps. Maybe we should have a competition around putting these motors to other weird and wonderful uses? image

     

    Anyway, great work! Let me know if you're looking into building a Mk. II -- maybe we can help out with parts?

  • in reply to shabaz

    I agree, just lowering the voltage is fine, the reason I suggested PWM was that in this case the voltage is lowered below the spec of the motor and whilst it is working with this particular motor in this particular setup that may not always be the case. I've also found that a motor may require a certain voltage to start but then once going can go lower and using PWM to control it more directly than just using an off the shelf switching PSU can give you the ability to start the motor running and then get slower if needs be.

     

    There was also mention in John's original blog post that the current was too high for the AA batteries. Using a PWM based control circuit you can design your circuit to reduce the supply current requirements significantly if the duty cycle is low enough (which is already happening with the switching PSU in this case).

     

    Best Regards,

     

    Rachael

  • Brilliant solution to the problem.

     

    While all the other suggestions are workable, the one you have works for most of the tube.

    I'm guessing that any residual cream left in the tubes can be combined into another tube at some later date.

     

    I agree that manufacturing the squeezing devices could be difficult, while this provides something anyone can duplicate.

     

    Well done

     

    Mark

  • in reply to jw0752

    Hi John,

     

    You're right, PWM can have the same end effect, although you end up having to have a capacitor and perhaps inductor to smooth out the current peaks. PWM can provide flexibility but DC motors are designed for a DC supply anyway, and for a small motor it can be easier just to use a lower voltage, as you have effectively done with the DC-DC converter you used.