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UVA

High-power ultraviolet flashlight for curing UV adhesive (https://bit.ly/FldRdy-DB)

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When a humanitarian crisis hits, Local communities are in the need of relief, recovery and reconstruction. To do so, it is necessary to have the tools for these tasks in a faster, better and cheaper way than today's supply chain. NGOs have to be effective in delivering their aid and people should be empowered with the knowledge and the skills to face the crisis by themselves in a resilient way.

UVA offers much more than a UV-A light tool for curing glues in adverse situations. It is a multi tool kit system designed to encourage people to create their own exchangeable instruments relying on a battery pack and a plug and play connection. UVA is based on the ideas of cost-effectiveness, local production, reparability, hardiness and intuition. It is designed with the most common and available components in the market to increase its accessibility. We have the conviction that most of the mechanical parts of the system should be produced locally with 3d printing and recycled material


Table of Contents:

Design Specifications

  • Requirements by Field Ready
  • Introduction to the UV curing process
  • Market research on available UV flashlights

Led Power System

  • Choosing the UV LEDs
  • LED bulb thermal design
  • High-efficiency LED driver circuit
  • Switching voltage regulator for the LEDs

Rechargeable Battery System

  • Choosing the Batteries
  • Designing a battery protection system
  • Integrated Li-ion battery charging circuit
  • Input power-path multiplexing

PCB Design

  • Designing a testable and reparable PCBs
  • Soldering SMD cheaply with sand
  • Writing a troubleshooting and testing manual

Manufacturing

  • Assembling and disassembling instructions

Testing Procedures

  • Testing the LED drivers
  • Testing the voltage regulator
  • Testing the battery protection circuit
  • Testing the battery charger
  • Testing the power-path multiplexer
  • Integration testing the whole system

  • UVA Joint_V1

    Miguel Fernández07/18/2020 at 12:33 0 comments

    To achieve a multi-tool kit it is necessary to understand the parts of it. This system is composed of two main elements: The battery pack and the Instrument or tool (in this case the ultraviolet light for curing adhesives).

    It's a simple idea based on one challenge, the joint. This is also the most important mechanical part of the design because it is the starting point for the development of different tool-heads. The UVA joint has to achieve 4 principles:

    1. Simplicity (to encourage people to develop new tools)
    2. Durability (It has to resist the wear of daily connection/disconnection and also the falls and shocks)
    3. Reliability (the user should be confident that the electrical and mechanical joint wouldn't fail and the tool will work as it is expected)
    4. Replaceability (The modular design of the UVA system allow to replace the chassis where the joint is build in without affecting the electronics).

    With these bases in mind, we design a rotational joint that is structured by three different connections: the snap-fit cantilever, the electrical contact and the Locks. It is necessary to leave some tolerance (in our case 0.4mm) because FDM prints are not 100% accurate. Calibration, environmental conditions and human interaction could affect the quality of the finished pieces. We need a tight fit because we have to prevent movement between the battery pack and the tool, but also we need to prevent the plastic to fail, crack or to not fit at all.

    To fit the part it is necessary to make a 28 degrees rotation in the longitudinal axis. It will snap by this rotation and do not return to the starting point without some force. Every connection has its mission to constraint the parts together.

    1. Snap-fit cantilever: this part is the most complex to design and is the one that ensures that the UVA joint will keep together the battery pack and the tool. It makes a restriction in the rotation after the snap. This rotation restriction could be broken after applying some force to unlock the uva joint.
    2. Locks: This connection is responsible for avoiding the movement in the vertical axis. The locks will help to reduce or eliminate the forces over the snap-fit cantilever after the snap, increasing the quality of the joint and the durability of the connections.
    3. Electrical connection: This part is under development. It will be the mechanism responsible to transmit the electricity between the battery pack and the tool.

    The joint was modeled with Autodesk Fusion 360, here the link to the model: https://a360.co/2OywktE

    We are going to be using this software because it is free and tremendously good for mechanical design. It can also be use to simulate electrical circuits. 

    Here some information that we used to design the UVA joint:

    About conections:

    https://www.3dhubs.com/knowledge-base/how-design-snap-fit-joints-3d-printing/

    https://drive.google.com/file/d/1E7P1v8KytKME5-KJwtn3b6-2PuZkFO8J/view?usp=sharing

    https://drive.google.com/file/d/1D9oW7FTgxugsrYvvysp96yshwzoi6t6p/view?usp=sharing

    Snap-fit design calculator:

    https://plastics-rubber.basf.com/northamerica/en/performance_polymers/services/service_calculation_programmes.html

    About PLA:

    friction coefficient: 0.492

     https://www.researchgate.net/publication/330003074_Wear_and_coefficient_of_friction_of_PLA_-_Graphite_composite_in_3D_printing_technology

    Secant modulus: 3300 Mpa

    http://www.matweb.com/search/DataSheet.aspx?MatGUID=ab96a4c0655c4018a8785ac4031b9278

    Allowable material strain: 3%

    https://www.researchgate.net/publication/257608973_Enhanced_ductility_of_polylactide_materials_Reactive_blending_with_pre-hot_sheared_natural_rubber

  • Choosing the UV LEDs

    Said Alvarado Marin07/05/2020 at 11:58 0 comments

    LEDs come in all manners of sizes, colors and brightness. To be able to choose the most appropriate ones, we need to know what are they going to be used for. For this purpose, we did some market research on UV curing glues. After checking the datasheets of 89 models of adhesives across 4 different companies, we came up with following graph:

    The source of this information can be found in spreadsheet format, here.

    Let’s highlight some important aspects of this dataset:

    • Save for a handful of glues specifically designed to be cured by visible light. All studied adhesives can be cured by a wavelength of 365nm.
    • The large majority of datasheets recommend an irradiance of around 100 mW/cm^2 or less for ideal curing conditions. (Though the documentation can be somewhat ambiguous on the absolute minimum irradiation required to still cure the product).
    • Small portion of glues from Henkel recommend using a secondary wavelength of 250nm to improve curing on surfaces exposed to oxygen. We will not be addressing this, as it would prohibitively increase the cost of the project.

    From this information we can conclude that we should ideally aim for a lamp that emits 100 mW/cm^2 @ 365nm, as this gives the project the best coverage of commercially available glues. Though as we will soon see, it is not trivial to emit light at such high intensity from a battery powered device.

    SELECTING THE LEDS ON MOUSER/DIGIKEY

    It turns out there are not that many high power UV LEDs available in Mouser or Digikey. Even less when you search for ones that:

    • Emit at 365nm
    • Have high power and efficiency.
    • Are inexpensive.
    • Are readily available and well stocked.
    • Have small viewing angles (we need a concentrated beam light to reach those 100mW/cm^2)

    We decided on the IN-C39ATOU2 from Inolux, link to the Mouser listing here.

    Some highlight of the LED are:

    • Forward Voltage: 4.4V
    • Forward Current: 1Amp
    • Radiant Flux: 1600mW
    • Wavelength: 365 – 370 nm
    • Viewing Angle: 30°
    • Size: 4x4mm
    • Cost: 13.62 $ per led

    Note: Yeah, I know that they look really expensive. But the other were not much better. UV LEDs are just really expensive.

    HOW MANY LEDS DO YOU USE ?

    Ideally we don’t want to use more LEDs than absolutely needed, both because of the price, and to save on battery life. Thankfully the datasheet provides us with all the information needed to run a couple of simulations and figure this out. Namely, the total power emitted as light (1.6W) and the radiance pattern, which looks like this:

    Image source: IN-C39ATOU2 datasheet

    No we can program a small script in Python to calculate how this beam pattern would look projected over a surface, at different heights.

    From here we can see that at its peak, 6 LEDs can indeed generate the 100mW/cm^2 we were looking for, even if it just in a small point. Now let’s look at those irradiance patterns a bit more closely:

    At 7cm from the target, the center of the pattern surpasses 100 mW/cm^2, and there is a circle of about 2.4cm in diameter of light above 90 mW/cm^2. Not much in terms of area, but that’s quite an impressive power density.

    Now, if you’re working with glue that cures at lower energy levels and prefer less power over a larger area. At 25cm away, the six LEDs can generate a circle of 14cm in diameter with over 20 mW/cm^2. Which is rather respectable for a handheld battery powered device.


    CONCLUSION

    For a total electrical power consumption of 26.4W and around 81.72$, these LEDs seem like the most sensible choice for the job. They cover both scenario, focused high intensity UV light from up close for those glues that require it. And, wide area low intensity UV light from far away for when area coverage is more important than high intensity.


    EXTRA:  WHY NOT USE STANDARD 5MM UV LEDS ?

    Let’s explore a fair question that might be in your mind after reading this post. If you search on Amazon or Ebay right now for “UV LED”...

    Read more »

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Discussions

John Loefler wrote 07/09/2020 at 22:16 point

The only one I found. In my searches that has more power output is the

NVSU333A (https://www.nichia.co.jp/specification/products/led/NVSU333A-E.pdf)

  Are you sure? yes | no

Said Alvarado Marin wrote 07/14/2020 at 21:58 point

Hi John! I'm glad you liked the LEDs, it took a lot of investigation to find them. :)

The NVSU333A look really impressive, that's a lot of Radiant Flux in such a tiny package. Heat dissipation must be really tricky to manage in such a powerful LED though.

  Are you sure? yes | no

John Loefler wrote 07/07/2020 at 18:54 point

Good Choice on the Inolux LED.  Not only is it better than any lower powered array.  Because it is a single chip the output is a coherent.

  Are you sure? yes | no

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