Design & Engineering Goals:
- < 10$ price of each Braille Cell
- <1W Power consumption
- Standard Braille sizing
- Scalable to multi-row braille Display
- Ease of Manufacturing & Assembly
- 8 Dot Braille
This design in principle works like a previous design using cam actuation, by replacing the vibration motor with a solenoid that causes an eccentric cam that is embedded with a rare-earth magnet to rotate, and in turn, lift a braille pin.
Refer to the Project logs for a full table of references.
An electromechanical, electromagnet-based braille display that can represent braille characters. The key principle is a cam actuator, consisting of an eccentric cam that has a rare-earth magnet embedded into it which is rotated to two stable positions by the action of an electromagnetic that changes its polarity. The rotation of the eccentric cam causes a braille dot to be lifted up or taken down.
The cam rotates slightly more than 180° and is stopped against the wall of the enclosure (Upper Cell). Once the Braille pin is lifted, the weight of a finger on the pin(while reading braille) cannot back drive the cam. This not only satisfies the need for protrusion force of the braille pin but also that the electromagnet need not be powered once the pin has been lifted resulting in lower power consumption.
Prototyping is done using a high-resolution SLA 3D Printer as there are many thin-walled sections.
PR4 REsin on a 3D Systems Figure4 machine is being used for its ability to achieve 0.2mm wall thickness.
To meet the cost goals of the project, the braille cells will be injection molded in POM after the validation stage. The design has already been optimized for injection molding.
The micro 1mm x 0.5mm NdFeB magnet is what makes this project possible, and would be impossible without the availability of such tiny magnets. Luckily there are now a handful of vendors around the world keeping these in stock as they are also used for things like jewelry clasps on thin bracelets, Kingdom Death miniatures, super thing Games Workshop miniatures, and more.
The electromagnets will be constructed with 40-micron enamel-insulated copper wire with a soft iron core. A winding jig will be created to help wind the could around lengths on 0.6mm Soft Iron wire.
The electronic circuit will be heavily inspired by the workings of Flip-Dot displays. Instead of discrete drivers for each braille cell, the same driver will actuate pins of a full braille display with multiple braille cells using a multiplexer since a braille pin doesn't need to be kept powered on once actuated.
Failure mode and mitigation:
The biggest problem expected with the design would be the interaction of all the magnets in a single braille cell with each other, which would prevent the braille cell from functioning appropriately.
To mitigate against this:
- The magnet power could be varied (with controlled heating?)
- Thin steel sheets could be introduced in between the cavities of the "Upper Cell" to shield against the magnetic fields of the individual magnets
- Using plastic material during the 3D Printing or Injection molding process that contains iron particles that would dampen the magnetic field of the magnets.
- Using Metal Injection Molding(MIM) to produce the "Upper Cell".
- Electroplating a thin layer of NIckel (which is ferromagnetic) over the "Upper Cell"