Overall specs of the prosthesis
The major difference between the conventional bespoke prosthetic hand and the 3D printed prosthetic hand would be the price and accessibility to the components. By creating the hand using a 3D printer, the manufactures side could reduce the time to produce and deliver, the user would be able to print their desired parts using the 3D file provided by the manufacture by themself. The easier accessibility to the components could not only reduce the cost of manufacturing but also, opens the issue of the bespoke prosthetic where all the parts are handcrafted.
The main material used to build the prosthesis are mostly plastic resin and metals. The benefit of utilizing plastic resin instead of the full metal body like the conventional prosthetics are easily reproducible parts, weight reduction, decrease in stress from breaking due to its cost, resizing to look natural with another hand, and reduction in manufacturing cost. The socket of the hand could be 3D scanned using photogrammetry. This will reduce the hustle of creating a mold of the recipient's amputated arm. The data file could be then sent to the manufacturer which then will be 3D modeled and create data that is printable using a 3D printer.
The hand is actuated using microcomputers (Arduino and Raspberry pi). By utilizing cheap electrical components that could be easily purchased in online shops, the overall price to manufacture the hand could be reduced.
In order to select the mode that the user has desired, users could create their own recognition model on raspberry pi hidden inside the arm using the data fed from 4 EMG sensors. The model created will be used to identify
different modes that the user has pre-trained to select the desired option to actuate the movement on the prosthetic hand.
The major issue when prototyping was the strength of the fingers. In the past prototypes, fingers were actuated using plastic micro servos which have created energy loss, noise, and not enough power.
The solution to the issue was solved by creating a high torque microactuator using a 3D printer. This technology has allowed the hand to stay compact but be able to carry more than the weight of the hand itself.
Currently, majority of the prosthesis utilizes sensors such as pressure sensor, EMG, or a button to execute the functions they prefer to. From the perspective of the builders, this would be not the main issue since
we are too focused on the technology on the prosthesis itself. Although through the feedback of patients for the past prototypes, only providing a button to select options and controlling by adjusting the slight difference
would be a large issue due to the amount of concentration required to get the expected outcome from a sensitive sensor is not their priority when actuating the fingers.
To address this issue, the basic question that had to be solved was "how to provide an option for the user to have an option". This lead to a specific solution of the user being able to create their model which was possible
using AI (for nerds, Tensorflow MLP). The data is read from 4 individual EMG sensors, which could be wireless, from a raspberry pi hidden inside the arm. For more details, I have created a short video of it.
In this prototype, the actuator and the finger are integrated into a single unit, making the finger modular. Its advantage is that the whole finger can be easily replaced in case of failure. For this reason, the wiring was changed to a flex cable instead of soldering on a microcontroller for easy access. This made it possible to create a more compact prosthetic hand than previous versions.
