A team of Brazilian researchers delve into 3D printed prosthetics that are affordable and can be programed, with 3D printing and materials becoming more available worldwide scientist are making stride with custom medical devices.
The goal of this study was to make robotic prosthetic affordable while improving their functionality for individuals with disabilities. Using 3D printing the team wants to implement EMG sensors, and strain gauge force sensors, to help with social interaction and dexterity to improve the overall quality of life. The structure of the prosthetic is meant to mimic the structure of the human hand skeleton with 27 bones.
“Thus, at the end of the modeling of the structures, the equivalent of 37 pieces was reached, all of them structured so that it was possible to pass internal cables to perform the movement of the fingers during an action.”
The hand uses cables of nylon monofilament as “muscles” to pull the fingers for gripping. The hand overall is made from PLA and uses high torque 13 kg / cm servo motors to move the digits. The palm had a 15mm wide force sensor with a measuring range between 100 grams to approximately 10kg
“The purpose of this sensor was to prevent structures from being detected during the closing movement of the fingers, and during contact, it prevents the fingers from closing irregularly, causing damage to the structure,” stated the researchers. “The sensor has a circular shape with approximately 10 cm in diameter and is located on the palm of the prosthesis.”
EMG sensors also presented limitations, mainly in measuring only one muscle EMG stimulus, noise, and setpoint adjustments—leading the researchers to modify the position of the target musculature.
“The results showed that, based on the implementations performed, the sensory application proved to be satisfactory in view that the results measured between the prosthesis and the target musculature, were measured and converted into movements for the equipment,” stated the researchers.
“Thus, the force sensor was able to stop the movement, preventing the fingers from closing in such a way as to damage the joint structure of the prosthesis. The structures printed in PLA filament are also sufficiently controlled during the assembly steps, considering that they were able to withstand a force exerted by the servo motor equivalent to 13kg in the process of pressing the fingers.”
After reviewing the project, the team says the ‘final acquisition value of the project’ was around R$ 2,000.00 ($365US).
“Aiming at future studies involving the improvement project of mechanical prostheses, sensors that may simulate the touch of a surface similar to human skin may be provided, as well as the insertion of new force and EMG sensors to better treat the stimulus signals dissipated in the muscle ventricle. In this way, the project should pass through new structural dimensions such as modeling and printing of new parts that can reduce limitations of the current structure, for example, the non-displacement of the fingers on the Cartesian x axis,” concluded the researchers.
“As a means of providing greater flexibility through the printed structures of the prostheses, the use of filaments such as TPU (polyurethane thermoplastic), total or partial, is estimated for items that may require multidirectional behaviors, such as prerotation of the fingers. The servo motors used in the arm structure take up too much space to the real needs, aiming at the use for people with only hand amputations, it will be necessary to use smaller motors, and also the space needed for their allocation in the prosthesis structure.”
O’Neal, Bridget. “Brazil: 3D Printing an Affordable & Programmable Robotic Prosthetic – 3DPrint.Com: The Voice of 3D Printing / Additive Manufacturing.” 3DPrint.Com | The Voice of 3D Printing / Additive Manufacturing, 19 May 2020, 3dprint.com/266420/brazil-3d-printing-affordable-programmable-robotic-prosthetic/.