Aug 14, 2018 | By Thomas

3D printing does great things in a lot of areas, but one of the most directly beneficial uses for the technology is prosthetics. All around the world, organizations like e-NABLE and Open Bionics are dramatically cutting the cost of prosthetic limbs for those in need. Traditional myoelectric prosthetic hands which are controlled via electromyographic (EMG) signals generated in skeletal muscles, require the user to concentrate on the task of grasping to position and orientate the prosthesis to grip objects. Surveys have shown that myolectric prosthetic wearers wish to reduce the visual attention necessary to grasp objects with their prosthetic hands.

For that reason, researchers from the Karlsruhe Institute of Technology (KIT) in Germany have developed an advanced five-finger 3D printed prosthetic that aims to reduce the cognitive burden of the user through intelligent mechanisms. Their 3D printed hand prosthesis integrates sensors, an advanced embedded system, an RGB camera in the base of the palm and a colour display in the back of the hand to autonomously grasp objects.

“In terms of mechanical design an adaptive, under-actuated mechanism is used to allow the fingers to wrap around arbitrarily shaped objects,” the researchers explain. “The sensor system includes position sensors in the two motors and an RGB camera for vision-based grasping. The on-board embedded system provides the possibility to integrate proprioceptive sensor information, visual information, user feedback and status information via Bluetooth.”

According to researchers, the proposed hand prosthesis is the first device which integrates a camera in the palm. To ensure human-like appearance the complete hardware including motors, mechanisms, embedded system, sensors, user feedback and user interface is integrated into the palm of an average male hand. The KIT UPro Hand is fully actuatable and controllable as standalone unit without the need for any external computing resources.

The prosthetic exterior is 3D printed by selective laser sintering using PA2200 – one of the most commonly used materials in professional 3D printing of functional prototypes. According to the researchers, 3D printing was chosen as a method of manufacture in order to allow personalized production for the wearer using their 3D printed hand. The fingers are 3D printed from PA2200 to match the strength and visual appearance of the palm. All four fingers are simultaneously driven via a force-distributing transmission based on the TUAT/Karlsruhe mechanism; and the thumb is actuated by a second motor. The structure of the mechanism allows the fingers to naturally shape around objects.

“The tendons pass through PTFE tubes inserted into the 3D-printed material in order to reduce friction,” the researchers write. “Additionally all active joints and deflection pulleys include ball bearings. Custom made springs in every joint ensure the passive reopening of the fingers. By defining a higher pretension in the distal joints, we strive for a human-like closing order of the finger segments with the proximal joints closing earlier.”

The researchers conducted several tests in which the 3D printed hand was used to hold household items of different shapes.

"Our control allows hand preshaping in terms of hand aperture and independent timing of thumb and finger closure. By these means, 85.2% of the remaining 60 objects can be grasped successfully from a flat surface, scoring 193 of the total 230 points." Failed grasps mainly occurred when trying to lift very thin objects like credit cards.

“Despite the high degree of integration in mechanics and embedded system, our approach is limited in the amount of sensorization restricting the application of sophisticated control schemes as proposed with external sensor settings,” the researchers conclude. “Notwithstanding we see the integration of a more thorough multi-modal sensor system as well as its use in semiautonomous control schemes as a promising future research topic. Based on the developed embedded system we therefore plan to extend our work towards a stand-alone prosthesis offering the amount of intelligent grasping support possible with the integrated computing power.”



Posted in 3D Printing Application



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