Simple Prosthetic Gripper DesignCameron Noe/ cnoe1@asu.edu

Collins /Visual Prototyping– ART 494 / Digital Culture / Spring 2014

AbstractThe objective of this project is to create a simple gripping system that employs novel Biomuscle actuators. Nitinol is a shape memory alloy capable of being trained to function as a synthetic muscle actuator. These linear biomimetic actuators, known as Biomuscles, are being developed for use in prosthetic and robotic systems that mimic systems found in nature. Many systems in engineering focus on design based around rotary motion such as the kind found in electric motors or common combustion engines. For this project a crustacean was chosen as the model organism because the exoskeleton and muscle structures of these creatures lend themselves more easily to replication with 3D printing and Biomuscle technology. To bridge the gap from a traditional engineering framework to pure biological replication a prototype gripper was designed to implement and verify the actuators potential and test the validity of an Electromyography (EMG) control scheme.

What is Nitinol?Nitinol is a shape memory alloy. This means that it can be trained to remember a shape at high temperatures and quickly quenched to lock in this shape. Once cooled the nitinol exhibits a large amount of elasticity, and can be bent or contorted at will. Once heated past its transition temperature again however, it will attempt to revert to the shape it was trained into at high temperature.

ResultsBoth the scanning approach and the design approach resulted in printable 3D models. The systems both seem physically sound and ready to progress to the next stage of Biomuscle actuator integration. The EMG control scheme also proved effective allowing the user to control actuator contraction via the contraction of their organic muscles.

Conclusion 3D scanning seems like a feasible way to replicate the complex geometries found in organic systems. In the future, similar methods could be used to replicate other more complex internal systems from medical scans to forego the necessity of external only scanning technology. EMG control seems like a promising avenue of control for a muscle based system short term, however in the long term direct neural integration would be an ideal method for any muscle based system.

Acknowledgements

I would like to thank Dr. LaBelle from the School of Biological and Health Systems Engineering for serving as a mentor to the Biomuscle project. I would also like to thank the other members of the biomuscle team Kaite Conrad, Coleen Fox, Sritej Attaluri , Jonus Reyna, John Ernzen, and John De La Cruz for their continuous efforts on the project. Additional thanks to other lab members Aaron Meidinger, Brittney Haselwood, Chi Lin, and Shannon Brown for their support.

Research Question How can organic systems be accurately replicated and controlled so that they can optimize the use of biomuscle actuators?

Precedents and Prior ResearchBiology follows completely different rules of design than those found in typical engineering practices. Thus when attempting to use synthetic muscles it makes sense to look at existing organic systems that already effectively employ similar muscle groups. Using 3D scanning and printing technology one can not only copy but also alter natural designs for use in engineering design. An advantage of using this approach is that nature generally adds a layer of preexisting optimization in the form of natural selection. Prior research for this project is grounded in the development of lighter more organic prosthetic devices that operate with biomuscle actuators. Development of light- weight muscle actuators would greatly help the field of prosthetics as well as biomimetic robotics.

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ProcessA NextGen 3D scanner was used to gather 3D information from a crab claw. This information was then processed with 3D modeling software packages such a RHINO and Geomagic to render the structure as a 3D printable objet that would preserve the geometry of the original claw. To bridge the gap from traditional engineering design to a biomimetic system a simple light weight gripper was designed in Solidworks to use the muscle actuators. The Solidworks model was built on a Makerbot and the scan generated claw was printed on a Z-corp printer. Additionally an Arduino Uno was adapted into an EMG sensor platform to control the contraction of the muscle actuators. Contraction in the nitinol is temperature based. The materials own electrical resistance is used while passing electrical current through it to generate the necessary heat to initiate a conformational shape change in the alloy leading to contraction.

Nitinol at extended length (No EMG signal)

Nitinol in contracted state with LED indicating EMG signal detected