One of the most exciting applications of micro linear actuators is in the production of prosthetics. Over the years, many different prosthetic designs have been created which focus on fulfilling the essential functions associated with the limb it is replacing.
The introduction of the micro linear actuator into the production of research-based and consumer ready prosthetics have increased the overall effectiveness of these products. By imitating the basic range of motion provided by muscle tissue and tendons, linear actuators allow for a system where a robotic prosthetic can be utilized to meet the needs of their users.
But, there are limitations to the application of these components, namely in the natural sensory feedback essential to controlling an organic limb. In a situation where a mechanical system needs to provide the same nuanced articulation as an organic one, there is a need to create drive systems which combine positive aspects of conventional actuator design with additional capacities. These capacities can be linked to the safety and controllability of what can be called compliant structures, which adapt to the situation they are utilized. In this way, the endurance, power, and accuracy of a mechanical system can be combined with the safety and controllability of a natural, organic one.
DARPA (Defense Advanced Research Projects Agency) is committed to developing new technologies which help active military and veterans, while also paving the way for commercial innovation.
To quote from their website:
To cast a javelin into the infinite spaces of the future.” — Franz Liszt
The DARPA HAPTIX program, Hand Proprioception and Touch Interfaces, furthers the DARPA commitment to veteran health by helping to restore full and natural functionality to wounded service members.
The goal of HAPTIX is to create a prosthetic hand system which can move and provide sensations which emulate the natural hand. This centers on the idea of sensory feedback, which allows users to experience and control a prosthetic like never before.
Feedback from nerve cells, associated with kinesthetic responses as well as sensory input such as touch and temperature, are essentially important for many functions. Without this feedback, the prosthetic remains numb to the user, and therefore cannot exert the same functions as a natural hand. Furthermore, the lack of connection to the user impairs the wearer’s willingness to use it. The HAPTIX program intends to create a previously untapped sensory experience that will change how wearers perceive the prosthetic. At the same time, the HAPTIX technology will interface permanently with the peripheral nerves in humans, allowing users to control and sense the prosthetic using natural signaling pathways.
HAPTIX technologies aim to tap directly into the remaining motor and sensory signals of the arm and hand, allowing for a more natural and intuitive control of the complex hand movements. This would allow for more precise movements of the mechanical system, potentially making common tasks more easily accomplished or opening the door to more specialized activities. The addition of sensory feedback in the form of pressure or stress sensors may also further improve functionality by creating a sense of hand posture and grip force.
Functional Neural Interface Lab
Based out of the Case Western Reserve University in Cleveland, researchers working through the HAPTIX program have developed a new system that changes the realms of possibility of myoelectric devices. First off, myoelectrics basically use preexisting signaling pathways to control prosthetics. In the case of the Functional Neural Interface lab, control of the prosthetic activated through the flexing of muscles in the arm which would naturally trigger a response. Implanted electrodes, tapped directly into key nerve locations, ultimately provide the essential stimulation for the actuator control. However, what makes this system so interesting is the reverse feedback—sensory input being fed back to the nerves from the prosthetic.
Recent advances in hardware and software have increased the effectiveness of implants, either in the brain or body, and made it easier to understand and mimic the essential neural code responsible for controlling natural signaling systems. Accurately modeling and imitating this neural code, a series of electrical impulses fed to the nervous system, is essential for conveying information between the brain cells and peripheral nerves throughout the body. Just as these signals drive the actuators of the body, and provide sensory feedback about limp position or exerted force, they are also the key to drive the newest innovations in prosthetics.
Though there are several approaches to design the implanted interface, it is most easily implemented by inserting electrodes directly into muscles or wrapping them around the nerves that control the muscles contractions. On the other hand, the most invasive procedure involves inserting electrodes deep into the nerve itself, requiring less current to activate and making targeting specific groups of nerves more effective. Between these two extremes is a system that encircles the nerve, and places electrical contacts on the surface of the nerve, even allowing for dynamic channel systems which create a network of utilizable nerves. The more channels, the more possible it will be to access small groups of axons and provide a more useful range of sensations.
Current research centers on the development of a robust sensory simulator which can be used to directly interface with peripheral nerves. This system would need to continuously monitor hundreds of position and tactile sensors on the prosthetic and then feed that information back to simulator. The development of a fully implantable simulation system, paired with a coupled HAPTIX prosthetic, would allow users to interact with their environment in a way that was never before possible.
| *NOTE* Morai Motion has no affiliations with any of the above mentioned companies or projects. The article is intended solely as a point of interest and information regarding use of technology for human improvement and enhancement using micro linear actuators in the production of prosthetics. |