ECE 110/120 Honors Lab Section : An Extra Set of Hands

Introduction: 

• This project will be to create prosthetic appendages that can mimic or replicate the function of human arms and hands. These mechanical appendages will be operated by accelerometers that will be strapped to the top of a user’s boots. The accelerometers will send signals directly to servo motors which will control the position of the arms by pulling strings attached to individual joints. These arms will be supported by an upper body harness where the bread board housed and the wires organized. A force sensor will be located in the palm of each hand, which will react to the weight of the object placed in the hands. The weight of the object will act as an input to decide the grip of the fingers. The end goals for this project are for each arm to successfully grab and lift objects at least ten pounds in weight off of the floor. 
• My project’s purpose will be to provide an affordable and high functioning prosthesis alternative compared to other models. Where many models are designed solely for amputees, I want my project to be inclusive to all who are interested in it. To help with inclusive I will design the functions to have a quick and understandable user interface, which can be utilized by anyone. Based on the research I have done so far, a popular trend in self made prosthesis is to control the limbs with a microcontroller, rather than allowing the sensors to directly determine the movement. While I cannot yet say whether one will be necessary, I plan to complete this project by relying on one as scarcely as possible. 
• All the projects I have viewed so far are controlled with either flex sensors , voice commands, or in rare cases brain waves for ultra precise control, by keeping my sensor systems basic I hope to avoid the same dependency. As I progress with my project, I will aim to hit 3 distinct thresholds before continuing on with the design. This will start at achieving near full range of motion with the arms, having successfully accomplished this, the next target will be implementing the grip sensor, following this will be precise movements of the hands and fingers. If all three of these goals are achieved I will return to continually adjust the cosmetics of the system. 

Background Research:

• While brainstorming for this project I considered several different unique ideas. To shorten a long list, I considered converting an acoustic to an electric guitar, a droid to assist me when I solder wires, and a skate board that specifically is designed for heavy snow. After considering the chance I was given with this project, and how best to take advantage of it, I decided that my project should be something I can apply to my interests later in life. I am particularly interested in a career in mechatronics, which designing these prosthesis will give me a great chance to immerse in at my own pace. I hope to later apply what I learn on this project to a career in prosthesis or robotics.
• The preliminary findings of my research have lead me to several conclusions that have held decide the course I want to take. The first of these is in regard to the material that my system will need to be made of. While aluminum would be an ideal fit based on its weight and relative strength, it is very costly to manufacture and does not leave room for error in designs. Wood could also be a beneficial choice for material, but it has the potential to be even more costly that aluminum to work with, not to mention the testing that would be required to determine the ideal species of wood. With those two options eliminated I am left with plastic as the only choice. Thankfully this is nearly an ideal material, as through 3D printing I can choose the density and strength of my material. While undesirable, errors could be made more easily as PLA plastic is flexible and cheap allowing for modification of existing parts, or the ability to recreate them and solving the error. This appears not only to be the smartest choice of material, but also the most popular, presumably for the same reasons. I am considering using aluminum as a bracing material to be used in the harness, or as support rods in the limbs, as it is much stronger than PLA and will be able to distribute weight more safely.   
• While researching the various sensors that could be used to drive the functions of the arms, I encountered numerous solutions that all have potential to work exceptionally well. Of the ones I expected were flex sensors, and programmable microcontrollers, but surprisingly I found several models utilizing voice control and in rare occasions brain waves. While I would like to have the ease of relying on the microcontrollers, it is a short cut I want to avoid as I don't believe it is truly necessary for  my prosthesis to function. By utilizing some of these devices, the designers sacrificed the fluidity of their projects as interacting with programmed functions interferes with the fluidity of using the prosthetic. By choosing to use accelerometers and force sensors, I believe that one can learn to use instructively without distracting from their routines.   
• Differing views on the mechanics of the system were scarce during my research. The most common method of translating the electrical signals into motion was done by thin strings attached to servo motors. This was often the case as servos are able to exert large amounts of torque to the systems they operate in. While I would prefer to pursue a path that is not commonly used, a new use of mechanics is not the intention of the project, and I have not been able to determine a better solution that what has come before.   

     Block Diagram:

System Overview:

• The current plan for how I will build my circuit relies on the two sensors, and various checkpoints along the way. The first decision my circuit will make is if it is ready to run. This will be done by inserting a kill key just before the power source connects to the circuit. This will act as a safe guard against any power flow when the system is not it use. After this comes back clear, data in the form of electric waves from the sensors will be transmitted to their respective servo systems, and will act independently from each other. In the case of the arm movement, it will be required to pass another kill key test as the user may wish to lock the arms in place. If the arms are unrestricted by user preference and range, they will react to the position of the accelerometer and move accordingly. The force sensor will act similarly, but instead of checking for the ability to move, they will sense if the weight they are asked to hold, is to heavy for the system. If this is the case they will notify the user, and remained open palmed. 

Parts:

Possible Challenges: 

With what I know right now there are a few issues I expect to complicate my completion of the project.

•  The first of these is wire management. Since the intention is to keep my project as analog as possible, this will lead to the need of extremely long wires to reach from the accelerometers to the housing unit in the harness. A concern I have right now will be managing these wires without restricting the movement of a user. If I allow these wires to much freedom there is the possibility of tangling and catching on the users surroundings. 
• I can easily foresee is acquiring servo motors that are able to successfully lift the 10 lbs weight I have determined to be my goal. While the servos will need to be large to provided the needed strength, I do not want them to be so large, as to be visible in the harness. There is cost of stronger servos which will rise as their power and size does.
• While finding a power source is not  a concern I have, finding one that poses as little risk to the user and circuit might be difficult as I search and shop for parts. As a user will be wearing my device on their back, it is important that I keep their safety in mind throughout the whole process.
• My experience with digital sensors is limited, bridging the gap between interpreting information through a micro controller to interpreting it through an analog circuit may be the most difficult aspect of the project for me personally. 

References:  

• BGR India. (2015). Indian-origin teen Nilay Mehta creates low-cost robotic arm | BGR India. [online] Available at: https://www.bgr.in/news/indian-origin-teen-nilay-mehta-creates-low-cost-robotic-arm-360476/ [Accessed 15 Feb. 2020].
• Jeffrey, C. (2019). Open Bionics' 3D-printed 'Hero Arm' is now available in the US. [online] TechSpot. Available at: https://www.techspot.com/news/79515-open-bionics-3d-printed-hero-arm-now-available.html [Accessed 15 Feb. 2020].
  
• Donaldson, W. (n.d.). [online] Instructables.com. Available at: https://www.instructables.com/id/Robotic-Arm-3D-Printed-DIY-Initial-Prosthetic-Prot/ [Accessed 15 Feb. 2020].
  
• Nathan, S. (n.d.). The Arduino Prosthesis Using the Neurosky Mindwave | LEARN.PARALLAX.COM. [online] Learn.parallax.com. Available at: http://learn.parallax.com/educators/inspiration/arduino-prosthesis-using-neurosky-mindwave [Accessed 15 Feb. 2020].
  
• Instructables.com. (n.d.). Arduino Powered Bionic Arm. [online] Available at: https://www.instructables.com/id/Arduino-Powered-Bionic-Arm/ [Accessed 15 Feb. 2020].