Iterative Design Diagram / Created by: Sky Sze, Faheem Karim, Xuecen Wang, Brian Ferreira
The design process of our prosthetic follows an iterative methodology. The objective of our design was to design an upper limb prosthetic that was capable of replicating the complex motions that are characteristic in the game of volleyball. As such we began to determine various design criteria and constraints that we may face later in the design process. Our requirements focused mainly on the processing capability and mechanical functionality of our prosthetic. We also came to the conclusion that “phantom” limb pain may continue to be a persisting issue associated with our design, as current treatments and research do not point towards a sure-fire remedy towards the pain experienced by amputees.
Once we have adequately defined our criteria and constraints, we can continue on to devising solutions as well as alternatives to our original design. Our primary design incorporates titanium and 3D printing and modeling for the structure of the prosthesis. In addition, we continued with a multi-channel EMG electrode placement in order to receive the signals from the residual limb. The alternative solutions of our design can be alterations to each component of the original design such as change of battery or biomaterial. Possible alternative solutions are elaborated further in detail in the paper.
Once we have selected a design, we will continue to create a prototype using the methods we have mentioned earlier in the design criteria such as 3D Printing and Modelling. Our prototype well then be subjected to various mechanical and user interface testing. The primary objective of these tests is to ensure our prosthesis can withstand the strain associated with volleyball as well as its capability to complete common movements such as grasping an object. These tests will be further elaborated in the paper.
The results of our test will determine the direction of our design process. In the case that our original design process fails, we will look towards our devised alternative solutions and choose a design that we believe is best suited for the tasks that the original design failed to do. We will continue this cycle until we have exhausted alternative solutions and will have to redefine our requirements and constraints, while creating new original solutions as well as alternative. However, if our design is able to pass all the testing we will do and if we are confident that it is capable in fulfilling our objective, we can integrate our prosthesis design into the market and finalize our design process.
Testing
As a whole testing will be comprised of several stages, where it first be mechanically tested for its speed of the signals and the prothesis itself, strength of the movements, reliability, and battery life. It will then be tested on human subjects for its biocompatibility and user interface. It can further be tested with a physical demo volleyball for its usage.
When dealing with the prosthesis itself, mechanically testing of the prototype prosthesis utilizes the Box and Blocks Test (BBT) and the Southampton Hand Assessment Procedure (SHAP) test [19, 20]. The BBT test has 25mm wooden square cubes with a container that is cut into two areas by a wall in the middle. The user with prosthesis needs to transport as many cubes as possible from one side to the other. The score is recorded based on how many cubes are successfully transferred within 1 minute. The SNAP test consists of two parts. The first part requires the user to move objects with variable shapes and weights while in the second part the user has to complete some daily living activities to be assessed. The purpose of the SNAP test measures the ability of the user on performing different grasping tasks.
Alternatives
In order to maximize the potential of our prosthesis design, we must be able to adapt to any obstacles we may come across when testing our prosthesis prototype. As such we must devise alternatives to each aspect of our design in case the original plan fails.
In the case that our multi-channel detection system does not demonstrate adequate levels of signaling, then extraneural or intraneural peripheral nerve electrodes can be used. Although these are more invasive, peripheral nerve electrodes provide similar accuracy, if not more, and precise muscle control and movement due to its ability to use transected nerves. This will also help make each prosthesis more customized for the user.
If during testing the titanium base of the prothesis cannot withstand the activity, the material’s thickness can be increased, reinforcements with the metals or carbon fiber can be added as well. If this does not give back positive results, the material of the forearm can be change altogether. For instance, although the usage of carbon fiber would be expensive, the upper-limb prosthesis will obtain the highest level of durability and lightweight attainable. Another option could be the use of polymers since it’s inexpensive, durable, and easy to replace.
If fingers become problematic, a single combined palm with extra padding more akin to a flipper can be made. This design will have less intricate moving parts increasing its durability but will have less articulation in how the ball will be handled and will likely result in loss of accuracy.
If the electronics do not withstand the stress of being hit by the volleyball, more material can be added to absorb the shock or disperse the force more evenly across the prothesis.
In the scenario that the lithium iron phosphate battery is not capable of outputting a sufficient level of energy for the prosthesis, we can employ other types of batteries that have high efficiency. For example, a lithium ion polymer cell can release higher energy levels per battery weight, a priority during intense periods of volleyball playing. The size of our battery may also pose a problem and make our prosthesis heavy, as such a more compact battery can be used to reduce the weight and size of the prothesis.