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This project extends the previous work on creating a prosthetic adaptation for percussion. The focus of this modification is to improve the original design. The primary objective is to develop a prosthetic attachment that can be easily attached and detached independently, while ensuring that the prosthesis is safe, durable, and user-friendly.
We have been assigned to improve a prosthetic arm attachment for a middle school girl who is a bilateral amputee. She currently uses the device to play percussion, but the current attachment point is weak and tends to move. We aim to modify and improve the original design so that it can be easily attached and detached independently and is user–friendly while still providing a firm hold.
We were requested not to meet with the family initially and proceed with the modification first. After the modification was completed, we would then contact the family. We are going off the base line to make an improved adaptation prosthesis that is easier to switch.
Initially, we contacted the previous group that developed the initial prosthesis to understand the design process and background research. We were able to obtain their original design for the drumstick holder and evaluated what strengths their design had. Our focus was to enhance the design by improving the grip, rotational control, and variability of the drumstick, as well as enabling independent attachment and detachment of the prosthesis. With our goals established, we independently researched different methods that would achieve them.
Our research led us to “activity-specific prosthetics,” which are prosthetic attachments designed for a singular purpose, as opposed to more typical and general-purpose prosthetic hands. These are made by a variety of companies, and there seem to be no industry standards for attaching these to users’ arms. We quickly realized that this type of prosthetic design depended strongly on the user’s needs and preferences, so we brainstormed concept designs based on what we knew about the client.
This design concept centers around using a commercial-off-the-shelf quick-release seatpost clamp, as seen on bicycles. On a typical bike, the seatpost shaft sits inside of a slightly larger shaft with a slit cut down its length. When the clamp is tightened, the outer shaft is squeezed onto the inner shaft, providing a frictional clamping force. As the attachment can be freely positioned before the clamp is engaged, this design allows complete rotational control for the user while still providing a strong hold (enough to support the weight of an adult man when used on bikes). Because the clamp is engaged and disengaged with only a single lever, this design should be easy for the client to manipulate without assistance. If the force required to clamp and unclamp proves too strong for the client, it can be easily reduced by extending the length of the lever arm. Pictured below is a typical commercially available seatpost clamp. Note the eccentric cam on the lever arm, which produces the clamping force. Also pictured is a typical outer seatpost shaft. The slit which allows the tube to flex can be seen.
Some activity-specific prostheses are attached to a user’s arm using a simple screw. While this solution neither allows rotational adjustment nor sounds particularly fancy, it is incredibly simple and cost-effective. While we suspected this wouldn’t be chosen, we thought it would be a useful exercise to compare it to the other solutions. If we couldn’t perform better than a screw, we knew we had to go back to the drawing board.
This concept consists of a matching set of magnets embedded in the forward-facing surface of the arm and the base of the attachment. Rotational control is supported by the magnets (the user can choose the rough orientation of the attachment when connecting it to the arm), as well as by flex tubing similar to that seen on TIG welding heads. The tubing would extend from the attachment base to the working end, allowing a few degrees of twist and flex for the user to fine-tune the position beyond what the magnets allow. If the forces of drumming prove too strong for the flex tubing, alternate methods of rotational control might be considered. The hold force provided by the magnets needs to be fine-tuned to provide a strong hold while remaining viable for the client to remove without assistance.
Our decision matrix ultimately led us to select the bike collar concept, only narrowly beating out the Magnet-Based design and the screw, thanks to its relative ease of manufacture, ease of use, and rotational control.
To fix the shafts to the arm and attachment, two metal plates with a threaded hole will be embedded in them during the 3D printing process. The shafts would be threaded and inserted into the threaded holes after the print is completed. A commercial bike collar would then be purchased to connect the arm and attachment. If the threads show a tendency to slip during use, a cotter pin may be added to firmly secure the shaft to the arm.
