Prosthetic Arm Force Reducer Team 1 – Halliday's ... - Ohio University

hook allows the customer to operate in the full strength position only when necessary. Customer
interaction has confirmed that this full strength setting offers more grip force than his currently
modified prosthetic. Additionally, the customer can use half of the grip force and, therefore,
have only half of the input force by a simple adjustment of a lever. Immediate effects of the
upgrade to springs are that the user will be able to perform a wider variety of tasks with the
increased grip force and also use the hook at half power, similar to a standard existing one-load
hook. Long term effects could include fatigue and increased stress on the user’s body if the hook
is used at full load fairly often and possibly an increase in the stresses in the entire prosthetic
resulting in shorter product life due to fatigue.
The mechanical advantage system offers relief for this. The ideal case for this system would
give the user a 2:1 advantage in the input force required to open the spring hook. For example:
Assume the original spring at the high setting required 35 lbs. Now, with the mechanical
advantage pulley, it should ideally only require 17.5 lbs to open the hook at full load. The
impact of this system to the user would be a drastic reduction of the input force required for both
settings on the two-load hook. Our design reduces the input force required by the user by 47%
from 18 lbs to 9.5 lbs or about a 1.9:1 advantage.
The negative impacts discussed for the move to the Otto Bock hook and its stiffer springs would
be reduced significantly, because even with an increase in grip force, the user would be able to
exert less force than in an unmodified system. With respect to the mechanical advantage system,
the user would theoretically have to pull their cable twice as far as was previously required to
fully open the hook in order to balance the energy and forces for a 2:1 mechanical advantage. It
currently takes about 1.75 inches of cable travel to fully open the customer’s hook. The Otto
Bock hook, however, does not open as wide as the customer’s hook. This reduces functionality
somewhat, but is beneficial in that he will only have to pull the cable ~2.75” inches, instead of
the 3.5 inches it would take to fully open his current hook.
Short term effects of a mechanical advantage system upgrade would be an increase in user
comfort due to the ease in which he or she can use their prosthesis. It would allow for the
immediate implementation of an increased-strength two-load hook without increasing the force
needed to operate such a device.
Long term effects are an increased life for the cable operating the pulley, and an increase in the
workload the user could accomplish. Some possible negative long term effects could include
shorter lifespan of the cable post and the cable connecting it to the pulley since they would be
experiencing an increase in tension from the springs. Also, there is a possibility of eventual back
and shoulder injuries from prolonged use, though this fact exists with all current prosthetic hook
designs.
The overall impact of the production of this system on the environment or society would not be
very significant. As currently designed, this upgrade kit uses mostly pre-produced parts that
need little machining. Most of the work required is in assembly and can be done by a few
trained operators. The greatest impact or effect of the combined upgrade system would be to the
life of the customer who would be using this system on a daily basis, allowing him or her wider
range of tasks that they can complete and decreasing the wear on his or her body.
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