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

Since the torques of the both the rubber band (Tr) and the User (Tc) can be determined easily by
using Figure 6, the following fraction can be utilized to monitor the user’s capability to open the
hook.
(Capability Index)
By plotting the Capability Index for the hook’s entire range of angular motion, the relative ease
which the user will experience while opening the hook (assuming they apply full force for the
entire travel of the hook) can be observed. This is shown in Figure 6.1.8.
The plot labeled “GOOD” indicates that the user is capable of opening the hook throughout its
entire range of motion. The ease of opening, however, diminishes as the springs/rubber bands
are stretched increasingly. The plot labeled “BAD” shows that at some intermediate Ѳ, the
torque input from the user becomes equivalent to the torque produced by the stretched
springs/rubber bands. Since the user’s input force is assumed to be maximum, the user is not
capable of opening the hooks beyond this point.
UDetermining Minimum Opening Force:
Figure 6.1.8 – Capability Index Plots
It may also be of interest to find what minimum amount of user force (Fcm) is needed to open
the hooks to some angle Ѳ. This can be done easily, using the equations derived from the prior
sections.
(13)
(14)
(15)
(16)
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