Biomedical Engineering Reference
In-Depth Information
Figure 11.17
Measured and calculated signals plotted in real time
selected to be simulated by the actuator. The strain - stress relations for these materials
are shown in Figure 11.19.
To compare the performance of the proposed tactile display, the force - position rela-
tion for each simulated material was saved, plotted, and compared to the force - position
relation of the material. Each curve can be divided into two separate phases: loading and
unloading. The loading phase starts when the finger makes contact with the shaft and
applies force. As soon as the force is removed, the unloading phase starts.
The speed with which the material returns to its initial form during the unloading phase
is dependent upon its composite structure and is, in any event, slower for softer materials.
Figure 11.20 shows both phases in A2 ( 3 / 4 inch thick) and also the fact that, during the
loading phase, a small error exists between the simulated curve and the real curve. An
attempt was made to minimize the error by selecting an optimum controller although the
error, as it transpired, was larger in the unloading phase, which did not, however, distort
the perception of softness. The unloading phase, both in the original elastomer and linear
actuator, started when the finger separated from the surface of the object, and from this
it was established that the speed of unloading did not affect the sense of touch.
11.9 Results and Discussion
Figures 11.21 - 11.23 show the loading and unloading phases for three other elastomers
(EVA
1 / 2 inch, ICF400 1 inch, and B1
3 / 4 inch).
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