Biomedical Engineering Reference
In-Depth Information
Figure 7.7
Electrorheological fluid in reference (left) and activated states (right) [20] (© Institute
of Physics and IOP Publishing) (See Plate 15)
These chains alter the ERF viscosity, yield stress, and other properties, allowing it to
change consistency from that of a liquid to something that is viscoelastic, such as a gel,
with response times to changes in electric fields on the order of milliseconds. Figure 7.7
shows the fluid state of an ERF without an applied electric field and the solid-like state
(i.e., when an electric field is applied). Good reviews of the ERF phenomenon and the
theoretical basis for ERF behavior can be found in [21 - 24].
Using rheological fluids does have some disadvantages, however. For example, it is
considered a hazardous substance and the user must avoid direct contact with the fluid
since it contains oxalic acid. Another problem is that because ERFs are suspensions, they
tend to settle out in time. Finally, it is very difficult to get good spatial resolution in any
actuating device.
7.3.3 Electromagnetic Tactile Displays (Shape Display)
This type of tactile display uses linear movements of an electromotor to simulate the
shape. A good example of this category is the work achieved by Wagner
et al
. [25] in
which they used an array of 36 (6
6) servomotors as a shape display. Figure 7.8 shows
the pin array and the servomotors, which are arranged in such a way that, as shown in
this figure, their rotational movements are converted to linear movements of the pins.
Ottermo
et al
. worked on fabricating a shape display using micromotors on the handle
of an endoscopic grasper. The sensor array is 24
×
8 mm and consists of 30 piezoelectric
sensors, while the tactile display comprises 30 micro motors adding up to a total size of
32
×
18
×
45 mm [26, 27].
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