Biomedical Engineering Reference
In-Depth Information
FIGURE 8-33
Structure of a linear
motor to drive a TAH
[Adapted from
(Yamada, Mizuno
et al., 1998).]
FIGURE 8-34
Measured
characteristics of the
linear motor based
TAH drive. (a) Static
thrust as a function
of excitation current.
(b) Dynamic thrust
as a function of the
flow velocity.
[Adapted from
(Yamada, Mizuno
et al., 1998).]
Each stator contains 16 teeth with a width of 0.32 mm and a slot width of 0.48 mm, making
the total pitch
τ
=
0
.
8 mm. The length of the tooth is 56 mm. The mover tooth pitch is
the same as that of the stators and is separated from them by a 40
m gap. The drive coils
are each wound with 110 turns and are supplied with an excitation current of 1.4 A.
A linear displacement sensor, as discussed in Chapter 3, comprises four magnetore-
sistive (MR) elements and a magnetic grating embedded within the linear bearing. These
together generate a sinusoidal output voltage with a wavelength of 0.8 mm.
A static thrust of just over 100 N was achieved for an excitation current of 1.4 A, but
this reduced with mover velocity, as shown in Figure 8-34.
A simpler mechanism is described in Fukui, Funakubo et al. (2004). In this design a
moving magnet linear oscillator actuator (LOA) uses conventional voice-coil technology
powered by an alternating current (AC) signal to drive pusher plates directly, as shown in
Figure 8-35.
The housing is made from epoxy using a rapid-prototyping machine, and the di-
aphragm is made from segmented polyurethane from PTG medical Co. and formed using
a dipping method. All of the blood-contact area within the housing is coated with the
same material. The diaphragm, pusher plate, linear guide, and actuator are integrated into
a single unit. A Hall effect device is set into the actuator housing to detect the displacement
of the mover. A pair of Bjork-Shiley tilting-disk valves is mounted on the inlet and outlet
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