Rotary Actuator; Figure 4.2.5 Construction Of The Actuator - Fujitsu M2361A Customer Engineering Manual

4.2.3 Rotary actuator
The drive shaft of the head-arm assembly in the DE is coupled directly to a
bobbin supporting base to be driven by the rotary actuator outside the DE. A
ferrofluidic seal is utilized to separate inside and outside the DE. Two
coil-bobbins are attached to the bobbin supporting base, and two magnetic
circuits are provided to supply torque to the coil bobbins, moving the head-arm
assembly to the desired cylinder within a short access time.
Figure 4.2.5 Construction of the actuator
(1) Magnetic circuit
The pair of magnetic circuits are constructed symmetrically as shown in
Figure 4.2.6. Each circuit incorporates four permanent magnets (rare
earth magnets) with two magnetic gaps in between. Each magnetic gap
contains a uniformly spread magnetic field. The coil bobbin is inserted
in it and generates torque proportional to the current in the coil and the
intensity of the magnetic field. This torque is sufficient to move the
head-arm assembly at the specified speed.
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