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Multifunctional Actuators for Assistive Knee Braces
Swing
extension
Swing
flexion
Preswing
Stance
extension
Stance
flexion
FIGURE 13.2
Gait cycle and walking states for normal walking (Wikenfeld and Herr 2003).
Belts
Upper braces
Gearbox
Gears
Multifunctional
actuator
Lower braces
Belts
FIGURE 13.3
Configuration of the assistive knee brace with the actuator.
Thus, the multifunctional actuator developed meets any motion required of
an assistive knee brace.
The configuration of the knee brace that utilizes the multifunctional actuator is shown in Figure  13.3, where the multifunctional actuator provides
active and semi-active torque to help the wearer achieve better mobility.
13.2.1 Motor Design
The motor is designed based on conventional electric motors. Considering
the advantages of simple construction and maintenance, as well as high efficiency and torque per volume, a brushless permanent magnet (BLPM) DC
motor was modified for the motor.
Generally, BLPM DC motors are constructed in three basic physical configurations as shown in Figure 13.4, in the form of an interior rotor, exterior
rotor, or axial rotor. The interior rotor configuration is an appropriate choice
because high torque with low speed is needed. Such a configuration can be
made with a large hole through the center of the rotor, which provides valuable space for other parts of the mechanism (Hendershot and Miller 1994).