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Biologically Inspired Robotics
Figure 13.16, in the range of 0.5 to 2.5 A, the output torque was approximately linear with respect to the applied current. Therefore, the model of
the brake function can be expressed as a first-order single-input, single-output linear plant.
The response of the clutch function was investigated. Figure 13.17 shows
the response of the clutch/brake under a pulse signal. The response time
was about 0.1 second, compared with the reaction time of an average person
(0.15–0.4 seconds), so it is capable of stopping the torque transfer from the
motor to the assistive knee brace in case of emergency.
Motor braking is an issue for motor control. The commonly used methods for motor braking consume large amounts of power and can damage
the device with prolonged usage. For normal walking, the knee power is
mainly passive and usually occurs during the bending of the knee joint. As
discussed above, with MR fluids, output torque in the brake function of the
actuator is approximately proportional to the current applied to the inner
coil. By adjusting the current, the braking torque control is easy to implement. Experiments on torque tracking of the brake function were conducted,
and the results are shown in Figure 13.18. It can be seen that the actuator can
track the reference well in the brake function.
13.6 Conclusion
In this research, an MR fluids-based multifunctional actuator for assistive knee braces was designed. To decrease the dimension of the actuation device while enhancing its performance, a motor and MR fluids were
integrated into a single device. By applying current on different coils on
each part, the actuator has multiple functions as a motor, clutch, and brake.
Design details of the motor and clutch/brake were considered. The motor
was designed based on an interior rotor BLPM DC motor, and the clutch/
brake was in the form of input–output plates. Possible combinations of
these two parts were discussed. Because the actuator was composed of permanent magnets and MR fluids, the magnetic interaction force, influence
of the permanent magnet on MR fluids, and magnetic flux distribution
were analyzed using FEM. Modeling of the actuator for different functions
was developed. A prototype was fabricated and tested, and characteristics
of each function were investigated. Torque tracking in the brake function
was investigated. Although the measured torque was not high, by adding transmission mechanisms, the torque can be increased while the speed
is reduced. Therefore, the new multifunctional actuator is promising for
assistive knee braces.
Biologically Inspired Robotics
Figure 13.16, in the range of 0.5 to 2.5 A, the output torque was approximately linear with respect to the applied current. Therefore, the model of
the brake function can be expressed as a first-order single-input, single-output linear plant.
The response of the clutch function was investigated. Figure 13.17 shows
the response of the clutch/brake under a pulse signal. The response time
was about 0.1 second, compared with the reaction time of an average person
(0.15–0.4 seconds), so it is capable of stopping the torque transfer from the
motor to the assistive knee brace in case of emergency.
Motor braking is an issue for motor control. The commonly used methods for motor braking consume large amounts of power and can damage
the device with prolonged usage. For normal walking, the knee power is
mainly passive and usually occurs during the bending of the knee joint. As
discussed above, with MR fluids, output torque in the brake function of the
actuator is approximately proportional to the current applied to the inner
coil. By adjusting the current, the braking torque control is easy to implement. Experiments on torque tracking of the brake function were conducted,
and the results are shown in Figure 13.18. It can be seen that the actuator can
track the reference well in the brake function.
13.6 Conclusion
In this research, an MR fluids-based multifunctional actuator for assistive knee braces was designed. To decrease the dimension of the actuation device while enhancing its performance, a motor and MR fluids were
integrated into a single device. By applying current on different coils on
each part, the actuator has multiple functions as a motor, clutch, and brake.
Design details of the motor and clutch/brake were considered. The motor
was designed based on an interior rotor BLPM DC motor, and the clutch/
brake was in the form of input–output plates. Possible combinations of
these two parts were discussed. Because the actuator was composed of permanent magnets and MR fluids, the magnetic interaction force, influence
of the permanent magnet on MR fluids, and magnetic flux distribution
were analyzed using FEM. Modeling of the actuator for different functions
was developed. A prototype was fabricated and tested, and characteristics
of each function were investigated. Torque tracking in the brake function
was investigated. Although the measured torque was not high, by adding transmission mechanisms, the torque can be increased while the speed
is reduced. Therefore, the new multifunctional actuator is promising for
assistive knee braces.