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Multifunctional Actuators for Assistive Knee Braces
Generally, actuation devices in assistive knee braces can be classified as
active and semi-active actuators. The most widely used active actuators are
electric DC motors in rotary or linear forms. In addition to electric motors,
hydraulic and pneumatic actuators are other active actuators used in assistive knee braces and exoskeletons.
For active actuators, especially for electric DC motors, brake function requires
a large amount of power to maintain any posture and might cause safety problems. Some researchers have adopted smart fluids in actuation mechanisms;
for instance, a rehabilitative knee orthosis equipped with electrorheological
(ER) fluids-based actuators (Nikitczuk, Weinberg, and Mavroidis 2005). An
orthopedic active knee brace using a magnetorheological (MR) fluids-based
shear damper was developed to make the knee brace have controllable resistance (Ahmadkhanlou, Zite, and Washington 2007). All of the knee braces
developed using smart fluids provide controllable torque by passive and
semi-active means while consuming little power. Furthermore, according to
clinical gait analysis (CGA), the knee joint dissipates power during walking
(Zoss and Kazerooni 2006). Hence, the knee joint dynamics could be closely
matched by a controlled energy-dissipative device; for example, smart fluidsbased actuators. However, in some situations, such as going upstairs or stepping over obstacles, such knee braces do not help in active ways.
To combine the advantages of active and semi-active actuation devices,
like electric motors and smart fluids-based actuators, a hybrid assistive
knee brace that integrates an MR actuator with an electric motor was developed (J. Z. Chen and Liao 2010). The MR actuator can function as a brake
when adjustable torque is preferred and requires low power consumption
or it can work as a clutch to transfer torque from the motor to the brace.
With adaptive control, the actuation system worked well and could provide
the desired torque with better safety and energy efficiency. However, the
actuator seemed a bit bulky to be used on the human body and could not
fulfill the tasks of bidirectional rotation. Therefore, designing a more compact, multifunctional actuator is desired for assistive knee braces.
The objective of this research is to develop a novel actuator with multiple
functions such as motor, clutch, and brake for assistive knee braces. Utilizing
MR fluids, the actuator provides torque safely as a motor and clutch and produces controllable torque with little power consumption for braking. Moreover,
the braking torque control of the actuator could be easily implemented.
13.2 Design of Multifunctional Actuator
The actuator in this research is comprised of two main components, the
motor and the clutch/brake, and each component is associated with corresponding coils. The motor and clutch/brake are filled with MR fluids.
Multifunctional Actuators for Assistive Knee Braces
Generally, actuation devices in assistive knee braces can be classified as
active and semi-active actuators. The most widely used active actuators are
electric DC motors in rotary or linear forms. In addition to electric motors,
hydraulic and pneumatic actuators are other active actuators used in assistive knee braces and exoskeletons.
For active actuators, especially for electric DC motors, brake function requires
a large amount of power to maintain any posture and might cause safety problems. Some researchers have adopted smart fluids in actuation mechanisms;
for instance, a rehabilitative knee orthosis equipped with electrorheological
(ER) fluids-based actuators (Nikitczuk, Weinberg, and Mavroidis 2005). An
orthopedic active knee brace using a magnetorheological (MR) fluids-based
shear damper was developed to make the knee brace have controllable resistance (Ahmadkhanlou, Zite, and Washington 2007). All of the knee braces
developed using smart fluids provide controllable torque by passive and
semi-active means while consuming little power. Furthermore, according to
clinical gait analysis (CGA), the knee joint dissipates power during walking
(Zoss and Kazerooni 2006). Hence, the knee joint dynamics could be closely
matched by a controlled energy-dissipative device; for example, smart fluidsbased actuators. However, in some situations, such as going upstairs or stepping over obstacles, such knee braces do not help in active ways.
To combine the advantages of active and semi-active actuation devices,
like electric motors and smart fluids-based actuators, a hybrid assistive
knee brace that integrates an MR actuator with an electric motor was developed (J. Z. Chen and Liao 2010). The MR actuator can function as a brake
when adjustable torque is preferred and requires low power consumption
or it can work as a clutch to transfer torque from the motor to the brace.
With adaptive control, the actuation system worked well and could provide
the desired torque with better safety and energy efficiency. However, the
actuator seemed a bit bulky to be used on the human body and could not
fulfill the tasks of bidirectional rotation. Therefore, designing a more compact, multifunctional actuator is desired for assistive knee braces.
The objective of this research is to develop a novel actuator with multiple
functions such as motor, clutch, and brake for assistive knee braces. Utilizing
MR fluids, the actuator provides torque safely as a motor and clutch and produces controllable torque with little power consumption for braking. Moreover,
the braking torque control of the actuator could be easily implemented.
13.2 Design of Multifunctional Actuator
The actuator in this research is comprised of two main components, the
motor and the clutch/brake, and each component is associated with corresponding coils. The motor and clutch/brake are filled with MR fluids.