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Design Innovation Paper

A Biologically Inspired Knee Actuator for a KAFO

[+] Author and Article Information
Feng Tian

Biomechanics and Assistive Technology Laboratory,
Department of Bioengineering,
The College of Engineering,
The University of Toledo,
2801 W. Bancroft Street, NI 5051,
Toledo, OH 43606;
Biomechanics and Assistive Technology Laboratory,
Department of Mechanical, Industrial,
and Manufacturing Engineering,
The College of Engineering,
The University of Toledo,
1610 N. Westwood,
Toledo, OH 43607;
Dynamic and Smart Systems Laboratory,
Department of Mechanical, Industrial,
and Manufacturing Engineering,
The College of Engineering,
The University of Toledo,
1610 N. Westwood,
Toledo, OH 43607
e-mail: ftian@rockets.utoledo.edu

Mohamed Samir Hefzy

Fellow ASME
Biomechanics and Assistive Technology Laboratory,
Department of Bioengineering,
The College of Engineering,
The University of Toledo,
2801 W. Bancroft Street, NI 5051,
Toledo, OH 43606;
Biomechanics and Assistive Technology Laboratory,
Department of Mechanical, Industrial,
and Manufacturing Engineering,
The College of Engineering,
The University of Toledo,
1610 N. Westwood,
Toledo, OH 43607
e-mail: Mohamed.Hefzy@utoledo.edu

Mohammad Elahinia

Fellow ASME
Dynamic and Smart Systems Laboratory,
Department of Mechanical, Industrial,
and Manufacturing Engineering,
The College of Engineering,
The University of Toledo,
1610 N. Westwood,
MS#312, Toledo, OH 43607
e-mail: Mohammad.Elahinia@utoledo.edu

1Corresponding author.

Manuscript received September 10, 2015; final manuscript received February 25, 2016; published online August 11, 2016. Assoc. Editor: Rita M. Patterson.

J. Med. Devices 10(4), 045001 (Aug 11, 2016) (8 pages) Paper No: MED-15-1258; doi: 10.1115/1.4033009 History: Received September 10, 2015; Revised February 25, 2016

Knee–ankle–foot orthoses (KAFOs) are prescribed to improve abnormal ambulation caused by quadriceps weakness. There are three major types of KAFOs: passive KAFOs, semidynamic KAFOs, and dynamic KAFOs. Dynamic KAFOs are the only type that enables to control knee motions throughout the entire walking gait cycle. However, those available in the market are heavy, bulky, and have limited functionality. The UT dynamic KAFO is developed to allow knee flexion and assist knee extension over the gait cycle by using a superelastic nitinol actuator, which has the potential to reduce volume and weight and reproduce normal knee behavior. In order to match the normal knee stiffness profile, the dynamic actuator consists of two actuating parts that work in the stance and swing phases, respectively. Each actuating part combines a superelastic torsional rod and a torsional spring in parallel. Geometries of the two superelastic rods were determined by matlab-based numerical simulations. The simulation response of the dynamic actuator was compared with the normal knee stiffness, verifying that the proposed design is able to mimic the normal knee performance. The surrounding parts of the dynamic knee joint have then been designed and modeled to house the two actuating parts. The dynamic knee joint was fabricated and mounted on a conventional passive KAFO, replacing its original knee joint on the lateral side. Motion analysis tests were conducted on a healthy subject to evaluate the feasibility of the UT dynamic KAFO. The results indicate that the UT dynamic KAFO allows knee flexion during the swing phase of gait and provides knee motion close to normal.

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References

Figures

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Fig. 1

Kinematics and kinetics characteristics for three individuals with different levels of quadriceps weakness: (a) and (b) are for slight weakness, (c) and (d) are for medium weakness, and (e) and (f) are for severe weakness. The figure is adopted from Ref. [3].

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Fig. 2

Phase diagram for nitinol alloys with SE. The figure is adopted and modified from Ref. [8].

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Fig. 3

Flexion angle change of a normal knee joint during the entire walking gait cycle. The figure is adopted from Ref. [12].

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Fig. 4

Body weight-normalized internal moment of a normal knee joint during the entire walking gait cycle. The figure is adopted from Ref. [12].

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Fig. 5

The stiffness profile for a normal knee joint: normalized internal knee moment versus knee flexion angle. The figure is adopted from Ref. [22].

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Fig. 6

Conceptual design of the dynamic knee actuator

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Fig. 7

Isothermal and adiabatic simulation results for the superelastic nitinol rod used in the stance actuating part: torque versus angle of rotation

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Fig. 8

Isothermal and adiabatic simulation results for the superelastic nitinol rod used in the swing actuating part: torque versus angle of rotation

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Fig. 9

Stiffness profile of the dynamic knee actuator and that of a normal knee joint. The figure is adopted from Ref. [15].

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Fig. 10

Isothermal and adiabatic simulation results for the superelastic nitinol rod used in the stance actuating part: shear stress versus shear strain

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Fig. 11

Isothermal and adiabatic simulation results for the superelastic nitinol rod used in the swing actuating part: shear stress versus shear strain

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Fig. 12

The conceptual design of the dynamic knee joint: (1) the internal frame of the knee joint; (2) the external frame of the knee joint; (3) the stance actuating part; (4) the swing actuating part; and (5) two push–pull solenoids. This figure is adopted from Ref. [12].

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Fig. 13

The prototype of the UT dynamic KAFO

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Fig. 14

The location of the markers and the EMG sensors when testing with the UT dynamic KAFO

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Fig. 15

Comparison of the knee angle patterns between normal walking, walking with the locked KAFO, and walking with the dynamic KAFO

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Fig. 16

Comparison of the normalized knee moment profiles between normal walking, walking with the locked KAFO, and walking with the dynamic KAFO

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