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Research Papers

Biologically Inspired Design and Development of a Variable Stiffness Powered Ankle-Foot Prosthesis

[+] Author and Article Information
Alexander Agboola-Dobson

School of Mechanical,
Aerospace and Civil Engineering,
The University of Manchester,
Manchester M13 9PL, UK
e-mail: alex-dobson@outlook.com

Guowu Wei

Mem. ASME
School of Computing,
Science and Engineering,
University of Salford,
Salford M5 4WT, UK
e-mail: g.wei@salford.ac.uk

Lei Ren

School of Mechanical,
Aerospace and Civil Engineering,
The University of Manchester,
Manchester M13 9PL, UK
e-mail: lei.ren@manchester.ac.uk

1Corresponding authors.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the Journal of Mechanisms and Robotics. Manuscript received July 2, 2018; final manuscript received April 13, 2019; published online May 17, 2019. Assoc. Editor: Pinhas Ben-Tzvi.

J. Mechanisms Robotics 11(4), 041012 (May 17, 2019) (15 pages) Paper No: JMR-18-1195; doi: 10.1115/1.4043603 History: Received July 02, 2018; Accepted April 16, 2019

Recent advancements in powered lower limb prostheses have appeased several difficulties faced by lower limb amputees by using a series-elastic actuator (SEA) to provide powered sagittal plane flexion. Unfortunately, these devices are currently unable to provide both powered sagittal plane flexion and two degrees of freedom (2-DOF) at the ankle, removing the ankle’s capacity to invert/evert, thus severely limiting terrain adaption capabilities and user comfort. The developed 2-DOF ankle system in this paper allows both powered flexion in the sagittal plane and passive rotation in the frontal plane; an SEA emulates the biomechanics of the gastrocnemius and Achilles tendon for flexion while a novel universal-joint system provides the 2-DOF. Several studies were undertaken to thoroughly characterize the capabilities of the device. Under both level- and sloped-ground conditions, ankle torque and kinematic data were obtained by using force-plates and a motion capture system. The device was found to be fully capable of providing powered sagittal plane motion and torque very close to that of a biological ankle while simultaneously being able to adapt to sloped terrain by undergoing frontal plane motion, thus providing 2-DOF at the ankle. These findings demonstrate that the device presented in this paper poses radical improvements to powered prosthetic ankle-foot device (PAFD) design.

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References

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Figures

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Fig. 1

(a) CAD render of the final PAFD design, (b) sagittal plane cut-out diagram, and (c) CAD render of the PAFD being worn by a user

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Fig. 2

Kinematic diagram of the PAFDs: (a) sagittal plane and (b) frontal plane

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Fig. 3

The intended motion of the PAFD in the sagittal (a) and frontal (b) planes. The key gait events, periods, and subphases represented are (1) HS, (2) CD, (3) HO, (4) PP, (5) TO, and (6) SW.

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Fig. 4

Desired displacement of the actuator and SEA. The SEA displacement data were generated using desired ankle angle data from Ref. [1]; graph plotted in the style of Ref. [25].

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Fig. 5

CAD render and photographs of the PAFD (including control system)

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Fig. 6

Close up of the U-joint ankle mechanism: (a) forward PDMA, (b) U-joint top, (c) heel PDMA, (d) U-joint base, (e) IEMA, and (f) FPS

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Fig. 7

The assembled prosthetic foot: (a) ankle platform, (b) right stabilizer, and (c) left stabilizer

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Fig. 8

Classification trees for the determination of (a) prosthetic toe, (b) heel states, and (c) gait events by utilizing the toe and heel states; TRUE means there is contact with the ground, whereas FALSE means there is no contact; and (d) the current gait subphase

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Fig. 9

Heel and toe pressure sensors

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Fig. 10

The actuator sensor setup, showing the IR range sensor and the reflective panel. The actuator length, Latc, is taken as the distance between the IR sensor and the reflective panel.

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Fig. 11

Setup used to emulate the motion of the lower limb during a walking gait cycle: (a) PAFD lowered to the ground for HS, (b) CP and CD takes place as the operator applies their weight onto the PAFD, (c) PP causes the PAFD to lift the weight of the operator, and (d) the PAFD is lifted from the ground for HO. This setup allowed for a large amount of force to be consistently applied across all trials.

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Fig. 12

Experimental setup of the PAFD. The positions of the IR markers were (a) right toe 1, (b) left toe 1, (c) right toe 2, (d) left toe 2, (e) ankle right, (f) ankle left, (g) ankle forward, (h) ankle back, (i) shank right, and (j) shank left.

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Fig. 13

The force-plate setup for (a) session 1, (b) session 2, and (c) the general setup for all experiments

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Fig. 14

Graphical representation of the vectors used to calculate ankle angle and ankle torque. Points A to J represent the captured marker positions, and points K and L represent calculated positions.

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Fig. 15

Ankle angle in the sagittal plane for a single trial from studies (a) 1A-I and 1A-II, and (b) 1B-I and 1B-II. The time period for the shown trails is (a) 7.07 s and 7.61 s for “FSS” and “no FSS,” respectively, and (b) 5.1 s and 4.45 s for “FSS” and “no FSS,” respectively. For comparison, the desired ankle angle using data modified from Ref. [24] is also displayed.

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Fig. 16

Ankle angle in the sagittal plane for a single trial from studies (a) 2A-I and 2A-II, and (b) 2B-I and 2B-II. The time period for the shown trails is (a) 6.65 s and 6.52 s for “FSS” and “no FSS,” respectively, and (b) 4.39 s and 3.51 s for “FSS” and “no FSS,” respectively. For comparison, the desired ankle angle using data modified from Ref. [24] is also displayed.

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Fig. 17

Ankle angle in the frontal plane for a single trial from studies (a) 2A-I and 2A-II, and (b) 2B-I and 2B-II. The time period for the shown trails is (a) 6.65 s and 6.52 s for “FSS” and “no FSS,” respectively, and (b) 4.39 s and 3.51 s for “FSS” and “no FSS,” respectively.

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Fig. 18

Ankle torque in the sagittal plane for a single trial from studies (a) 1A-I and 1A-II, and (b) 1B-I and 1B-II. The time period for the shown trails is (a) 7.07 s and 7.61 s for “FSS” and “no FSS,” respectively, and (b) 5.1 s and 4.45 s for “FSS” and “no FSS,” respectively. For comparison, biological ankle torque data from Ref. [23] are also displayed.

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Fig. 19

Ankle torque in the sagittal plane for a single trial from studies (a) 2A-I and 2A-II, and (b) 2B-I and 2B-II. The time period for the shown trails is (a) 6.65 s and 6.52 s for “FSS” and “no FSS,” respectively, and (b) 4.39 s and 3.51 s for “FSS” and “no FSS,” respectively. For comparison, biological ankle torque data from Ref. [23] are also displayed.

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Fig. 20

Ankle torque against ankle angle in the sagittal plane for a single trial from studies (a) 1A-I and 1A-II, and (b) 1B-I and 1B-II. By calculating the area enclosed within each plot, the net work is calculated. Powered net work: 0.1976 J kg−1 (FSS) and 0.302 J kg−1(no FSS). Passive net work: −0.0961 J kg−1 (FSS) and −0.0426 J kg−1 (no FSS). The time period for the shown trails is (a) 7.07 s and 7.61 s for “FSS” and “no FSS,” respectively, and (b) 5.1 s and 4.45 s for “FSS” and “no FSS,” respectively.

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Fig. 21

Ankle torque against ankle angle in the sagittal plane for a single trial from studies (a) 2A-I and 2A-II, and (b) 2B-I and 2B-II. By calculating the area enclosed within each plot, the net work is calculated. Powered net work: 0.2150 J kg−1 (FSS) and 0.2285 J kg−1(no FSS). Passive net work: −0.0491 J kg−1 (FSS) and −0.0395 J kg−1 (no FSS). The time period for the shown trails is (a) 6.65 s and 6.52 s for “FSS” and “no FSS,” respectively, and (b) 4.39 s and 3.51 s for “FSS” and “no FSS,” respectively.

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