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Research Papers

Reducing Dynamic Loads From a Backpack During Load Carriage Using an Upper Body Assistive Device

[+] Author and Article Information
Joon-Hyuk Park

Robotics and Rehabilitation (ROAR) Laboratory,
Department of Mechanical Engineering,
Columbia University,
New York City, NY 10027
e-mail: jp3350@columbia.edu

Paul Stegall

Robotics and Rehabilitation (ROAR) Laboratory,
Department of Mechanical Engineering,
Columbia University,
New York City, NY 10027
e-mail: prs3146@columbia.edu

Sunil K. Agrawal

Professor
Fellow ASME
Robotics and Rehabilitation (ROAR) and
Robotic Systems Engineering
(ROSE) Laboratory,
Department of Mechanical Engineering,
Columbia University,
New York City, NY 10027
e-mail: Sunil.Agrawal@columbia.edu

1Corresponding author.

Manuscript received September 19, 2015; final manuscript received November 24, 2015; published online May 4, 2016. Assoc. Editor: James Schmiedeler.

J. Mechanisms Robotics 8(5), 051017 (May 04, 2016) (8 pages) Paper No: JMR-15-1272; doi: 10.1115/1.4032214 History: Received September 19, 2015; Revised November 24, 2015

This paper presents studies of an upper body assistive device designed to aid human load carriage. The two primary functions of the device are: (i) distributing the backpack load between the shoulders and the waist and (ii) reducing the dynamic load of a backpack on the human body during walking. These functions are targeted to relieve stress applied on the shoulders and the back, and also reduce the dynamic loads transferred to the lower limbs during walking. These functions are achieved by incorporating two modules—passive and active—within a custom fitted shirt integrated with motion/force sensors, actuators, and a real-time controller. The relevant modeling and controller design are presented for dynamic load compensation. Preliminary evaluation of the device was first performed on a single subject, followed by a pilot study with ten healthy subjects walking on a treadmill with a backpack. Results show that the device can effectively transfer the load from the shoulders to the waist and also reduce the dynamic loads induced by the backpack during walking. Reduction in peak and total normal ground reaction forces, leg muscle activations, and oxygen consumptions was observed with the device. This suggests that the device can potentially reduce the risk of musculoskeletal injuries and fatigue on the lower limbs associated with carrying heavy loads and provide some metabolic benefits.

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References

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Figures

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Fig. 1

Design of the upper body load assistive device (top) and the lifting mechanism (bottom)

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Fig. 2

Configuration of the active module (top) and design of the cable actuator (bottom)

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Fig. 3

Schematics of a 2DOF mass–spring–damper model to investigate the dynamics of the device in human load carriage

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Fig. 4

System response under (left) step and (right) sinusoidal disturbances for open-loop (solid line) and closed-loop (dashed line) control. First row to the fifth row, respectively, plots x,y−z,fr,fs,fc.

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Fig. 5

Controller gain tuning using (left) a manikin and (right) an instrumented test bed

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Fig. 6

Schematic of the state-feedback controller implemented in the real-time controller

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Fig. 7

System response after imposing the input condition (Eq. (12)), in which the assistive forces (fc) are provided only during the downward motion cycles of the base (z); open-loop control (solid line) and closed-loop control (dashed line)

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Fig. 8

Evaluation of the accelerometer sensor accuracy: (top) comparison on vertical displacements of the pelvis measured from Vicon motion capture system (solid line) with that computed from the on-board accelerometer (dashed line); (bottom) pelvis vertical excursion of five different walking speeds and RMSE of those computed using the accelerometer data

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Fig. 9

Experiment protocol used in the evaluation consisting of four sessions: S1 is the baseline walking session without a backpack and S2–S4 are the loaded walking sessions with varying configurations of the device

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Fig. 10

Experimental data from S3 where only the passive module was engaged to transfer 50% of backpack load from the shoulders to the waist: (top) pelvis vertical motion (mm) and (bottom) cable force equivalent to the spring force (fs) normalized to the backpack load

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Fig. 11

Force transmission from the shoulders to the waist in S3 (left) compared with S4 (right); fs(R) and fs(L), respectively, denote the spring force measured from the right and from the left side of the passive module; fc denotes the assistive force provided from the active module; fr denotes the sum of the spring forces in S3 and the sum of the spring and assistive forces in S4; and the assistive forces reduced the peaks of the total transferred force (fr) in S4 compare to S3

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Fig. 12

Comparison of the group average values of each metric between the loaded sessions. All values are normalized (unitless) and the error bars indicate ±STD. * indicates statistically significant difference between the pair (p < 0.05).

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