Research Papers

Second Spine: Upper Body Assistive Device for Human Load Carriage

[+] Author and Article Information
Joon-Hyuk Park

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

Xin Jin

Robotics and Rehabilitation (ROAR) Lab,
Department of Mechanical Engineering,
Columbia University,
New York, NY 10027
e-mail: xj2146@columbia.edu

Sunil K. Agrawal

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

Peak pelvic vertical acceleration is approximately ±2 m/s2 for normal walking [16].

1Corresponding author.

Manuscript received September 26, 2014; final manuscript received December 1, 2014; published online December 31, 2014. Assoc. Editor: Venkat Krovi.

J. Mechanisms Robotics 7(1), 011012 (Feb 01, 2015) (11 pages) Paper No: JMR-14-1269; doi: 10.1115/1.4029293 History: Received September 26, 2014; Revised December 01, 2014; Online December 31, 2014

This study presents the development of second spine, an upper body assistive device for human load carriage. The motivation comes from reducing musculoskeletal injuries caused by carrying a heavy load on the upper body. Our aim was to design a wearable upper body device that can prevent musculoskeletal injuries during human load carriage by providing a secondary load pathway—second spine—to transfer the loads from shoulders to pelvis while also allowing a good range of torso motion to the wearer. Static analysis of the backpack and the second spine was first performed to investigate the feasibility of our concept design. The development of second spine had two considerations: load distribution between shoulders and pelvis, and preserving the range of torso motion. The design was realized using load bearing columns between the shoulder support and hip belt, comprising multiple segments interconnected by cone-shaped joints. The performance of second spine was evaluated through experimental study, and its biomechanical effects on human loaded walking were also assessed. Based on the findings from second spine evaluation, we proposed the design of a motorized second spine which aims to compensate the inertia force of a backpack induced by human walking through active load modulation. This was achieved by real-time sensing of human motion and actuating the motors in a way that the backpack motion is kept nearly inertially fixed. Simulation study was carried out to determine the proper actuation of motors in response to the human walking kinematics. The performance of motorized second spine was evaluated through an instrumented test-bed using Instron machine. Results showed a good agreement with simulation. It was shown that the backpack motion can be made nearly stationary with respect to the ground which can further enhance the effectiveness of the device in assisting human load carriage.

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Fig. 1

Static modeling of backpack loading: unfilled arrows indicate the forces between the backpack and human interface, filled arrows indicate the resultant force acting on the body, and c.m denotes the center of mass of human torso; (a) general backpack loading induces vertical load and the moment about trunk, (b) backpack with a hip belt, and (c) backpack worn with load bearing device

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Fig. 2

Static analysis of backpack interface: unfilled arrows are the force components from a backpack while filled arrows indicate the reaction forces of the device in response to the backpack forces

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Fig. 3

Column modeling: (a) cone-shaped joint design, (b) two modalities of column configuration: stiff (on) and flexible (off), and (c) affixity condition of load bearing column

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Fig. 4

Mobility analysis in off configuration: (a) imposing parallel mechanism concept, (b) base platform A (hip belt) and moving platform B (shoulder support) geometry wherein OA and OB are the center of A and B, respectively, (c) desired workspace of B constructed from platform center (OB) range of motion, (d) conceptualizing 3D spherical motion about OA with radius d, (e) expressing vector qi in limb coordinate frame, and (f) cone-shaped segment characterization based on column bending angle β

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Fig. 5

Fabrication process of carbon fiber shoulder support

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Fig. 6

Second spine with adjustable design to fit between 25 and 75‰ male

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Fig. 7

Evaluation on second spine: (a) load versus lateral/axial deflection and shoulder load, (b) sum of transmitted force from shoulders to pelvis through second spine averaged over cycle for two loading conditions with three excitation frequencies at 0.8 in. (2 cm) amplitude, and (c) experimental apparatus

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Fig. 8

Trunk rotational range in sagittal, coronal, and transverse planes, represented as “tilt,” “obliquity,” and “rotation,” respectively, without backpack. Trunk angles are relative to the global frame.

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Fig. 9

Schematics of mass undergoing base excitation: (a) mass rigidly connected to the moving base and (b) active component modulating relative motion of the mass with respect to the base

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Fig. 10

Simulation results of force transmissibility of motorized second spine with amplitude ratio for different phase values

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Fig. 11

CAD drawings and physical models: (a) actuator units and (b) motorized second spine

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Fig. 12

Illustration of the system hardware configuration

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Fig. 13

Illustration of control algorithm with two control modalities: inertia compensation and posture adaptation

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Fig. 14

Evaluation on motorized second spine: (a) experiment setup, (b) vertical displacement of belt and shoulder support for three different conditions, and (c) left: force transmitted to the belt over time, and right: transmitted force averaged over cycle




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