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TECHNICAL PAPERS: Joint/Whole Body

Design and Demonstration of a New Instrumented Spatial Linkage for Use in a Dynamic Environment: Application to Measurement of Ankle Rotations During Snowboarding

[+] Author and Article Information
Josh Nordquist

Department of Mechanical Engineering, University of California at Davis, One Shields Avenue, Davis, CA 95616

M. L. Hull1

Department of Mechanical Engineering, and Biomedical Engineering Program, University of California at Davis, One Shields Avenue, Davis, CA 95616mlhull@ucdavis.edu1

1

Corresponding author.

J Biomech Eng 129(2), 231-239 (Jun 30, 2006) (9 pages) doi:10.1115/1.2486107 History: Received July 14, 2005; Revised June 30, 2006

Joint injuries during sporting activities might be reduced by understanding the extent of the dynamic motion of joints prone to injury during maneuvers performed in the field. Because instrumented spatial linkages (ISLs) have been widely used to measure joint motion, it would be useful to extend the functionality of an ISL to measure joint motion in a dynamic environment. The objectives of the work reported by this paper were to (i) design and construct an ISL that will measure dynamic joint motion in a field environment, (ii) calibrate the ISL and quantify its static measurement error, (iii) quantify dynamic measurement error due to external acceleration, and (iv) measure ankle joint complex rotation during snowboarding maneuvers performed on a snow slope. An “elbow-type” ISL was designed to measure ankle joint complex rotation throughout its range (±30deg for flexion/extension, ±15deg for internal/external rotation, and ±15deg for inversion/eversion). The ISL was calibrated with a custom six degree-of-freedom calibration device generally useful for calibrating ISLs, and static measurement errors of the ISL also were evaluated. Root-mean-squared errors (RMSEs) were 0.59deg for orientation (1.7% full scale) and 1.00mm for position (1.7% full scale). A custom dynamic fixture allowed external accelerations (5g, 050Hz) to be applied to the ISL in each of three linear directions. Maximum measurement deviations due to external acceleration were 0.05deg in orientation and 0.10mm in position, which were negligible in comparison to the static errors. The full functionality of the ISL for measuring joint motion in a field environment was demonstrated by measuring rotations of the ankle joint complex during snowboarding maneuvers performed on a snow slope.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 8

Slalom course used in measuring snowboard boot rotations in the field. The individual turns were set 8m from the fall line and 8m downhill from the previous turn. The slalom course had a total of 12 turns, 5 are shown here (T1-T5). For a regular stance, T1, T3, T5, etc., are heel-side turns (left foot forward). For a goofy stance, T1, T3, T5, etc., are toe-side turns (right foot forward).

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Figure 9

(a,b) Snowboard boot rotations of the trailing foot (a) and the leading foot (b) for a subject traveling through the slalom course (Fig. 8). The left foot is the leading foot for a regular stance, while the right foot is the leading foot for a goofy stance. These example data were collected from individual runs.

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Figure 1

Designed elbow-type ISL, which complies with all the designated design criteria: a grouping of two revolute joints at one end (axes 1 and 2) and a grouping of three revolute joints at the other end (axes 4–6). The two groupings are connected via two links attached and the sixth revolute joint (axis 3). The fourth, fifth, and sixth revolute joint axes intersect.

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Figure 2

Cutaway of a revolute joint assembly illustrating the joint compression design, external potentiometer mounting, potentiometer protective casing, wire routing, and wire strain relief

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Figure 3

Coordinate systems that were established at both the fixed and moving ends of the ISL. Orientation of these coordinate systems was chosen to be parallel at the neutral configuration. The ISL is in the defined neutral configuration.

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Figure 4

Calibration device that offers three degrees of freedom with three revolute axes that intersect at the center of rotation (COR). The calibration device is in the defined neutral position.

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Figure 5

Fixture designed to provide rigid installment of the ISL and mounting points for applying external acceleration in three acceleration directions

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Figure 6

(a,b) Modifications to the snowboard boot to accept rigid mounting of the ISL. Soft material in the sole was replaced with fiberglass-reinforced epoxy to accept the ISL sole mount (a, circled). A fiberglass-reinforced epoxy plate was molded to fit inside the boot cuff to allow a rigid mount for the ISL cuff mount (b, circled).

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Figure 7

The ISL mounted to the right snowboard boot of the subject performing a heel-side turn with a regular stance. Also visible are the ISL sole mount and cuff mount, along with the ISL data cable which travels up the right leg and into a backpack.

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